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SP-4212
- On
Mars: Exploration of the Red Planet. 1958-1978
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- 11
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- ON MARS
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- [363] As
anticipated, the information relayed to Earth by the Viking
spacecraft has greatly affected man's perceptions and
understanding of the planet Mars. The increase in basic, directly
confirmed knowledge of the Red Planet began even before the
landings. Once in orbit, the spacecraft began transmitting the
first of tens of thousands of images of the planet and its
satellites.
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IMAGES FROM ORBIT
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of Mars as scientists identified a greater variety of terrains
than known to exist on the moon or Mercury. Conway B. Leovy, a
member of the meteorology team, noted: "Unlike the moon, whose
story appears essentially to have ended one or two billion years
ago, Mars is still evolving and changing. On Mars, as on the
earth, the most pervasive agent of change is the planet's
atmosphere, itself the product of the sorting of the planet's
initial constituents that began soon after it condensed from the
primordial cloud of dust and gas that gave rise to the solar
system 4.6 billion years ago." 1
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- Some information about the nature of the
Martian atmosphere had been derived from telescopic observations
and from earlier Mariner missions, but those sources of data were
"unverifiable and subject to misinterpretation." With the
exception of its significantly different composition and its being
"less than a hundredth as dense as that of the earth," the
atmosphere of Mars behaves much like that of our own planet. "It
transports water, generates clouds and exhibits daily and seasonal
wind patterns." Responding to seasonal changes in the heat
generated by solar radiation, localized dust storms occur and
sometimes grow in strength until they cover the entire planet, a
fact with which Mariner and Viking specialists were familiar.
Global dust storms appear to be a phenomenon unique to Mars, which
lacks large bodies of water that would prevent their
buildup.
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- Atmospheric weathering of the primitive
crystalline rocks on Mars has reduced them to fine particles that
have oxidized and combined chemically with water to produce the
reddish minerals so apparent in the color images
[364] returned
from the Viking landers. Whereas on Earth the dominant weathering
process has been from the movement of liquid water, on Mars the
primary agent of change has been the wind. It erodes the
landscape, transports the dust, and deposits it elsewhere on the
planet. The Viking landing sites appear to have been "severely
scoured by winds. In addition, pictures taken by the orbiter
cameras reveal deep layers of wind-borne sediment in the polar
regions, while dunefields of Martian dust and sand much larger
than those on Earth were observed near the north pole.
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- The geologic history of Mars, according to
orbiter imaging team leader Michael H. Carr, "shows evidence of
floods and relatively recent volcanic eruptions, at least in the
hundreds of millions of years that geology uses as a measure."
There are also features that resemble terrestrial river systems.
"Apparently tremendous floods occurred many times over Mars'
history, indicating that the planet must have been drastically
different in the past." 3
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- Earlier Mariner flights indicated the
presence of volcanoes on Mars; Viking measured their extent and
variety. A large portion of the northern hemisphere is covered by
volcanoes, sonic spreading broad lava fields for hundreds of
kilometers. Others, such as Olympus Mons and Arsia Mons, rise some
27km above the reference surface level of the planet. Distinct
lava flow patterns can be seen 300km from their source in Arsia
Mons, with the general pattern of the terrain indicating that the
lava may have traveled up to 800 km, the distance from Washington,
D.C. to Cincinnati, Ohio. 4 Geologists who have studied the Viking photographs
believe that the nature of volcanic activity on Mars is
essentially the same as that on Earth-the movement of a basaltic,
low-viscosity lava. One kind of volcano appears to be unique to
Mars: the patera, or saucer-shaped, volcano with a low profile
covering a vast area. Alba Patera, with a maximum diameter of 1600
km, is probably the largest such volcano on the planet. A similar
volcano centered on Denver would have spilled its lava across all
of Colorado, Wyoming, Utah, large parts of New Mexico, Kansas,
Nebraska, South Dakota, and corners of Montana, Idaho, Arizona,
Texas, and Oklahoma. Scientists think that the caldera-the crater
formed by the collapse of the central part of the volcano-of a
patera is the result of simultaneous lifting and collapsing of the
sides of the volcano, probably repeated many times over a long
period. According to Carr, "the total volumes of lava erupted to
produce single flows are orders of magnitudes greater than they
are in terrestrial lava flows, and the total volumes of lava
erupted from essentially a single vent volcano are enormous."
5 Production of sufficient magma (molten rock) for
such lava flows cannot be explained, but as Carr pointed out, the
plains regions appear to have been formed several million years
ago by this movement of lava. 6
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- In addition to lava, the movement of water
also has affected Martian topography. The large riverlike channels
are one of the big Martian puzzles. Carr and his colleagues
believe there are two major kinds of water features:
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- [365] There are
the large flood features and then there are dendritic or branching
drainage features that resemble terrestrial river systems. It
appears from the crater counts that the fine terrestrial-like
river channel systems are older than the flood features. It
appears that the large flood features came in middle Mars history.
There was a period of vast floods, then the flooding for some
reason ceased or became less frequent because we don't have flood
features with crater cutouts comparable to those we find on the
Tharsis volcanoes. Very early in Mars' history, dendritic drainage
patterns developed; in Mars' middle history it had a period of
flooding, and then mostly after that the volcanics of Tharsis
accumulated. This general picture has collie out of the Viking
data.
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- A lot of skeptics didn't believe there had
been any period of surface drainage. Some said all those things
could easily have been formed by faulting and soon. The Viking
pictures are full of examples of dendritic channels. I can't
believe there are many skeptics left. I think we have really
established that there was this early period of surface drainage.
There can be very little doubt about that. 7
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- The scientists are still left with
explaining where all the water for the floods and rivers came
from. More important, where did it go?
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- Because of low atmospheric pressure at the
surface, there are no con- temporary large pools, rivers, or
collection basins filled with water, and because of low
temperatures the atmosphere cannot contain much water. However,
there is probably a great quantity in the permanent polar caps and
within the surface. The low pressure permits water to be present
only in the solid (ice) or gaseous (water vapor) state. One
possible explanation for the apparently contradictory vision of
rushing rivers on Mars was presented by Gerald A. Soffen: "Broad
channels formed when subsurface water-ice (permafrost) was melted
by geothermal activity from deep volcanic centers. When the
melting of the permafrost reached a slope the interstitial water
suddenly released great flows, sometimes a hundred kilometers wide
that modified the channels." 8 Seasonal heating of the permafrost may have
occasionally released large flows of water, as well-a possible
explanation for the channels that originate in box canyons and
spill onto the plains. The easiest method of accounting for the
dendritic channels is to conjure up a Martian rainstorm, but that
suggestion raises many problems, all of which hinge on the basic
question: "How is it possible that these ancient rivers could
[have] existed and there be none today?" Obviously, atmospheric
pressure would have to have been different during such a period.
This hypothesis seems to be supported by studies of the Martian
atmosphere encountered by Viking.
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- If the atmospheric pressure once was
sufficient to permit the formation of liquid water, how long ago
was that? This is still a subject of some debate. Harold Masursky
and his colleagues estimated the relative age of the channels by
counting the number and judging the age of the craters in and near
the channels. The different kinds of channels appear to have been
created in....
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- [366]
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- The Martian volcano
Olympus Mons, at top, was photographed by the Viking I
orbiter 31 July 1976 from a distance of 8000 km. The
27-km-high mountain is wreathed in clouds extending 19
km up its flanks. The clouds are thought to be
principally water ice condensed as the atmosphere
cools. The crater is some 80 km across. At left, Arsia
Mons, called South Spot during Mariner 9 mission, is
shown in a mosaic of photos taken 22 August. The
crater is 120 km across, and the peak rises 16 km
above the Tharsis Ridge, itself 11 km high. Vast
amount of lava have flooded the plains.
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[367]
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- A July 9 mosaic of Viking
1 orbiter photos above shows lava flows broken by faults
forming ridges. Apparently a small stream once flowed
northward (toward upper right) from Lunae Planum, crossed
the area, and descended toward the east. In places water
may have formed ponds behind ridges before cutting
through. At right, a fresh young crater about 30 km
across, in Lunae Planum, is near a dry river channel
running alongside a cliff in possible lava flows (Kasei
Valley). Below, an oblique view across Argyre Planitia
(the relatively smooth plain at top center of the photo)
shows surrounding heavily cratered terrain. Brightness of
the horizon to the right (with north toward upper left)
is due mainly to a thin haze. Above the horizon are
detached layers of haze 25 to 40 km high, thought to be
crystals of carbon dioxide (dry ice). Both the lower
photo mosaics were taken 11 July.
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- [368]....different
epochs, or episodes, and all of them at least 50 million years ago
and perhaps as long ago as several billion years.
9
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- In addition to the effects of lava and
water, shifting of the permafrost also is believed to have
influenced the texture of the planet's surface. Investigators
assume the existence of permafrost, sometimes to the depth of
several kilometers and generally thought to have been present for
billions of years. Carr stated:
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- To me one of the more exciting things
we've observed is the abundant evidence of permafrost. The most
striking features indicative of permafrost occur along the edge of
old crater terrain. They form by mass movement of surface material
probably aided by the freezing and thawing of ground ice. Another
possible indicator of ground ice is the unique character of
material ejected from impact craters that is quite different from
the pattern on the Moon and on Mercury. We interpret the
difference as due to ground ice on Mars. The impact melts the
ground ice and lubricates the [ejecta] that is thrown out of the
crater so when it lands on the ground it flows away from the
crater in a debris flow and forms the characteristic features we
have observed.
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- Slow movement and a freeze-thaw cycle
could account for the chaotic, jumbled terrain seen over vast
stretches of the Martian surface. Irregular depressions caused by
localized collapsing of the crust when permafrost thawed could
have formed the flat-floored valleys in Siberia and the
table-lands of Mars. Large polygonal patterned regions on Mars
resemble the ice wedges in terrestrial glacial areas.
10
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- The Martian class of lobate craters is
distinct. Unlike lunar craters and those photographed on Mercury,
which have radial sunburst patterns caused by ejected debris, on
Mars debris apparently flowed smoothly away from the points of
impact of many craters. Craters on the moon and Mercury typically
had a coarse, disordered texture close to the rim that became
finer farther out, grading almost imperceptibly into dense fields
of secondary craters. "The most distinctive Martian craters have a
quite different pattern. The ejecta commonly appears to consist of
several layers, the outer edge of each being marked by a low ridge
or escarpment." Recognized in Mariner 9
photographs, the shape was attributed to erosion caused by the
wind. With improved-resolution Viking photographs, the geologists
have changed their minds; they theorize that on Mars objects also
struck the surface with explosive force, but the difference lay in
the heating of the permafrost. Resulting steam and momentarily
liquid water transported surface materials away from the point of
impact and created the distinct lobate flow patterns around the
central point. Where the crater ejecta patterns do resemble those
on the moon and Mercury, geologists believe that the permafrost
was too far below the surface to have been heated, or else
possibly absent. 11
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- On a planet that has many spectacular
features, one of the most interesting is the Valles Marineris, the
Grand Canyon of Mars. First [369] observed by
Mariner 9 cameras, only the gross proportion of the canyon
system were appreciated at the 1- to 1.5-km resolution. A small
sample of higher resolution Mariner
9 photographs (100- 150 meters)
hinted at the huge landslides and related features that would be
seen on the canyon walls and floors. The images from Viking were
much better (resolution of objects as small as 40 meters), and
many parts of the 4000-km-long canyon were photographed in stereo,
the combination permitting geologists to understand more precisely
the processes that formed it. Significantly, neither volcanic
activity nor erosion caused by flowing water seems to account for
the changes in the Valles Marineris. After examining the Viking
photos, Karl R. Blasius and his colleagues believe that tectonic
shifting of the planet's crust may have enlarged the canyons.
Volcanism was not seen in the Viking images, they point out, and
evidence of fluvial activity was only indirect, from chaotic
terrain. But tectonic activity appeared to have been prolonged,
deepening canyons and offsetting erosion and deposits that would
have broadened and filled them. Vertical adjustment of crustal
blocks under north-south and east-west extensional stresses
appeared to have been the primary process. Some blocks may also
have tilted, forming "peculiar slopes near canyon rims and on the
intratrough plateau and possibly causing the formation of strings
of collapse pits." The history of canyon erosion and deposits was
also more complex than had been realized. "Layered materials,
including some very regularly imbedded sediments first recognized
in the Viking images,'' were highly diverse and widespread.
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- One of the basic reasons for studying the
Valles Marineris was an interest in the interrelations through
time of the volcanic and tectonic forces that produced the large
volcanoes to the west-Olympus Mons and the Tharsis craters, which
include Arsia Mons-and the development and....
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- Material appears to have flowed
out of the Arandas crater on Mars, rather than being blasted out
by the meteorite impact. Radial grooves on the surface of the flow
may have been eroded during the last stages of the impact process.
Photographed 22 July 1976 by the Viking 1 orbiter at 43°N
latitude, 15° longitude, Arandas is about 25 km in
diameter.
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[370]
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More than 100 photos form the
top mosaic mapping Valles Marineris, huge Martian complex of
Canyons. Taken by the Viking 1 orbiter 23-26 August 1976,
they are centered at 5° south latitude, 85°
longitude, with north at the top. Ten photos taken 22 August
form the center mosaic of the western end of the canyon. The
volcanic plateau is deeply dissected into connected
depressions.
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[371]....evolution of
the canyon lands. Both geological regions are young in terms of
the life of the planet, and changes in both areas likely have
continued to the present. Mars and Earth may thus be more alike in
geological terms than previously expected. The Viking images have
contributed to a new field of study called comparative
planetology. Undoubtedly, the wealth of new information gathered
by the cameras on the orbiter was ample reward to the people who
had fought so strongly to send an improved imaging system to Mars
to complement the scientific instruments. As Mike Carr and his
associates had predicted in October 1970, "The high-resolution
imaging system may be considered as the "meat and potatoes"
low-risk but guaranteed-significant-gain experiment in the
mission." 13
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- Further analysis of the photographs taken
over the Chryse and Cydonia regions during and after landing site
certification had indicated that many of the assumptions
specialists had made on the basis of Mariner 9
photography had to be changed. Viking science investigators
benefited from approaching the planet at a time when it was far
from the sun, since lower solar radiation nearly eliminated the
worry about dust storms. 14 The clarity of the Viking orbiter images indicated
that the Martian atmosphere probably had never cleared during the
Mariner 9 mission. Viking 1
arrived at Mars just before the
beginning of summer in the northern hemisphere and soon after
aphelion. Every Viking scientist reaped benefits from the clear
orbiter images, and Ronald Greeley and his geologist colleagues
had specific comments about the importance of the Viking orbital
pictures in the Chryse and Cydonia regions: "High-resolution
Viking orbiter images show Chryse Planitia to be much more complex
than had been suspected from Mariner
9 images. Ancient heavily cratered
terrain appears to form the basement for the basin. Much of its
heavily cratered terrain is mantled with deposits that may be of
aeolian, fluvial, or volcanic origin." 15 They were certain that the Mariner 9 view of Mars
had been "simplistic." From a close examination of the southern
hemisphere, scientists had made some false assumptions about the
northern half of the planet. "From Viking photography it is
suggested that not only is the northern hemisphere more
complicated than was expected, but as....predicted, although the
present surfaces are young, some of the rocks exposed at the
surface may be old." 16
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- Orbiter photographs coupled with data from
the infrared thermal mapper (IRTM) gave scientists a new
understanding of the polar caps, too. The Martian poles change
dramatically with the seasons. When the Viking craft arrived at
the planet, the northern cap had shrunk to its minimum size,
revealing the permanent cap, which-contrary to some expectations-
consisted of water ice. The part that had dissipated had been made
of solid carbon dioxide, dry ice. Meanwhile, the southern ice cap
expanded. The northern polar region displayed terraced deposits,
indicating an episodic pattern of rapid erosion and deposition of
materials. "An unconformity within the layered deposits suggests a
complex history of climate change during their time of
deposition."
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- [372]Table
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Geological Evolution of
Martian North Polar Region
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Stage 1
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Onset of polar activity.
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- Moderate aeolian modification
of ancient volcanic terrains.
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Stage 2
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First depositional period.
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- Layered deposits of silicate
dust and possibly interbedded ice accumulate to
thickness of several kilometers.
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Stage 3
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First erosional period.
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- Erosional attack of layered
deposits results in landscape of gently curving scarps
and channels with terraced slopes.
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Stage 4
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Second depositional period.
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- More layered deposits
accumulate unconformably on top of units formed first
depositional period.
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Stage 5
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Second erosional period.
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- Further erosional attack of
layered deposits results in exhumation of earlier
formed landscapes and reveals unconformable contacts
between deposits of first and second depositional
period. Some eroded material reaccumulates as girdle
of sand dunes between 75°N and 80 N.
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Stage 6
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Recent period.
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- Ice in permanent polar cap
assumes its present form and distribution.
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completely accurate explanation of the manner in which the polar
terrain evolved, James A. Cutts, Karl Blasius, and associates
argue that "it does offer a credible framework....against which
further observations and theoretical models may be tested."
17
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- Meanwhile at the south pole, the infrared
thermal-mapping team had observed some interesting temperatures.
In their first report in Science
, Hugh H. Kieffer and his
colleagues noted that "areas in the polar night have temperatures
distinctly lower than the CO2 condensation
point at the surface pressure. "From the atmospheric pressure of 6
millibars at the south pole, the mapping team had anticipated
temperatures of about 125°C, the equilibrium temperature for
carbon dioxide at that pressure, but, when initial results came
in, temperatures as low as 139°C were recorded. The infrared
specialists decided that this extra cooling was attributable to a
freezing out of the carbon dioxide, leaving a higher concentration
of non-condensable gases (such as nitrogen and argon) than is
normal for the atmosphere elsewhere. Since these gases would not
condense into solid form at - 139°C, that could explain the
cooling, but other questions were raised by this theory.
18 How did the non-condensable gases concentrate in
the polar region? What did this phenomenon mean for global
circulation patterns? What did it tell scientists about the
movement of carbon dioxide and other gases from one pole to the
other during the change of seasons?
[373] Once again,
new knowledge raised as many questions as it answered.
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infrared thermal-mapping team had begun to devise theories to
answer some of the questions. Large-scale patterns in the
temperatures of Mars appear to be similar in size to continental
weather patterns on Earth. Viking scientists believe that these
patterns may be associated with cloud patterns. As team leader
Hugh Kieffer put it, "It's possible we're seeing what I call
continental scale weather." Temperatures shortly before dawn in
some places are much cooler than expected. Over the Valles
Marineris, the temperatures were unexpectedly quite warm before
dawn. Kieffer noted that "the temperatures just before dawn are
more directly related to the physical properties of the surface
because there is no solar energy being absorbed during the 12
hours of night. This means the temperatures are a good indication
of how well the surface can hold its heat." 19
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- Infrared thermal-mapping measurements
indicated wide daily temperature variations on Mars. The typical
day-night variation on Earth is 5° to 10°C, but on Mars
the temperature can go from a low of -133° to a high of
4°C. The reason for this wide range is not yet fully
understood, nor is the tendency of the temperatures in the
afternoon to drop much more quickly than expected. Keiffer
reported that in several regions on Mars temperatures begin toward
the middle of the afternoon to drop more rapidly than predicted
until just before dusk. They may be 10 to 15 degrees cooler than
expected. Then they "cease to drop so rapidly and slowly merge
with the predictions for the evening." In the afternoon, "the only
atmospheric regions that are cooler than the surface are very high
and thus we don't know what process at the moment is causing this
rapid surface cooling." The process "may be related to clouds in
some way, but most of the atmosphere near the ground, where one
expects clouds to form, is, in fact, warmer than the surface just
before sunset." 20
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- A more important contribution from the
infrared thermal-mapping experiment was the discovery of the
nature of the polar ice cap. One of the major questions posed by
the Mariner 9 data was the composition of the residual polar cap
left when the winter polar cap, made of frozen carbon dioxide,
retreated in midsummer. A major controversy existed over whether
this summer cap seas also frozen carbon dioxide or was frozen
water. According to Viking data, the temperatures of the residual
cap are near -68° to -63°C, making a case for water
frost. Also. the brightness of the frost "indicates it has a lot
of dirt mixed in with it. The dirty nature of the ice had also
been seen now by the orbital imaging system." Apparently there is
no permanent reservoir of carbon dioxide in the polar regions of
Mars, a finding that tends to rule out the theory of a rapid
climate change induced by the instability of the carbon dioxide on
the planet. "This means we still don't have an adequate
explanation of how the atmosphere could have been of sufficient
density to sustain the liquid water that appears to have flowed at
one time in streams and rivers on the surface of Mars,'' said
Kieffer. 21
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- MEASURING THE
ATMOSPHERE
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- [374] The
water-vapor-mapping investigation was designed to map the
distribution of water vapor over the planet and to determine the
pressure of the atmosphere at the level where vapor is present.
Understanding the distribution of water vapor is crucial to
understanding the geological features of Mars and the possibility
of the existence of life. Viking's measurements of water vapor
varied, depending on the location, season, and time of day.
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- Specialists discovered a direct
correlation between elevation and the amount of water vapor
present, with the lowest points on the planet having the greatest
concentrations and the highest features the minimum. More water
vapor was found during the summer season than during winter, when
it was barely perceptible. In regions of rough terrain, there were
marked daily variations in water vapor, and C. Barney Farmer and
his team believed the variations were attributable to local
phenomena-shifting wind patterns, dust, or a thin cloud or haze
that is present at dawn but dissipates by noon. For example, early
in the first mission one site was monitored over a six-hour
period. The water vapor content in the atmosphere rose steadily
from dawn until noon. This water could have been brought into the
area from another region by the wind, or the haze or dust in the
air could have affected the instrument's measurements. Whatever
the cause for the change, the increase would be considered minute
when compared to Earth's atmosphere with 1000 times as much
moisture. 22
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- During the Viking primary mission, the
Martian water vapor underwent a gradual redistribution, the
latitude of the maximum amounts moving from the north polar region
toward the equator. Interestingly, while the amounts of vapor at
some latitudes changed dramatically, the total global water
remained almost constant at the equivalent of about one cubic
kilometer of ice. The largest amounts observed were found over the
dark polar region, which is inaccessible to Earth-bound observers.
Maximum vapor column abundances of about 100 precipitable
micrometers were measured adjacent to the residual cap itself-a
very large amount considering the temperature of the surface and
atmosphere in this region." The Mars atmospheric water detector
also confirmed the conclusion that the residual cap is made of
frozen water and that the atmosphere above it is saturated with
vapor during the polar summer. 23
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- Orbital science investigations had given a
better grasp of the global nature of Mars, and the entry science
experiments provided the first direct measurements of the physical
and chemical composition of the planet's atmosphere. The
scientists were for the first time "getting their hands on" some
more tangible data. Entry science investigations consisted of
measurements by the retarding potential analyzer, the
upper-atmosphere mass spectrometer, lander accelerometers, the
aeroshell stagnation-pressure instrument, and the recovery
temperature instrument. The analyzer had been designed to study
the nature of the ionosphere. The mass spectrometer was to provide
mass spectra for the constituents of the upper atmosphere.
[375] Three of
the instruments-the lander accelerometers, the aeroshell
stagnation-pressure instrument, and the recovery temperature
instrument-made up the lower-atmosphere structure experiment,
which measured the density, temperature, and pressure profile of
the atmosphere as the lander approached the surface. As with other
experiments and Viking hardware, the entry investigations had been
based on the common "Mars engineering model" adopted early in the
project. That model described the nature of the planet as it was
believed to be, from the best knowledge then available. As Jerry
Soffen recounted, the model was developed to set the boundaries
for design, prescribing the atmospheric envelope, the variety of
possible surfaces, range of textures, radiation environment, etc.
This "working manual" was constantly reviewed by scientists both
within and outside the project and used by all the engineers. The
Mars engineering model "was an excellent crossroads for scientists
and engineers," With the mission definition, it "truly spelled out
what we were trying to do and the planetary constraints we
believed existed." 24
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- The lander's mode of descent altered
several times before touchdown, and the entry instruments operated
during different phases of the entry process. At separation, the
lander capsule-consisting of the aeroshell and basecover
surrounding the lander-was deorbited by ignition of the deorbit
engines. The capsule began the first part of its descent
trajectory through the undisturbed interplanetary medium of ions
and electrons. The interplanetary medium streams away from the sun
at hypersonic velocities in what is called solar wind. Closer to
the planet, the lander capsule passed through a disturbed region
where the solar wind is diverted to flow around and past Mars,
Beneath this zone of interaction lay the Martian ionosphere, a
region of charged atomic particles. It was in the ionosphere, 3
minutes after the completion of the deorbit burn, that the
retarding potential analyzer began 18 sampling sequences, during
which 71 seconds of data were collected.
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- Entry
has been arbitrarily defined as starting at 250 kilometers,
although the atmosphere is only readily apparent from about 91
kilometers. From separation to entry required about 3 hours. At
entry, the lander capsule was oriented with the aeroshell and its
heatshield facing the direction of travel; before the atmosphere
exerted an appreciable drag, the capsule would accelerate to about
16000 km per hour. Almost l hour before the lander reached the
250-km mark, the upper-atmosphere mass spectrometer was turned on
for a 30-minute warmup period. The spectrometer and the retarding
potential analyze would continue to take measurements until the
capsule system sensed 0.05 gravity, at which time they would
shutdown. The capsule-mounted temperature sensor was then
deployed. With pressure sensors (deployed 10 minutes before
entry), it would continue to function until the aeroshell was
jettisoned (12 seconds after the radar altimeter sensed an
altitude of 5.9 km).
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- At about 27 km above the surface, the
capsule reached its peak deceleration and for a time its path
leveled off into a long glide, because of the
[376] aerodynamic
lift provided by the aeroshell. As the effects of atmospheric
friction and gravity overcame the lift, the capsule resumed
descent. By the time its radar altimeter indicated an altitude of
6.4km per hour, the capsule was traveling slowly enough (an
estimated 1600 km per hour) to deploy the parachute. Seven seconds
later, the aeroshell separated from the lander, and the remaining
lift in the lightened aeroshell permitted it to drift well away
from the landing site. Twelve seconds after aeroshell separation,
the lander legs were deployed, at which time the footpad
temperature sensor began collecting data, doing so until
touchdown. 25
-
- From the retarding potential analyzer, new
information about the Martian ionosphere was collected through
measurements of the solar wind electrons and ionospheric
electrons, the temperatures of the electrons, and composition,
concentrations, and temperatures of positive ions. At the higher
altitudes, the analyzer examined the interaction of the solar wind
and the upper atmosphere. The planet's weak (or non-existent)
magnetic field permits the solar wind to penetrate closer to the
surface of Mars than its does to Earth's surface. Data obtained
during descent indicates that singly ionized molecular oxygen
(O2+) is the major element of the upper atmosphere,
with peak concentration at an altitude of 130km. Singly ionized
molecular oxygen is about nine times as abundant as singly ionized
carbon dioxide (CO2+), the primary
ion produced by the interaction of sunlight with the Martian
atmosphere. This new finding lends support to theoretical analyses
by M. B. McElroy and J.C. McConnell, which call attention to the
reaction of atomic oxygen with CO2+ that would
produce carbon monoxide and the more stable ion O2+. The temperature
of the observed ions at 130km was about -113°C.
26 Viking measurements of O+ ions moving away from the
planet coupled with Mariner 9
observations of hydrogen escaping
from the planet's upper atmosphere suggest that the planet has
been losing the basic ingredients for water for billions of years.
Perhaps some of the water that once carved the massive channels on
the surface of Mars slowly escaped in the form of ionized hydrogen
and oxygen.
-
- The upper-atmosphere mass spectrometer
obtained data about the identities and concentrations of the
various gases from 230 to 100 km. As expected, the main
constituent of the upper atmosphere is carbon dioxide, with small
amounts of nitrogen, argon, carbon monoxide, oxygen, and nitric
oxide. Taken together, what do these upper atmospheric
measurements suggest? The discovery of nitrogen was a particularly
pleasant surprise. As Tobias Owen of the nuclear analysis team
commented, the search for nitrogen in the Martian atmosphere goes
back several decades, and he was "delighted" that they finally had
found it. When he first became interested in Mars during the
1950s, "it was an established doctrine that the pressure on Mars
was eighty-five millibars, plus or minus three millibars, and that
the atmosphere was well over ninety-five percent nitrogen.'' As
time passed, predictions changed; both the surface pressure and
the amount of nitrogen decreased. As the estimated amount of
carbon dioxide grew to more than 95 percent of the gas in the
atmosphere, detection of any nitrogen
[377] seemed
unlikely. This outlook was disheartening to the exobiologists who
believed that nitrogen was an essential ingredient in any
environment in which life might have evolved. But the
upper-atmosphere mass spectrometer did detect nitrogen. Happily,
Toby Owen said, "And now we finally got it; it's really there."
27
-
- Michael McElroy of the entry science team
went even further. According to him, Mars was a very "cooperative"
planet, and it had given the Viking scientists some bonus
information. Beyond defining the chemical composition of the
atmosphere, they discovered some "clues as to the evolution of the
planet from its isotopic abundance." Mars has more of the heavy
form of nitrogen than does Earth, which allows specialists to
theorize that Mars is "remarkably Earth-like although it has gone
through a different evolutionary history." McElroy explained that
there are two abundant isotopes of nitrogen: Mass 14, which is the
common form, and Mass 15, which is less common. They are both
present in Earth's atmosphere and in the Martian atmosphere, but
Mars has rather more of the heavy component than does Earth. The
implication is that Mars must have lost the light material over
time. The initial amount of nitrogen on Mars was apparently
similar to the initial amount on Earth, but slightly lower gravity
on Mars allowed the lighter nitrogen to escape. Perhaps Mars has
"evolved to a larger extent than the Earth because of this escape
process." 28
-
- While the presence of 2.5 percent nitrogen
in the atmosphere opened the door for speculation about
possibilities of organic material, the levels of argon led to
other theories, some of which were contradictory to the one used
to explain the presence of nitrogen. Argon was measured at 1.5
percent, considerably less than indicated by the indirect
measurements made by the Soviet Union with its Mars 6 mission in
1974. The discovery that Soviet scientists were mistaken was
welcome to Klaus Biemann and his colleagues on the molecular
analysis team, because it relieved their worry that argon might
choke the gas chromatograph-mass spectrometer. The low amount of
argon in the atmosphere would not prevent that instrument from
performing a series of atmospheric analyses units way to the
surface before it could be contaminated by organic compounds from
the Martian soil. 29
-
- A low concentration of argon also had
significant implications when it came to reconstructing the early
Martian atmosphere. The two common isotopes of argon are argon-36
and argon-40. The former is an inert element produced in the
interior of stars such as our sun, and the latter is created
during the radioactive decay of potassium-40. Both isotopes have
been released over time from the rocks of planets, and it is
generally held that the relative amount of the two says something
about how the atmosphere evolved. For Mars, this theory poses some
interesting problems and questions. Toby Owen proposed the
following scenario during a 28 July 1976 Viking science symposium
at JPL. Using the Earth's atmospheric history as a guide, Owen
argued that one could by analogy plot the evolution of the Martian
atmosphere hack over time. One way to make this analysis for the
two planets was to use argon-36 as the common piece of
information. It was [378] assumed
that Earth and Mars were formed at the same time and from the same
inventory of gases in the solar nebula. If that is true, then
Earth and Mars should have about the same ratio of argon-36 and
argon-40 in their atmospheres. They do not. Earth is relatively
poor in argon-36; it is held that this gas was lost early in the
evolution of the terrestrial atmosphere. Scientists thought that
they could deduce from the amount of argon-36 in the Martian
atmosphere the gases that have been lost. Viking measurements
indicate that the planet should have lost 10 times the amount of
carbon dioxide and nitrogen now measured in the atmosphere. But
the loss was not out into space; it was hidden in some form on the
planet itself. Ten times the present amount of carbon dioxide
constitutes a considerable amount of material to hide. Owen
reported: "I'm suggesting that somewhere between land 10 times the
present amount of CO2 is missing on
Mars....and some fraction could still be present in the form of
CO2 trapped in the [polar] caps. The other part of this
reconstruction, which is interesting, is that it implies a couple
of tens of meters of water on the surface which must also be
sequestered somewhere." 30 The water could have become permafrost, but this
explanation disagrees with the theory that the water left the
planet in the form of ionized hydrogen and oxygen.
Although no general agreements have been
reached on how the upper atmosphere of Mars was formed, one point
seems certain: that atmosphere was significantly different in the
past. Just as the evolution of Earth's atmosphere helped determine
the nature of its environment, the evolution of Mars is linked
with the development of its atmosphere. As Jerry Soffen concluded:
"It appears that there was a considerably denser atmosphere in the
past, somewhere between 10 and 50 times the present value of 7.5
millibars at the surface. This denser atmosphere would account for
the possibility of the ancient river [beds] seen from the
orbiter." 31 Whatever explanation the scientific community comes
to accept, Viking has made two points very clear-the Red Planet's
environment has not been static, and in the past was very
dynamic.
-
- The lower atmosphere structure experiment
provided vertical profiles of the density, pressure, and
temperature of the atmosphere from an altitude of 90 km to the
surface. Accelerometers, part of the lander's inertial reference
unit, acted as sensors for the initial measurements from which the
density profile was derived. The profile was determined by
observing the retardation of the capsule's descent by atmospheric
drag. Pressure and temperature measurements came at first from the
two instruments in the aeroshell. Because of the high initial
velocities of the lander capsule, the pressure sensor determined
the pressure of the atmospheric molecules against the aeroshell
surface; the actual pressures were determined analytically later.
In a similar fashion, the temperature probe, near the outer rim of
the aeroshell, measured the temperature of molecules flowing
around the aeroshell. During the parachute phase of the descent,
after the aeroshell had been jettisoned, the lander's pressure and
temperature sensors provided this information.
-
- [379] Altitude
data for construction of profiles came from the radar altimeter. A
by-product of the radar altimeter measurements was information
about the terrain beneath the lander. The terminal descent and
landing radar system, which controlled the very last stage of the
landing, also measured the extent to which the lander drifted
because of winds above the point of touchdown. Pressure and
temperature variations were measured by the two landers at
selected intervals during the descent (table 53). The temperature
in the region between 200 and 140 km above the surface averaged
about -93°C; for the region between 120 and 28 km it was -
l30°C. At touchdown, the Viking
1 atmospheric temperature was
about -36°C, and Viking 2
's reading was -48°C.
32
-
-
-
Table 53
|
- Structure of Martian
Atmosphere
|
.
|
.
|
Viking 1
|
Viking 2
|
.
|
- Altitude
|
Pressure
|
Temperature
|
Pressure
|
Temperature
|
(km)
|
(mb)
|
(°C)
|
(mb)
|
(°C)
|
.
|
120.0
|
0.000 004 14
|
- 136.85
|
0.000 001 99
|
- 157.15
|
108.0
|
0.000 018 40
|
- 126.75
|
0.000 013 00
|
- 152.05
|
96.0
|
0.000 080 20
|
- 127.25
|
0.000 066 00
|
- 122.95
|
84.0
|
0.000 387 00
|
- 128.95
|
0.000 288 00
|
- 131.75
|
72.0
|
0.002 050 00
|
- 134.05
|
0.001680 00
|
- 142.25
|
60.0
|
0.009 110 00
|
- 127.65
|
0.008 540 00
|
- 135.85
|
48.0
|
0.044 500 00
|
- 124.55
|
0.039 200 00
|
- 102.45
|
36.0
|
0.198 000 00
|
- 107.05
|
0.158 000 00
|
- 108.75
|
28.0
|
0.483 000 00
|
- 89.35
|
0.404 000 00
|
- 99.95
|
4.5
|
5.160 000 00
|
- 51.05*
|
5.222 000 00
|
- 51.95
|
4.0
|
5.390 000 00
|
- 50.53
|
5.483 000 00
|
- 51.55
|
3.5
|
5.635 000 00
|
- 48.45
|
5.747 000 00
|
- 51.05
|
3.0
|
5.885 000 00
|
- 46.65
|
6.015 000 00
|
- 50.55
|
2.5
|
6.150 000 00
|
- 44.85
|
6.282 000 00
|
- 50.05
|
2.0
|
6.427 000 00
|
- 43.05
|
6.564 000 00
|
- 49.55
|
1.5
|
6.707 000 00
|
- 41.35
|
6.853 000 00
|
- 49.15
|
1.0
|
6.994 000 00*
|
- 39.45*
|
7.160 000 00*
|
- 48.55*
|
0.5
|
7.301 000 00*
|
- 37.65*
|
7.480 000 00*
|
- 48.05*
|
0.0
|
7.620 000 00*
|
- 35.85*
|
7.820 000 00*
|
- 47.55*
|
-
- *Extrapolated.
-
- SOURCE: Alvin Seiff and Donn B. Kirk,
"Structure of the Atmosphere of Mars in Summer at Mid-Latitudes,"
Journal of Geophysical Research 80 (30 Sept. 1977): 4367, 4371.
-
-
-
- [380] Compared to
the scientific instruments aboard the orbiter or the lander, the
entry experiments were very short-lived. They operated only during
the descent to the surface. Still, these instruments provided
investigators with several new insights into the Martian
environment and clues that, when coupled with orbital and lauded
data, would help frame new hypotheses about the evolution of the
planet.
-
- As interesting as the orbital pictures and
measurements were and as informative as the entry data instruments
were, the best was to come. Science aside for a moment, the
reception of the first pictures from the lander cameras had to be
the most exciting event for many project participants, scientists
and engineers alike. For the public, the surface pictures were
certainly the main event.
-
-
ON THE SURFACE
-
-
-
- The first lander's first picture, of
footpad 3 (a 60° high-resolution image), demonstrated to
everyone that the craft was safely down on the surface. Minutes
later, camera 2 began taking a real-time picture, a 300°
panoramic view of the scene in front of the lander. These shots
had been planned to provide the maximum amount of immediate
information so that images of value would already have been
collected should something unforeseen terminate the operation of
the lander. Thomas A. Mutch, lander imaging team leader, recalled,
"The planning for these first two frames was exhaustive.''
Characteristically, everyone had some advice about the best
photographs to take. More than a year before the landing, team
members had been called to Washington to brief NASA Administrator
James Fletcher on camera strategy. "In the event of a botched
landing, the first two images might constitute our only pictorial
record of Mars." The pictures would be sent to the orbiter in the
first 15 minutes after landing and thence to Earth. Not for 19
hours, including the first night on Mars, would it be possible to
communicate again with the lander.
-
- Some of Mutch's associates argued with the
decision to photograph the footpad and then the view in front of
the lander. One challenged, "If you were transported to an unknown
terrain, would you first look down at your feet?" Mutch had to
agree that the common mental image of the explorer was that of an
individual shading his eyes with his hand looking far away to the
horizon. He records that his counter argument was rather
pedestrian. He thought-in the terms of a photogeologist-that the
first picture of the footpad would he technically the better of
the two:
-
- A primary photogeologic goal, perhaps
because it is so easily quantifiable, is increase in linear
resolution. Looking straight down, the slant range was abut 2 m
yielding a linear resolution of approximately 2 or 3 mm. Looking
toward the horizon, nominally 3 km distant, the linear resolution
would have been reduced toward two or three orders of
magnitude.
-
- Our logic would have been persuasive if
the surface of Mars had been generally flat, but covered with
small objects of unusual form. As it turned
[381] out, this
was not the case. The rock-littered surface in the near field is
relatively undistinguished. But the undulating topography and
diverse geology of the middle and far field is spectacular. From
both an exploratory and scientific perspective, the panorama to
the horizon is the more impressive of the first two pictures.
33
-
- This self-effacing evaluation is
characteristic of many of the Viking scientists, but especially of
Tim Mutch. Seated in the "Blue Room" as the first electronic
picture data began appearing on the television monitors throughout
the Jet Propulsion Laboratory facilities, Mutch in almost a boyish
manner commented, "The neat thing about pictures is that everyone
can do their own analysis. We're really quite superfluous here."
The images from the lander were reconstructed, picture element
(pixel) by picture element from left to right, just as they had
been taken by the camera on Mars. After going through the decoding
process in the ground reconstruction laboratory, the image was
shown throughout JPL a few lines at a time. From left to right,
the first pictures of Mars began to evolve on the monitors.
Reactions were varied, but nearly all were happy ones. For Tim
Mutch, it was "a geologist's delight." Jim Martin saw the first
picture in very practical terms-Viking was so far a success. He
expressed his appreciation to the entire Viking team and to the
"10,000 people across the country who deserve a part of the credit
given to me." Mission Director Tom Young was also pleased with the
performance of his spacecraft. As for the pictures, he said,
"quality was consistent with what we should get, but they have
exceeded my expectations." The quality was very good, and Young
added that "Mars has demonstrated that it is photogenic!"
34
-
-
- The Colors of Mars
-
-
- The first two photos of Mars received on
20 July 1976 were followed by a color photograph on the 21st. A
lot of people would not forget that first color picture. Mutch
tells the tale as well as anyone. During the first day following
the early morning lauding of Viking
1 , his team was preoccupied with
analysis and release of those first two images, "which, in quality
and content, had greatly exceeded our expectations." So much were
they concentrating on the black and white pictures, that they were
"dismally," to use Mutch's word, "unprepared to reconstruct and
analyze the first color picture." Mutch and his colleagues on the
imaging team had been working long hours, along with everyone
else, during the search for a landing site. Despite enthusiasm,
people were tired. Many of the Viking scientists in the upcoming
weeks would have to learn to present instant interpretations of
their data for the press. For the first color photograph, haste
led to processing the Martian sky the wrong color.
-
- In a general fashion, Mutch and his team
understood that a thorough preflight calibration of the camera's
sensitivity to the colors of the spectrum was necessary. They also
knew that they would need computer software programs to transform
the raw data efficiently into an accurate color....
-
-
[382]
The first photograph (above) from the
surface of Mars, taken minutes after the Viking 1 lander touched down
on 20 July 1976. Center of the image is about 1.4 meter from the
lander's camera no.2. Both rocks and finely granulated material are
visible. Many foreground rocks are flat with angular facets. Several
larger rocks have irregular surfaces with pits, and the large rock at
top left shows intersecting linear cracks. A vertical dark band
extending from that rock toward the camera may have been caused by a
one-minute partial obscuring of the landscape by clouds or dust. The
large rock in the center is about 10 centimeters across. At right is
a portion of the spacecraft's footpad, eith a little fine-grained
sand or dust deposited in its center at landing.
Below is the first panoramic view by Viking 1 on the surface. Horizon
features are about 3 km away. A collection of fine-grained material
at left is reminiscent of sand dunes. Projections on or near the
horizon may be rims of distant craters. Some of the rocks appear to
be undercut on one side and partially buried by drifting sand on the
other. The housing of the sampler arm, not yet deployed, and the
low-gain antenna are at left. In the right foreground are the color
charts for camera calibration, a mirror for the magnetic properties
experiment, and part of a grid on top of the lander body. At upper
right is the high-gain antenna for direct communication between the
lander and Earth.
-
-
- [383]....representation. "What we failed to appreciate
were the many subtle problems which, uncorrected, could produce
major changes in color. Furthermore, we had no intimation of the
immediate and widespread public interest in the first color
products-for example, intuitively corrected color images were
shown on television within 30 minutes following receipt of the
data on Earth." Although they resisted at first, the lander
imaging team was obliged to release the first color prints within
8 hours of having received the image. 35
-
- Instinctive reactions and intuition can
lead to mistakes when dealing with an alien world. Here is Tim
Mutch's first public reaction to the color photograph:
-
- Look at that sky-light blue sky-reddish
hue. It's a very exciting thing to see this distinct reddish
coloration to the surface. These are subtle hues. It's a
geological scene, a natural scene. Even in the deserts here on
Earth the reds are not crayon reds as painted by a child. This is
a surprisingly terrestrial-like desert scene. 36
-
- But to borrow Carl Sagan's phrase, to see
this picture in terms of deserts on our own planet was an "Earth
chauvinism." The photo was of Mars, not of Earth; the sky should
have been red. When James A. Pollack of the imaging team told a
press conference on July 21 that the Martian sky was pink, he was
greeted with some friendly boos and hisses. Sagan, in a way that
only he could, chided the newspeople the following day: "The sort
of boos given to Jerry Pollack's pronouncement about a pink sky
reflects our wish for Mars to be just like the Earth."
37
-
- There were three sensors with blue, green,
and red filters in the focal plane of the camera to record the
radiance of the scene in blue, green, and red light. The
multilayer, interference filters used in the lander cameras
(filters that could withstand the rigors of sterilization) have an
irregular spectral response. The blue channel, for instance,
responds slightly but significantly to light in the infrared
portion of the spectrum. The unwanted part of the signal must be
subtracted, "so that the absolute radiances at three specific
wavelengths in the blue, green and red are represented."
Subsequently, color prints were produced by exposing conventional
color film to [384] individually modulated beams of blue, green,
and red laser light, scanning the film with the same geometry
employed in the camera.
-
- Before the flight, the cameras had been
calibrated and the sensitivity of each sensor-filter combination
determined. "Qualitative tests indicated that simple normalization
of the voltages for the three color channels was sufficient to
produce reasonable color images. In making that judgment our
attention was generally directed to saturated colors in the
natural scene and test target." When the first color data were
received, Mutch's specialists used the same normalization
techniques to calibrate the image. "The result was surprising and
disquieting. The entire scene, ground and atmosphere alike, was
bathed in a reddish glow. Unwilling to commit ourselves publicly
to this provocative display, we adjusted the parameters in the
calibration program until the sky came out a neutral gray." The
soil and rocks demonstrated good contrast, and the colors "seemed
reasonable." This was the picture released eight hours later. "But
in our chagrin," Mutch recalled, "the sky took on a bluish hue
during reconstruction and photo-reproduction. The media
representatives were delighted with the Earth-like colors of the
scene."
-
- While the television and newspaper
reporters hurried to get this color print before their respective
audiences, continued analysis supported the reality of an orangish
tint throughout the scene. The atmospheric coloration was due to
the presence of suspended soil particles in the thin air. Mutch
recalled: "Several days after the first release, we distributed a
second version, this time with the sky reddish. Predictably,
newspaper headlines of Martian sky turns from blue to red were
followed by accounts of scientific fallibility. We smiled
painfully when reporters asked us if the sky would turn green in a
subsequent version." Experience with color imaging over the next
year indicated that the colors of Mars might vary, but the sky
would retain its reddish hue. "In summary," Mutch said, "the color
of the Martian scene, perceived by the necessarily abnormal eyes
of Viking, is elusive. In response to the inevitable question: `Is
that exactly how it would look if I were standing on Mars?' a
qualified `yes' is in order." 38
-
-
- A Real World
-
No matter what the color of the sky, the
Viking pictures created a new reality for many people. Jerry Soffen
said that, if any one thing stood out in his mind, "Mars had become a
place. It went from a word, an abstract thought, to a real place."
Soffen doubted that he would ever have an adventure like climbing
Mount Everest, but he knew that it existed because other people had
been there and had taken pictures of it, just as people had been to
other extraordinary places on Earth. And now, their "guy" had made it
to Mars. "He was not a person, but he was a close friend." For many
associated with the Viking project, the lander had become
personified. "It is like a person invented by a committee. And we
sent him there and he did his thing....Before the Viking missions
Mars was a fictional or fantasy....
[385]
Two variations of the first color
photo from the Viking 1 lander, taken on the Mars surface 21 July
1976. The blue-sky version above was released the same day. Below is
the true red-sky version released 26 July. The red cast is probably
due to scattering and reflection from sediment suspended int he lower
atmosphere. To assist in balancing the colors, a photo was teaken of
a test chart mounted on the rear of the spacecraft and the
calibration then applied to the entire scene.
[386]
The two photographs above were taken
with the Viking lander camera during tests in the summer of 1974. At
the top is a panoramic shot from a site overlooking the Martin
Marietta Corporation factory in Denver. The lower photo was taken at
the Great Sand Dunes National Monument in southwestern Colorado. The
lander camera is a facsimile camera, different in design from the
television and film cameras which have been used on many space
missions. The field of view is not imaged simultaneously. Instead,
adjacent vertical lines are successfully scanned. Reflected light
from each of the "picture elements" in the line is recorded on a very
small photodiode in the focal plane of the camera. Twelve diodes are
available for use, each optimized for a different distance and a
different part of the visible near-infrared spectrum.
[387]
|
.
|
|
|
Photos permit comparison of
the color of the Viking lander on Mars (at left) and Earth
(above)- especially the orange cables. Tim Mutch used this
guide to show that the red-sky rendition of the Mars
landscape was the correct one. In the Earth photo, Jim
Martin stands beside the science test lander in the Von
Karman Auditorium at Jet Propulsion Laboratory.
|
[388]
Photos taken by the Viking lander
camera provide comparison of an Earth scene (above) and one on Mars
(below). In a photo taken near the Martin Marietta Denver facility
during tests in 1974, tan and reddish sedimentary rocks have been
tilted and eroded to form prominent cliffs. Data from three diodes
(blue, green, and red) were combined for the color picture. Colors
have not been balanced; the blue contribution is unnaturally large.
For mission photos, colors were carefully calibrated. The Martian
horizon stretches across nearly 200° in the composite of three
color photos taken 4 September 1976 (center), 5 September (right),
and 8 September (left). A thin coating of limonite (hydrated iron
oxide) colors the surface predominantly rusty red, although some dark
volcanic rocks can be seen. The horizon is flat because the photo has
been rectified to remove the effects of the 8° tilt of the
spacecraft.
-
-
- [389]....place-the
planet of Flash Gordon or some world peopled by Edgar Rice
Burroughs. School children learn about the orderly progression of
planets, and one of them has the same name as the world of many
science fiction dramas. One Mars had physical, scientific
properties like Earth; the other was a fantasy land. Now they
could think of Mars as a genuine world. The shift from an object
to be studied to a real place might not have been important
scientifically, but it was a big change intellectually.
39
-
- Soffen pointed out that his personal
involvement with the planet seas not unlike that of the other
Viking scientists. It had been eight years since the beginning of
Viking. With the landing, the investigators were hungry for every
bit of knowledge, any new speculation that would lead to a better
understanding of the nature of Mars. Before the first photographs
were received from the lander, Mars was more a scientific problem
than an actual planet. When scientists talked about atmospheric
conditions, they were describing numerical quantities that had an
engineering significance for the designers. But it was difficult
to think in terms of real clouds, real winds, real temperatures in
the way we discuss our own weather. As the science fiction writers
had built imaginary worlds on which their stories could take
place, the scientists too had created a Mars that seemed to fit
their assumptions. But the planet created from earlier known
scientific facts had very little similarity to the Mars that the
orbiter and lander cameras portrayed. Mars as a real place was
much more complex and interesting than any that had been conjured
up in the minds of scientists. The new Mars of Viking has as many
complicated processes at work as does Earth.
-
- Geologist Tim Mutch also had some personal
reflections on what they had found awaiting them on Mars:
-
- If you were to tell a geologist that you
were going to go out to two places on Earth with your little
Brownie to take one or two rolls of film at each locality and then
were to come back and from this interpret the history of the
planet, he would think you were out of your mind, the most absurd
thing he had ever heard of. In a sense it is. So one should not
overestimate the exclusive model that you can generate from
pictures.
-
- But one thing that could be said
definitively was that the terrain of Mars was not bland. A
complicated history is exposed particularly in the photographs
taken at the Viking 1
site. "From a geological point of
view, there is clearly a sequence of events
represented....involving fundamentally different processes-for
example, impact, wind, volcanic activity, possibly fluvial
activity and possibly ground ice."
-
- The specialists confirmed a diversity of
rock types on Mars, indicating several petrographic types; that
is, rocks that probably have different mineralogy and at least
have different texture. More boulders seem to be on the surface
than can be accounted for by impact processes; perhaps the
weathering of bedrock or the deposition of rocks by fluvial
mechanisms account for them. And the bedrock visible in the Viking
images indicates that some [390] process,
either fluvial or alluvial, is stripping off the soil to reveal
the rock. At the Viking 2
site, the rocks are more
homogeneous. "They are highly pitted, due to either volcanic
vesiculation or to some peculiar process we simply do not
understand," reported Mutch. Some scientists think Viking 2 landed on a
wide-spread, fine-grain sediment mantle- the polar mantle. The
boulders littering the scene were probably imposed, either as
broken lava flows or as ejected boulders from a nearby crater.
40
-
- Seeing another planet up close opened the
way for comparison of two evolving worlds. With the passing of the
romantic Mars and the gradual acceptance of the new Red Planet has
come both excitement and disappointment. Looking at a tangible
place is far more exciting than ruminations about abstract places,
but the absence of life was a blow to many who had hoped to
discover life or who had hoped that life might have had a chance
to evolve. The biological and organic investigations indicated
that the prerequisites for life on Mars were not evident at either
landing site. 41
-
-
SCIENCE ON MARS
-
-
-
- Weather
-
-
- When Viking touched down on the surface,
weather reports started streaming their way to Earth. Martian
weather was clear, cold, uniform, repetitious. Seymour L. Hess,
meteorology team leader, reported on conditions at Chryse Planitia
on sols 2 and 3: *
-
- Winds in the late afternoon were again out
of a generally easterly direction but southerly components
appeared that had not been seen before. Once again the winds went
to the southwesterly after midnight and oscillated about that
direction through what appears to be two cycles. The data ended at
2:17 PM (local Martian time) with the wind from the ESE, instead
of from the W as had been seen before. The maximum mean wind speed
was 7.9 meters per second (18 mph) but gusts were detected
reaching 14.5 meters per second (32 mph).
-
- The minimum temperature attained just
after dawn was almost the same as on the previous Sol, namely
-86°C....The maximum measured temperature at 2:18PM was
-33°C....This [was] 2° cooler than measured at the same
time on the previous Sol.
-
- The mean pressure was 7.83 mb, which is
slightly lower than previously. It appears that pressure varies
during a Sol, being about 0.1 mb higher around 2:00AM and 0.1 mb
lower around 4:00 PM. 42
-
- During the course of the Viking lander
experiments, Hess and his fellow meteorologists discovered two
interesting facts about Martian weather patterns. One was the
extreme uniformity of the weather, presumably....
-
-
-
[391]Table
54
|
Mars and Earth
Temperatures, 21 July 1976
|
.
|
|
Mars
|
Earth
|
United Sates
|
.
|
Lowest temperature
|
- 85.5°C
|
- 73.0°C
|
2.7°C
|
(Soviet Vostok Research Station,
Antartica)
|
(Point Barrow, Alaska)
|
.
|
Highest temperature
|
- 30.0°C
|
47.2°C
|
42.7°C
|
(Timimoun, Algeria)
|
(Needles, California)
|
-
-
-
- ....due to the Martian atmosphere, which
is much simpler than Earth's. The Red Planet has only very, very
small amounts of water vapor and no oceans-makers of extreme
weather on Earth. Earth's atmospheric and surface water contribute
substantially to the variability of its weather. The second
discovery was the seasonal variation of pressure. When Viking
first landed, its instruments detected a steady decrease in the
mean pressure from day to day. But in the extended mission, the
pressure at both landing sites reached its lowest value seasonally
and began to rise again. The Viking meteorologists think this
variation is due to the condensation of carbon dioxide on the
winter cap and its release as spring comes to the northern
hemisphere. This process would remove a major constituent from the
atmosphere at a certain rate, changing the pressure
accordingly.
-
- At the second Viking site, 48° north,
the temperatures dropped as expected during the Martian winter.
Early in the mission, the minimum temperature was about
-87°C, but during winter the minimum temperature at dawn was
- 118°C. Frost on the surface was first observed in
mid-September 1977. At the time, the second lander was recording
nighttime temperatures of -113°C, and a photo of the frost
was taken at -97°C. With winter, the wind speeds increased
slightly, especially at the Viking 1
site, with several interruptions
in what had been a regular pattern of wind....
-
-
Viking Lander's meteorology boom and
sensors in deployed configuration.
-
-
- [392]....direction.
There were several periods of northerly winds all day for several
days in a row, associated with temporary drops in
temperature-Martian cold fronts. Hess and his colleagues had
thought winter, with the fallout of carbon dioxide, would greatly
increase wind speeds and variability. There were some wind
directional changes and gusts, but no noticeable changes of
patterns in wind direction or speed were recorded.
43
-
-
- Hardware Problems
-
-
- While Hess and his meteorological
colleagues began to compile weather data for the Viking 1 landing
site, other experimenters were having their difficulties. First,
the seismometer was nut functioning. Its seismic sensor coils had
been "caged" mechanically to prevent damage to these sensitive
components during the shock of landing. Following touchdown, a
fusible pin-pulling device was to have detonated, unlocking the
seismometer so it could begin full operation. For some reason,
perhaps a broken or misconnected wire, the fusible device failed
to work, and the instrument remained in the caged position. While
the Viking 2 seismometer performed satisfactorily, the
Viking 1 failure prevented the seismology team from locating
the approximate origin points of recorded seismic activity.
44
-
- Don Anderson and his colleagues on the
seismology team was afraid that the sensitive seismometer on
Viking would be hampered by the high winds on Mars. But during the
night from about 6 p.m. through the next morning, the winds die
down to about virtually zero and there are essentially no seismic
background noises. During that time, the seismometer can be
operated "at a very high sensitivity." Marsquakes as small as a
magnitude of 3 at a distance of about 200 kilometers can be
recorded. By comparing a Marsquake with a similar Earthquake, the
specialists estimated the mean crustal thickness at the Viking 2
landing site to be about 14 to 18 km, about half the thickness of
the crust in the continental parts of Earth and about 50 percent
greater than the average thickness of the oceanic crust. Viking
scientists think the crust on Mars may be as thick as
approximately 80 km, much thicker than the crust under continental
regions on Earth.
-
- An unexpected result of the seismic
experiment was a great amount of information about the winds on
Mars. A very sensitive wind detector, the seismometer picks up the
wind pressure on the lander, from which characteristics of the
wind can be determined. Like the meteorologists, the seismology
team detected the cold fronts. The wind pattern "changed very
rapidly on the 131st Martian day. The winds....started to blow all
night until 2 or 3 a.m. indicating a substantial change in the
weather patterns. If very high winter winds had continued at
night, they could have generated the massive dust storms we have
observed in the winter time." However, orbiter photographs have
shown only a few isolated dust storms, with none reaching the
magnitude of the planetwide dust storm of 1971.
45
-
- [393] Another
cause for concern for the Viking team appeared on the second day
of landed operations. The lander's UHF transmitter had been
designed to operate at three different power levels-1 watt, 10
watts, and 30 watts- depending on the rate of data transmission
required. During the relay-link portions of the mission, the
30-watt power level was scheduled for use, to permit the
transmission of the maximum amount of scientific data. From the
observed performance of the initial lauded relay link, confidence
in the system was high. During the first relay, approximately 30
million bits of data were transmitted to the orbiter, recorded,
and subsequently transmitted to Earth, all within a few hours
after the information left the surface of
Mars.** Success however, was short-lived.
-
- On 22 and 23 July, the UHF transmitter
switched over to the 1-watt power level without instructions to do
so. Tom Young told the press, "In the one-watt mode you can get
slightly over seventeen minutes' worth of data from the Lander to
the Orbiter." The mission had been designed so that slightly more
than l8 minutes of data would be transmitted to the orbiter as it
passed overhead, so the problem was not critical one, but it did
pose a vexing limitation. At the 30-watt level, the lander could
transmit telemetry to the orbiter for 30 to 32 minutes.
46
-
- On the morning of 24 July, the UHF
transmitter switched back to the 30-watt power level. Tom Young
reported this second mysterious power change at the news briefing
that day: "When we had the relay [of information] today, lo and
behold, it came up in the 30-watt mode, operating as we would like
for it to. So our statistics, to date, are two relay periods in
the 1-watt mode, two periods in the 30-watt mode. We are
continuing the analysis of this particular anomaly.
47 The radio specialists suspected that the problem
lay in the power-mode control-logic subassembly of the UHF
transmitter. To counteract this trouble, commands had been
prepared to order the guidance control and sequencing computer to
eliminate the electronic "noise" causing the problem. Before this
command was sent up, the transmitter switched back to the 30-watt
power level. The change supported the theory that the problem was
associated with noise susceptibility. Following the
self-correction, the UHF transmitter performed as expected until
one week before the end of Viking 1
's primary mission. At that time,
telemetry indicated that there were potentially new problems with
the 30-watt level. To avoid a catastrophic failure and to extend
the transmitter's life for use in the "follow-on'' mission, the
lander performance analysts decided to use the 10-watt power mode
for the last sols of the basic mission. 48
-
- The landed relay communications for
Viking 2 did not demonstrate ally anomalies. On sol 21 of
the second landed mission, orbiter I was moved into position over
lander 2 to provides relay link. This maneuver permitted mission
planners to send orbiter 2 on an extended "walk" around the
planet, to photograph the poles and other regions of Mars and scan
them [394] with the
infrared thermal mapper and the Martian atmospheric water
detector. Orbiter l continued to provide the communications link
for the second lander during the remainder of Viking 2 's primary
mission. 49
-
- A more serious problem emerged in the
first days after Viking 1
's touchdown when the surface
sampler arm became stuck. On Thursday, 22 July, the surface
sampler assembly was rotated so that the protective shroud
covering the sample collector head (scoop) could be jettisoned.
During this operation, the sampler boom was to be extended a few
centimeters and then returned to the stowed position. Extending
the boom was no problem, but on retraction it stuck. At first, Jim
Martin and crew thought the problem was one of electronics. At
6:30 p.m. on the 22d, Martin told reporters preliminary
indications were that perhaps the soil-sampler control
assembly-the receiver for computer commands-had "some kind of an
electronic problem." He could switch to a redundant soil-sampler
control assembly if that was the problem, but, "the concern I have
at the moment is that unless we can solve or understand this
problem and solve it in fairly short order we are likely to run
the risk of impacting the soil acquisition sequence on Sol 8."
50
-
- By 10 p.m. on the 22d, Martin's team had
arrived at a new theory. Prefacing his remarks to the media with,
"It has been a very busy day,'' Martin addressed the problem of
the sampler. Everyone knew that loss of the sampler would be a
major setback for Viking science activities. Without It, no
samples would be delivered to the biology instrument, the gas
chromatograph-mass spectrometer, or the x-ray fluorescence
spectrometer. Martin believed that his people, who had worked all
evening, had "isolated the most probable cause of the problem. It
turns out, contrary to my expectation, not to beau electrical
problem. "Instead, it was apparently a simple- if anything can be
simple when working with a piece of equipment millions of
kilometers away-mechanical hang-up. Martin pointed out "that there
is a locking pin that is part of the shroud latching system"; that
pin was supposed to drop to the Martian surface doting the boom
extension... It now appears that the extension that had been
commanded in the sequence was not long enough to allow this pin to
drop free."
-
- Martin bad observed a duplication of the
difficulty on the science test lander, which was housed in a
glass-walled room next to the auditorium in which the press
briefings were held at JPL. Commenting on the fishbowl atmosphere
in which his people had been working, Martin told the reporters,
"I went in and looked at it myself when some of you weren't
looking.'' The stuck pin was "certainly a plausible and possible
failure mode." To test this theory, "we plan to send up a new
command sequence on the Sol 5 command load which will go up at
around midnight Saturday night," 24 July. Mission analysts thought
that extending the boom to about 35 centimeters would let the pin
fall. Martin added, "If by some chance the pin was retained within
the mechanism, which really believe is doubtful, we don't ever
intend to retract it as far as we did in the original sequence."
That way. they would avoid another difficulty; at a certain point
the boom extraction motor would clutch on purpose and then shut
itself off to avoid [395] damage to
the motor. If the pin did not drop free this time, the boom would
be ordered to extend far enough so that the "no-go'' signal would
not be given. 51
-
- Two photographs taken by the lander camera
on sol 5, 25 July, showed that the retaining pin did fall free,
landing on the ground in front of the craft. 52 The apparent ease with which this problem had been
diagnosed and corrected hid the months of training and preparation
fur such mission operations. Subsequently, more serious troubles
were to plague the soil- sampler assembly, but each time training
and ingenuity permitted the team to work out solutions and keep
the mechanism functioning. Adaptability was one of the key
elements of Viking's landed operations.
-
-
- Communicating with the
Spacecraft
-
-
- Before separation from the orbiter, the
lander had been given an initial computer load (ICL, or "ickel"),
which contained all the computer commands necessary for a basic
60-day mission, even if there were no further communications from
Earth. With normal communications between the spacecraft and
mission control, the mission programmers could modify the initial
computer load as needed to get the most out of the lander.
Commands were "uplinked" to the lander from JPL through the
stations of the Deep Space Network to the orbiter and then to the
guidance, control, and sequencing computer. The command uplinks,
made in three-day cycles, were the responsibility of the lander
command and sequencing team of the lander performance and analysis
group.
-
- Agreeing on the commands to be sent to the
lander, programming them, and checking them out through
simulations was a complex series of tasks, which required a great
deal of work and interaction among many persons. An example is the
decision to photograph the sampler boom immediately after
acquisition of a sample. The requirement would first be sent to
the lander imaging team, which had three three-person squads who
handled such requests. These uplink squads, plus a "late-adaptive
squad" responsible for last-minute alterations, would investigate
the picture called for and determine if it could be combined with
others or if it had to be taken by itself. The series of pictures
for a given sol was then described and combined into a science
requirement strategy that was passed on to the Lander Science
Systems Staff, which had the difficult task of matching wants
(requirements) with the constraints imposed by the lander systems
and the other tasks that had to be accomplished.
-
- The Lander Science Systems Staff received
the uplink plans in the form of computer printouts called science
instrument parameters-specific commands to the guidance, control,
and sequencing computer. Lander Imaging had 56 commands available,
and each could be adapted to special requirements. Once approved
by the Lander Science Systems Staff, the parameters were passed on
to the lander computer simulations personnel, who ran through the
commands to see if there were any software or hardware...
-
-
-
- [396] Viking Surface Sampler
-
- The Viking lander's chemical and
biological investigations all used samples of surface materials
excavated by the surface sampler In addition, as the experience
with lunar Surveyor spacecraft demonstrated, there was much to
learn about the surface simply by digging in it. In the Viking
mission, digging was part of the physical properties and magnetic
properties investigations.
-
- The surface sampler consisted of a col
rector head attached to the end of a three-meter retractable boom.
The arm housing the boom could be moved both horizontally and
vertically. The boom itself was constructed from two ribbons of
stainless steel welded together along the edges. When extended,
the two layers opened to form a rigid tube. When retracted, the
boom flattened. A flat cable sandwiched between the boom layers
transmitted electrical power to the collector head.
-
- The collector head was basically a
scoop with a movable lid and a backhoe hinged to its lower
surface. Where the scoop is attached to the end of the boom, a
motorized rotator acted as a mechanical wrist to permit
manipulation of the collector head. To fill the scoop, the lid was
first raised and then the boom was extended along or into the
surface. Once full, the lid closed. The top of the lid had holes
two millimeters in diameter, which formed a sieve. When the
collector head was positioned over one of the inlets for the
instruments, it was inverted and vibrated. Only particles smaller
than two millimeters were delivered to the instrument inlets.
Coarser samples could be delivered to the x-ray fluorescence
spectrometer, if desired. The gas chromatograph-mass spectrometer
and the biologyinstruments had their own filters to control the
size of material introduced into their sample processing
assemblies.
-
- The surface sampler could also dig
trenches, by lowering the backhoe to place the sampler head on the
surface, and then retracting the boom. Excavated materials could
be scooped up for sampling. A brush, magnets, temperature sensor,
and other instrumentation also provide data concerning the
physical properties of the materials.
-
-
-
....conflicts. Considerations such as
electrical energy required or the thermal impact of a command were
also determined. Following simulations, the request was codified
into a "lander sequence." After all the necessary changes
(massaging) were completed, the command was entered into the
ground-based computer and relayed to the Deep Space Network for
transmission to Mars.
-
- Uplink teams preparing lander sequences
worked about two weeks ahead of the time the command was to he
executed. Changes could be made in the planned uplink until about
48 hours before it was loaded into the....
-
[397]
|
.
|
|
.
|
|
A premission photo, above,
shows how the surface-sampler collector head deposits its
contents into the biology-instrument processor and
distributor assembly. The collector head and the area of the
sampler arm's operation are sketched at right. Below,
project scientist Gerals Soffen examines the collector head
on the science test lander at JPL.
|
|
.
|
|
|
|
-
-
- [398]....computer.
Obviously, uplinking was a precise. demanding business. Mistakes
were totally inadmissible. Although out of the limelight, the
people responsible for talking with the lander had a difficult
task. Occasionally, nerves wore thin when the requirements of
different science teams conflicted. The uplinkers were expected to
satisfy everyone's needs. and for the most part they did.
53
-
-
- Sampling the Martian Surface
-
-
- Scientifically, the most important
experiments aboard the lander were those which sampled the
planet's surface. Of these, the chemical analyses were
interesting, but the biological experiments were a disappointment.
As with other investigations, Mars again turned out to be a more
complex riddle than anticipated and, while there is still
disagreement over the exact causes of some of the reactions
observed. most-but not all-of the Viking scientists have come to
the opinion that detection of life on Mars is a very unlikely
prospect.
-
- The first soil samples were acquired on
sol 8, 28 July. Four samples were dug, with the first being
deposited into the biology instrument distributor assembly, the
next two into the GCMS processor, and the fourth into the funnel
of the x-ray fluorescence spectrometer. All the commands were
successfully executed, but there was no positive indication that
the gas chromatograph-mass spectrometer processor had been
properly filled. A second acquisition attempt still did not
provide a "sample level detector `full' indication." The sampler
system, having completed its programmed sequences in a normal
manner, parked the boom as planned. On Earth, the lander
performance specialists began to analyze the possible causes of
the anomaly: (1) insufficient sample acquired in the collector
head because the same sample collection site had also been used
for the biology sample; (2) insufficient time allowed for the
sample to pass from the funnel through the sample grinding section
and then through the fine (300-micrometer) sieve into the metering
cavity of the instrument; (3) grinder stirring spring not
contacting the sieve; or (4) sample-level-detector circuit faulty.
Since the "level-full" detector consisted of a very fine wire
stretched across the cavity to which the sample material was
delivered, it was also possible that it had broken when the soil
was dropped into the funnel. 54
-
- An anomaly team headed by Joseph C.
Moorman, who had worked closely with the builders of the GCMS,
went to work on this problem. While preparations were made for
another sample to be collected on sol 14, 3 August, Martin and
Young had to decide whether to proceed on the assumption that the
GCMS had actually been filled and chance wasting one of the two
remaining ovens on an empty chamber (the specialists had
determined that one of the ovens was inoperable during the GCMS
in-flight checkout) or pick up another sample on sol 14.
Conservatism and caution argued for the latter decision, and the
managers chose that option. But the boom did not cooperate. It
jammed.
-
- [399] The
surface-sampler control-assembly sequences performed normally
through the 12th command. During the execution of the 13th (boom
retraction to 26.7 centimeters). trouble showed up; when the
computer issued the 14th command, the assembly would not respond.
Examination of photos taken on sol 14 revealed that the sampling
trench had been dug as ordered, but the collector head was not
over the GCMS funnel where it was supposed to be. An image
received on sol 15 showed the back of the boom. Three possible
reasons for this new anomaly were considered: (l) failure of the
surface-sampler control-assembly electronics; (2) failure of the
boom motor or related equipment; or (3) jamming of the boom,
precluding proper retraction. Causes 1 and 2 were rejected after
analyzing the proper performance through the first 12 commands.
Jamming had most likely caused the difficulty since the failure
appeared to be similar to the "no-go'' response encountered with
the sol 2 shroud-pin jam.
-
- Frozen carbon dioxide or surface material
were rejected as possible causes of jamming the boom, because of
the absence of a slowly increasing motor load, which the
investigators would have detected. Discussion of the anomaly with
the boom designers revealed that a similar problem had occurred
during early test phases, and they believed it was caused when a
series of successive retract (or extend) commands had been issued.
In testing, the successive commands tightened the boom element on
the storage drum, and the boom element tended to wind around the
drum in a 5-or 6-sided configuration rather than in a perfect
circle. This arrangement caused Intermittent high loading when the
"points of the hexagon" passed under the boom restraint brake
shoes. The reliability of the system was further weakened when
operated at low temperatures; the motor torque limiter finally
decoupled, and movement of the boom ceased. Two major operating
procedures were proposed to meet the problem: (I) All sequences
were to be revised to eliminate successive extend or retract
commands. avoiding excessive tightening of the boom element on the
drum. The command reversals would cause the extend or retract
"flip-flop" gear to disengage the load during each cycle, allowing
the motor to attain full speed and operating torque before it
reengaged the load in the opposite direction. (2) Future
operations were to be performed within one to two hours of the
peak temperature during the Martian sol. An uplink diagnostic
sequence was designed for sol 18; the boom would be used in each
axis of operation- extend, retract, up elevation, down elevation,
clockwise, and counter-clockwise. The sequence was executed
properly and no anomalies were met. Following Martin Marietta's
instructions, all activities of the sampler arm were redesigned
"to exclude, wherever possible. successive extend or retract
commands, and to perform these operations during the warmest part
of the sol." The Viking team had no further problems with the
sampler boom on either lander, and operating temperature
restrictions were eventually waived because of the need to acquire
early morning biology samples. Preflight testing and the
documentation of those procedures had paid off.
55
-
- [400] The sol 14
anomaly forced Martin and Young to reconsider their decision not
to analyze the "possible" sample acquired on sol 8. Influenced by
early results from the biology experiments, the molecular analysis
team urged that the contents of the gas chromatograph-mass
spectrometer be analyzed. Jim Martin and Tom Young agreed.
-
- Biology . At the 1:30 pm news briefing on 31 July 1976 (sol
11), Jim Martin made an announcement. Prefacing his remarks with.
"I wanted to state that it's been project policy for seven years
to make data available to the media when we have [them]," Martin
noted that this day was -no exception. We have received biology
data that we believe to be good data." Engineering telemetry
indicated that the biology instrument was performing "extremely
well," perhaps too well, since early reactions from the
gas-exchange and labeled-release experiments were very positive.
That could possibly be the consequence of biological activity, but
Martin was cautious: "I think Chuck Klein will continue to caution
you that the biology experiment is a complex one. We've seen that
Mars is a complex planet. There are many things that we do not
understand." The scientists were proceeding systematically and
methodically. 56
-
- Biology Team Leader Harold P. Klein and
his colleagues had already conducted a number of tutorials for the
news people covering the Viking mission, and at each session where
they presented analytical details they took time to explain the
experiment in question. The biologists started with the basics.
Each Viking Lander carried an integrated biology instrument, which
contained three experiments designed to detect the metabolic
activity of microorganisms should they be present in the soil
sampled. First, the gas-exchange experiment would determine if
changes caused by microbial metabolism occurred in the composition
of the test chamber atmosphere. Second, the labeled-release
experiment, also known as Gulliver, would determine if decomposed
organic compounds were produced by microbes when a nutrient was
added. Third, the pyrolytic-release experiment would detect, from
gases in the chamber, any synthesis of organic matter in the
Martian soil. A change could be the result of either
photosynthetic or nonphotosynthetic processes.
-
- On 31 July, Klein told the press: "What we
are proposing to do for you today [is] to give you a status report
on the three experiments and we'd like to then focus on one of the
experiments, the labeled release experiment, a little more closely
since some of that data is exciting and interesting." First, all
three instruments were working normally. "We have no anomalies, no
problems despite what some of the press or other news media have
said." He had heard rumors that the biology instrument was "sick,
dead in the water." The truth was that the instrument was in good
shape, and he had two important, unique facts.
-
- First, the gas-exchange experiment had
given them reason to believe that "we have at least preliminary
evidence for a very active surface material. . . . .We believe
that there's something in the surface, some chemical or
[401] physical entity
which is affording the surface material a great activity." But,
adding a word of caution, he noted that the reaction observed in
the gas-exchange experiment might be mimicking some aspects of
biological activity. Second, the labeled-release experiment's
radioactivity counters were measuring "a fairly high level of
radioactivity which to a first approximation would look very much
like a biological signal." The highly active nature of the soil,
however, caused the biology team members to be cautious. "That
second result must be viewed very, very carefully in order to be
certain that we are, in fact, dealing with a biological or
non-biological" phenomenon.
-
- Klein reported on the sequencing of the
three biology experiments. Norman Horowitz's pyrolytic-release
experiment had been started first. After the soil had been
injected into the test chamber and carbon 14- labeled carbon
dioxide added, the xenon lamp had been turned on; incubation would
last until at least sol 14, when the first results might be
available. Vance Oyama's gas-exchange experiment had also received
its soil sample on 28 July, but the incubation process was not
begun until the morning of the 29th, when the chamber containing
the soil and Martian atmosphere was injected with a mixture of
carbon dioxide, krypton, and half a cubic centimeter of nutrient.
About two hours later, gas in the chamber was analyzed-a
calibrating measurement against which all subsequent analyses
would be measured. Calling for the lights in the Von Karman
Auditorium to be turned off, Klein had a chromatogram based on the
first gas exchange results projected on the screen behind
him:
-
-
Biology instrument.
-
-
- [402] What we saw were
five peaks-little tiny peaks: neon, over here on your left and
that's explainable by the neon we used in the nutrient chamber
itself and that's our indication that we, in fact, injected
nutrient and that's fine- there's nothing unusual about that. Then
you see nitrogen and that amount of nitrogen can be accounted for
by the nitrogen in the atmosphere and a small amount of nitrogen
that we know was contaminating our CO2 krypton mixture.
Then we see this oxygen peak which I will come back to in a
moment. And then as a shoulder beside the oxygen, you see a small
peak and that's a combination of argon and carbon monoxide and
that amount of gas would be consistent with current estimates of
argon and carbon monoxide in the atmosphere.
-
- A large krypton peak, Klein explained, was
present because they had added krypton in a specifically known
amount to provide a standard reference for determining the amount
of other gases that might be present. He turned back to the oxygen
peak: "You will see at the base of that oxygen peak, a little
bar-that's the amount of oxygen down there that we can account
for, or could account for from all known sources in the atmosphere
or in the contamination of our gas mixture," But the instrument on
Viking 1 was indicating 15 times more oxygen than the
scientists could account for from known sources, The results from
the second measurement made 24 hours later showed that all the
gases had remained the same except oxygen. It had increased by 30
percent. After ruling out all other possible causes, the
scientists concluded that the oxygen had to be coming from the
soil itself. While one possible explanation for the increase was
biological activity, other explanations were possible, too.
57
-
- A possible alternative answer to why the
initial amount of oxygen had been released lay in the desert area
of landing site; the Martian samples contained peroxides and
superoxides, which when exposed to abnormal (non-Marslike)
humidity in the instrument quickly released oxygen. The related
release of carbon dioxide suggested that the samples had an
alkaline core. Although such reactions had not been witnessed on
Earth, the scientists believed that the intense ultraviolet
radiation bombarding the surface of the Red Planet could have
produced unique photocatalytic effects. Still, there was much to
be explained, including the reactions observed from the
labeled-release investigation.
-
- Gulliver was sending back some surprises.
As with the gas-exchange experiment, the labeled-release
experiment added a small amount of nutrient to the soil sample. It
also produced a large amount of gas after that injection. Where
the gas-exchange produced a spectrum of the gases, the labeled
release measured the amount of radioactivity produced by the
carbon- 14 -labeling" material in the nutrient. Shortly after the
addition of the nutrient, the radiation counts rose sharply,
leveling off at about 10,000 counts per minute.
-
- Gil Levin gave the audience at JPL a brief
resume of the activities since the injection of the nutrients,
which had occurred at about 1:45 p.m. PDT on
[403] 30 July. That
injection had consisted of about 0.1 milliliter, or about 2 drops,
of liquid. As Levin noted. "If any organisms are present that can
utilize the nutrient and if these organisms behave
biochemically-roughly as terrestrial organisms do-they should
imbibe the nutrient and exhale a radioactive gas." Resulting
radioactivity was measured periodically by a radiation detector.
The result on Mars was very interesting. It was similar to ones
encountered with living organisms detected in terrestrial soil,
but Levin warned, "We are far too early in the game to say that we
have a positive response." There were too many factors that had to
be weighed and tested. "All we can say at this point is that the
response is very interesting, be it biological or non-biological,
it is unanticipated."
-
- As in the gas-exchange experiment, there
was a possibility that the soil itself contained catalysts,
minerals, inorganics that produced some breakdown of the
radioactive compounds. "The effect of water introduced into the
dry Mars soil may cause violent chemical reactions that would
disintegrate a portion of our medium." As a consequence, Levin
thought that any speculation about the biological or
non-biological nature of the response would have to await further
data. 58
-
- By l August, the production of oxygen in
the gas-exchange experiment had decreased considerably, thus
supporting the belief that the release was the function of oxides
in the soil. In a 2 August update on the labeled-release
experiment, Levin noted that they had examined the radioactivity
curve very carefully. They had found no evidence of any doubling
of cells. No growth appeared to be taking place, but the curve did
not seem to behave as scientists would have expected it to for
chemical reactions either. "We find that the chemical reaction
took place at a very rapid rate initially, and then
uncharacteristically slowed down and took a long time to plateau."
The curve detected with the labeled-release experiment did not
agree with known responses for either chemical or biological
reactions. 59
-
- Data returned by the pyrolytic-release
experiment and reported by Norman Horowitz on 7 August were
equally confounding. Once again, the specialists had detected a
reaction, but they did not know what it meant. "There's a
possibility that this is biological," Horowitz said, but "there
are many other possibilities that have to be excluded." The
results obtained the night before were interesting but he
emphasized that they were not ready to say that they had
discovered life on Mars. "The data point we have is conceivably of
biological origin, but the biological explanation is only one of a
number of alternative explanations." He told the press:
-
- We hope by the end of this mission to have
excluded all but one of the explanations, whichever that may be. I
want to emphasize that if this were normal science, we wouldn't
even be here-we'd be working in our laboratories for three more
mouths-you wouldn't even know what was going on and at the end of
that time we world come out and tell you the answer. Having to
work in a fishbowl like this is an experience that none of us is
used to.
-
- [404] He also
cautioned the reporters that they were being included in the
analysis phase of the experiments. They were "looking over the
shoulder of a group of people who are trying to work in a normal
way in an abnormal environment." 60 The scientist's caution was prompted by his
knowledge that "we well might be wrong in anything we say. Anyone
who has carried out a scientific investigation knows that the
pathway of science is paved not only with brilliant insights and
great discoveries, but also with false leads and bitter
disappointments. And nobody wanted to be wrong in public on a
question as important as that of life on Mars."
61
-
- Later in a November 1977 Scientific
American article, Horowitz was able to speak more authoritatively
about the results that had been observed in all three experiments.
In the gas-exchange experiment, "the findings of the first stage
of the experiment were both surprising and simple." Immediately
following the addition of the moisture to the sample chamber-the
soil sample was not directly wetted-carbon dioxide and oxygen were
released. The evolution of gases was short-lived, but the pressure
in the chamber increased measurably. At the Chryse site, the
amount of carbon dioxide increased by about 5 times, and the
amount of oxygen increased by about 200 times in little more than
one sol. At the landing site in Utopia, the increases were smaller
but still "considerable." Upon reflection, Horowitz stated that
"the rapidity and brevity of the response recorded by both landers
suggested that the process observed was a chemical reaction, not a
biological one." Horowitz felt that the appearance of the carbon
dioxide was readily explainable: "Carbon dioxide gas would be
expected to be adsorbed on the surface of the dry Martian soil; if
the soil was exposed to very humid atmosphere, the gas would be
displaced by water vapor." The presence of the oxygen was logical
but harder to account for, since so much oxygen would seem to
require an oxygen-producing substance, not just the physical
release of preexisting gas. There was just not that much oxygen
available in the atmosphere-past or present-to account for the
quantities measured. Horowitz argued that it was "likely that the
oxygen was released when the water vapor decomposed an oxygen-rich
compound such as a peroxide. Peroxides are known to decompose if
they are exposed to water in the presence of iron compounds, and
according to the X-ray fluorescence spectrometer....the Martian
soil is 13 percent iron."
-
- At both sites, the second phase of the
gas-exchange experiment was "anticlimactic." When the sample was
saturated with the aqueous nutrient, more carbon dioxide and
oxygen were produced. The additional evolution of carbon dioxide
was probably a continuation of the reaction observed in the humid
stage of the experiment. Horowitz believed that the amount of
oxygen then diminished because of its combination with the
ascorbic acid in the nutrient medium. "And so....it became clear
that everything of interest happened in the humid stage of the
experiment, before the soil came in contact with the nutrient!"
Thus, in November 1977, Horowitz confidently stated that the
gas-exchange experiment had detected "not
[405] metabolism but
the chemical interaction of the Martian surface material with
water vapor at a pressure that has not been reached on Mars for
many millions of years." 62
-
- In the labeled-release experiment, there
was a similar rapid surge of gas into the test chamber when the
nutrient solution was added to the soil. This release tapered off
shortly after the passage of one sol. Horowitz noted, "The gas,
undoubtedly carbon dioxide, was radioactive, showing that it had
been formed from the radioactive compounds of the medium and not
from compounds in the Martian soil." He also believed that other
nonradioactive gases were evolved when the water in the nutrient
medium came in contact with the sample, but that these could not
be detected by the instrument. "The production of radioactive
carbon dioxide in the labeled-release experiment is understandable
in light of the evidence from the gas-exchange experiment
suggesting that the surface material of Mars contains peroxides."
Formic acid, which was one of the compounds in the labeled-release
nutrient, is oxidized with relative ease. "If a molecule of formic
acid (HCOOH) reacts with one of hydrogen peroxide
(H2O2), it will form a molecule of carbon dioxide
(C02) and two molecules of water (H20)." The amount of
radioactive carbon dioxide produced in the experiment was only
slightly less than would have been predicted if all the formic
acid in the nutrient had been oxidized in this manner.
-
- Going a step further with his analysis,
Horowitz said that if the source of the oxygen in the gas-exchange
experiment was peroxides in the soil decomposed by the water
vapor, then the labeled-release experiment should have decomposed
all of the peroxides with the first injection of nutrient, The
second injection should have produced no additional radioactive
gas. That was what happened. "When a second volume of medium was
injected into the chamber, the amount of gas in the chamber was
not increased; indeed, it decreased. The decrease is explained by
the fact that carbon dioxide is quite soluble in water; when fresh
nutrient medium was added to the chamber, it absorbed some of the
carbon dioxide in the head space above the sample."
-
- In the labeled-release experiment, the
stability of the reaction to heating at various temperatures was
examined. Heating reduced and subsequently stopped the reaction.
This result has been interpreted by some to be evidence in favor
of biological activity, but Horowitz, although conceding that the
effects of heating could be explained by biological activity, said
that these results were also consistent with a chemical oxidation
in which the oxidizing agent is destroyed or evaporated at
relatively low temperatures. "A variety of both inorganic
peroxides and organic peroxides could probably have produced the
same results." 63
-
- The third biology experiment, pyrolytic
release, differed from the others in two basic respects. First, it
attempted to measure the synthesis of organic matter from
atmospheric gases rather than the decomposition of that matter.
Second, it was designed to operate under pressure, temperature,
[406] and atmospheric
composition that were nearly the same as those on the planet.
During the actual operation of the pyrolytic-release
investigation, the temperatures ran higher than those normally
encountered on Mars because of heat generated within the lander. A
sample of the soil was sealed in the test chamber along with some
of the planet's atmosphere. A xenon arc lamp simulated the sun.
Into this Martian microcosm, small amounts of radioactive carbon
dioxide and carbon monoxide were introduced. After five days, the
xenon lamp was turned off, and the atmosphere was removed. The
soil was then analyzed for the presence of radioactive organic
matter.
-
- Analysis of the soil began with heating it
in the pyrolyzing furnace- hence, the name pyrolytic release-to a
temperature high enough to reduce any organic compounds to small
volatile fragments. Those "fragments were swept out of the chamber
by a stream of helium and passed through a column that was
designed to trap organic molecules but allow carbon dioxide and
carbon monoxide to pass through." In this process, radioactive
organic molecules would be transferred from the soil to the column
while being separated from the remaining gases of the incubation
atmosphere. Any organic molecules would be released from the
column by raising the column's temperature. Simultaneously, the
radioactive organic molecules would be decomposed into radioactive
carbon dioxide by copper oxide in the column and transported to
the radiation counter by the helium carrier gas. If, as a result
of this process, organic compounds had been formed, there would be
detectable radioactivity; if there were no organics, there would
be no radioactivity.
-
- Horowitz noted that, surprisingly, "seven
of the nine pyrolytic-release tests executed on Mars gave positive
results." The negative results occurred with samples obtained at
Viking 2 's Utopia site. The amount of radioactive carbon
dioxide obtained by the experiment was small; still, it was enough
to furnish organic matter for between 100 and 1000 bacterial
cells. Significantly, "the quantity is so small....that it could
not have been detected by the organic-analysis experiment," the
gas chromatograph-mass spectrometer (see below). Though small, the
quantity was important, because as Horowitz expressed it, "it was
surprising that in such a strongly oxidizing environment even a
small amount of organic material could be fixed in the soil." Even
more important to him was the fact that "the pyrolytic-release
instrument had been rigorously designed to eliminate
non-biological sources of organic compounds." To encounter
positive results from the Martian soil in spite of all the
precautions was in the biologist's word "startling."
-
- However, on reflection, it appeared that
the findings of the pyrolytic-release experiment had to be
interpreted non-biologically. The reaction did not respond to heat
in a manner consistent with a biological reaction. Martian
microbes, accustomed to the very low temperatures on that planet,
would have been killed by the elevated temperatures experienced
during the test, the investigators thought. "On the other hand, it
is not easy to point to a non-biological explanation for the
positive results." Investigations into
[407] this curious
reaction have continues in terrestrial laboratories, and until
"the mystery of the results. . . .is solved, a biological
explanation will continue to be a remote possibility."
64
-
- Gas Chromatograph-Mass Spectrometer
(GCMS) . While the results of the
biology experiments did not seem as bleak in the summer of 1976 as
they have appeared subsequently, there was considerable concern
during the missions about the proper interpretation of the
reactions being witnessed. During August 1976, the Viking
scientists believed that the GCMS was one possible tool for
deciding if the reactions observed in the biology instrument were
biological or chemical in origin.
-
- As one observer noted, the gas
chromatograph-mass spectrometer was the court of appeals in the
event that the biological experiments did not present a clear
verdict. 65 With the initial uncertainties from the biology
experiments, the molecular analysis team decided to gamble that
the GCMS had received its sample on sol 8 (see pages 398-400) and
made the first analysis on 6 August (sol 17). Klaus Biemann
reported to the press on the molecular analysis-"the first half of
the first sample experiment of the organic analysis"-the following
day. The soil sample was there! And the oven had worked as
planned. There was always speculation among the news
representatives about what new hardware problems might appear, but
this time the scientists could report, "It did work as predicted,
heated to 200° and stayed there for thirty seconds. The
entire gas chromatograph mass spectrometer worked well like all
gas chromatograph mass spectrometers do." Although the molecular
analysis team was obviously pleased that its instrument was
working well, the results from the GCMS would be the source of the
most frustrating data for those exobiologists who were hoping to
find life on the Red Planet.
-
- About 300 mass spectra, electronically
provided graphs identifying the molecules detected in the Martian
soil sample, were returned by the first run of the GCMS. The
molecular analysis specialists were particularly interested in
determining if carbon compounds were in the sample, since
biochemistry is largely the chemistry of carbon. The basic
structure of the carbon atom enables it to form large and complex
molecules that are very stable at ordinary temperatures. While no
carbon compounds were detected in the first sample analysis, there
was no great concern, since it was believed that the sample would
have to be heated to 500°C before the organics would be
broken down and detected by the instrument. The only surprising
aspect of the first data was the very small amount of water
released by the sample. 66
-
- On 12 August, the GCMS experiment was run
again with the first sample being heated to a maximum temperature
of 500°C. Biemann reported that this analysis "to our
surprise, evolved a large amount of water. Indeed so much that it
gives us trouble in analyzing the data." Still, the critical point
of this analysis was that there were probably no organics. If the
reactions observed in the biology instrument were the consequence
of life, then it was expected that the GCMS would detect organic
compounds [408] in the same
soil. Neither this analysis nor the subsequent one at the
Viking 1 site, nor those carried out at the Viking 2 landing
area, produced traces of organic compounds at the detection limits
(a few parts per billion) of the GCMS. 67
-
- Failure of the gas chromatograph-mass
spectrometer to detect organic compounds was devastating for those
who believed that life on Mars was possible. For Jerry Soffen, the
GCMS results were "a real wipe out." Once he assimilated the fact
that the GCMS had found no organic materials, he walked away from
where the data were being analyzed saying to himself, "That's the
ball game. No organics on Mars, no life on Mars, "But Soffen
confessed that it took him some time to believe the results were
conclusive. At first, he argued with Tom Young that there must
have been no sample present in the GCMS, because there had to be
organics of some sort on the planet. Soffen bet Young a dollar
that the second analysis would prove that the instrument had been
empty. To his dismay, the data indicated instead that there was a
sample in the instrument and that the sample was devoid of
organics.
-
- Klaus Biemann, the molecular analysis team
leader, had some reflections on the search for organic compounds.
Looking in the soil for compounds made of carbon, hydrogen,
nitrogen, and oxygen at the level of a few parts per billion, they
found none. The gas chromatograph-mass spectrometer could have
detected smaller concentrations of organic materials than are
present in typical antarctic soil, which is low in organic
compounds because there is little vegetation and animal life on
that part of Earth. Compared to Antarctica, Mars is devoid of
organic material, and a number of conclusions could be drawn from
that finding. First, no synthesis of organic compounds is
occurring on the surface, at least where the two Vikings landed.
Second, if millions of years ago organic compounds did exist, they
must have since been destroyed. Third, since organic compounds
must be arriving on Mars in the form of meteorites, that material
must have been imbedded in the surface very deeply or, more
likely, destroyed by the planet's harsh environment. Finally, says
Biemann, "if we use terrestrial analogies, we always find that a
large amount of organic material accompanies living things-a
hundred times, thousand times, 10 thousand times more organic
materials than the cells themselves represent." Since the Viking
instruments did not detect any large amounts of organic waste
material, it is difficult to see how microorganisms could be
living at the areas investigated "if they behave as terrestrial
organisms do."
-
- Of course, reminded Biemann, "this does
not rule out a different kind of living mechanism that would
protect its organic constituents very well and, therefore, avoid
this waste of a scarce commodity." Martian organisms could have
evolved along those lines, and as the environment became harsher
and harsher they could have become more and more efficient in
using the organic materials they needed. Viking looked at only two
samples at each of the two landing sites from depths of 5 to 10
centimeters. If organic materials were produced millions or
hundreds of millions of years ago, they
[409] could be present
at greater depths and protected there from the damaging
ultraviolet radiation. The Viking spacecraft could be sitting on
an area containing a deposit of organic material a few meters
down. There could also be other areas on the planet where the
surface material is more protected or where organic material is
now being synthesized and not destroyed. To help answer these
puzzling questions, Biemann and his colleagues had plans to study
in their laboratories the rate of decomposition of certain typical
organics under Martianlike conditions, to determine how fast
organic materials might be destroyed at the surface.
68
-
-
- LIFE OR NO LIFE?
-
-
-
- Soffen's disappointment was shared by
others on the biology team. For years, they had discussed the
scientific possibilities of discovering life or the prerequisites
for life on the Red Planet, and Soffen recalled the long debates
with his colleagues on the subject. Some, like Wolf Vishniac, had
argued that a negative result-that is, no life-was as important
scientifically as the discovery of life. But such a discovery had
not proved very exciting. Before the Viking landings, Soffen had
been very careful in all his public statements to say that they
would likely find nothing on the planet, but personally he had
wanted to find life.
-
- While Soffen believed that it was possible
for life to have developed on Mars, he also thought it likely that
the biology instrument, for a host of reasons, had not been
designed properly to detect it. However, he was also very
confident that if organic compounds had been present, the GCMS
would have detected them. For that reason, he had fought for the
instrument throughout the evolution of the Viking project. Soffen
could have accepted a negative biology result, if there had been a
positive measurement of organic compounds. But positive biology
results could not be interpreted as indicating the existence of
life in the absence of organics. Others have argued that perhaps
Viking landed at the wrong places on the planet. Nearer the poles
where there was a higher moisture content in the soil and
atmosphere, life might exist. Or perhaps, as suggested by Carl
Sagan and Joshua Lederberg, there are Martian microenvironments
where in small oasislike areas life has evolved and survived.
Soffen thought this unlikely since the homogenizing effects of
wind and dust storms would have likely distributed any organic
material all over the planet. He reluctantly concluded that life
on Mars was unlikely. 69
-
- The apparent absence of life on the Red
Planet had a far-reaching philosophical and emotional impact on
members of the biology team. The team had never been a cohesive
group of investigators, and the results of the biology and GCMS
experiments served to accentuate their differences. Norman
Horowitz came to the opinion that there is no life elsewhere in
the solar system. While he did not rule out the possibility in
theoretical terms, he believes, practically speaking. that
scientists will never be able to prove the existence of life on
another planet. Horowitz noted:
-
- [410] There are
doubtless some who, unwilling to accept the notion of a lifeless
Mars, will maintain that the interpretation I have given is
unproved. They are right. It is impossible to prove that any of
the reactions detected by the Viking instruments were not
biological in origin. It is equally impossible to prove from any
result of the Viking instruments that the rocks seen at the
landing sites are not living organisms that happen to look like
rocks. . . . .The field is open to every fantasy. Centuries of
human experience warn us, however, that such an approach is not
the way to discover the truth. 70
-
- One man who is still not convinced is Gil
Levin. He cannot rule out the biological interpretation of the
Viking biology experiment results. "The accretion of evidence has
been more compatible with biology than with chemistry. Each new
test result has made it more difficult to come up with a chemical
explanation, but each new result has continued to allow for
biology," Furthermore, Levin believed that all of the life-seeking
tests showed reactions that "if we had them on earth, we would
unhesitatingly have described as biological." 71 But other members of the biology team were not as
easily convinced.
-
- Vance Oyama, who fathered the gas-exchange
experiment, publicly stated in early 1977 that "there was no need
to invoke biological processes" to explain the results obtained
from the experiments. While far from being accepted by all his
colleagues, Oyama's opinion is one more example of the extent to
which differing explanations can be made to account for the
puzzling data acquired by the biology experiments. Should Oyama's
explanation turn out to be valid, it would affect more than the
biology experiments. It would also help explain the nature of the
magnetic particles that adhered to the magnets on the sampler
head, the interactions between the atmosphere and the surface, and
the early evolution of the planet. His theory begins with a simple
photochemical effect in the atmosphere: the intense solar
ultraviolet radiation breaks down atmospheric carbon dioxide
(CO2) into activated carbon monoxide (CO) and single
atoms of oxygen (O). As the ultraviolet radiation continues to
bombard the atmosphere, some of the carbon monoxide is further
reduced to its constituents, carbon and oxygen. Some of this
single-atom carbon combines with carbon monoxide to produce
carbene (C2O). The carbene in turn combines with carbon
monoxide to form the first key element in Oyama's theory, carbon
suboxide (C3O2). Oyama postulated that the carbon suboxide
molecules were united to form a carbon suboxide polymer.
Intriguingly, the resulting polymer has a reddish cast.
-
- Oyama's theory is consistent with data
from the three biology experiments. Looking first at the
pyrolytic-release experiment, Oyama noted that the carbon-14
isotope was an important factor in explaining the results observed
from this instrument. The decay of the carbon- 14 isotope into
nitrogen- 14 released a beta particle. The resulting energy was
more than sufficient to fracture carbon-carbon, carbon-hydrogen,
and carbon-oxygen [411] bonds. The
breakdown would activate the red carbon suboxide polymer, allowing
it to incorporate the available carbon monoxide. Heating that same
polymer to about 625°C during pyrolysis would produce about
four percent of the original carbon suboxide, with a carbon- 14
label. This single carbon suboxide molecule (monomer) would tend
to stick to the pyrolytic release experiment's organic vapor trap
and with subsequent heating would be released as the critical
"second peak" the specialists observed in the experiment's data.
Taking this another step, Oyama reported that the presence of
water vapor when the sample was exposed to the labeled atmosphere
would lower the second peak. 72
-
- In Oyama's laboratory gas-exchange tests,
the prominent release of oxygen was also less the second time. But
as Oyama said, the reason was very different. In the Martian
atmosphere, the same photochemical breakdown (photodissociation)
that led to the formation of carbon suboxide also led to the
creation of activated oxygen atoms, albeit by a different route.
When these oxygen atoms struck alkaline earths (for example,
oxides of magnesium or calcium), they united to form superoxides
that would release oxygen upon exposure to water vapor. Oyama
argued that less oxygen was released at the Utopia site than at
the Chryse site because the greater amount of water vapor in the
more northerly landing site had previously freed some of the
oxygen in the superoxides near the surface.
-
- In describing the reasons for the results
observed in the labeled-release experiment, Oyama presented the
following scenario. Hydrogen peroxide formed photochemically in
the atmosphere reacted with a catalyst on the soil-grain surfaces
to release oxygen, which diffused into the grains, reacting with
the alkaline earths and metals to form other superoxides.
Atmospheric water vapor could readily convert the superoxides to
peroxides, which in turn could combine with water in the nutrient
to form hydrogen peroxide, H2O2, which would
oxidize the labeled components of the nutrients to release the
labeled CO2. John Oro of the molecular analysis team also
suggested very early that the results from the gas-exchange tests
and labeled release were due to the presence of peroxidelike
materials in the surface of the planet. To explain the process,
Oyama used the example of chemical reactions in human beings. When
hydrogen peroxide (H2O2), a commonly used
disinfectant is applied to a wound, it bubbles. This, Oyama said,
is caused by the presence of iron in the enzyme catalyst. When the
iron combines catalytically with the hydrogen peroxide, it
releases bubbles of oxygen. Oyama believed that a similar process
is at work on the surface of Mars.
-
- Having searched for possible Martian
catalysts, Oyama concluded that there is one likely candidate-a
form of iron oxide known as gamma Fe2O3, or maghemite. On Earth, this is usually found only
around the edges of hydrothermal or magnetic activity, where the
temperatures range between 300° to 400°C. The abundance
of water on Earth has converted much of the maghemite into a
noncatalytic form, but on Mars this material has
[412] survived
virtually unaltered. Oyama thinks that it probably was produced
either by an episode of volcanic heating or by heating that
accompanied a period of meteoritic impacts. While this probably
occurred early in the planet's history, he believes that it took
place after the large quantities of water others suspect once
existed had disappeared. Otherwise, the maghemite would have been
rendered non-catalytic, just as it has been here on Earth. This
explanation is a complex one, but as Jonathan Eberhart, writing
for Science News , has reported: "Oyama's theory will have to stand
the test of time, additional data and competing theories. But it
does show that looking for life on other worlds has the potential
for making valuable contributions in other fields as well."
73
-
- That there is still disagreement over the
Viking biology results has caused some hard feelings among members
of the biology team. Summarizing the situation after the results
were in, Jerry Soffen said that he would expect the following
responses if Horowitz, Oyama, Levin, and he were asked to
participate in another Mars-bound biology investigation: Horowitz
would not want to participate; Viking had satisfied his curiosity
on the subject. Oyama would probably take part, but he would not
expect to discover life. Gil Levin still believed that life may be
discovered on the Red Planet. He had started with the goal of
proving that there was life on Mars, and for him it was an
engineering problem: How do you prove that there is life on Mars?
To some of his colleagues, this was the attitude of an engineer,
not the professional skepticism of the scientist. Examining his
own position, Soffen said that he had never been certain about the
possible existence of life on Mars, but he had hoped that it might
be found. At no time, however, had he committed himself to proving
that it actually existed. Horowitz, on the other band, had always
had such strong doubts about finding life that on several
occasions members of the team wondered aloud why he had remained
with the group. For Soffen, disappointments aside, he would like
to return to Mars and look beyond the horizon shown in the lander
photos-looking not for life but for whatever was there.
74
-
- Biology team leader Chuck Klein also had
some thoughts on the search for life. "Before we landed on Mars we
had a variety of opinions, ranging from those who expected to see
no life on Mars to those who expected to see a rather
flourishing-maybe not terribly advanced, but at least a
flourishing life on Mars." Judging from all the Viking mission's
findings, there is no visible flourishing life. But Klein
suggested that the scientists must look more carefully at Mars
"and ask whether the sophisticated biology and the chemistry
instruments have given us clues as to whether there might be some
less obvious kind of life on Mars." Klein believed that they could
reject their pre-Viking model of Martian microbial life, "namely
the Oyama model, which says that Mars should have micro-organisms
similar to large numbers of soil bacteria on this planet." At
neither site was there any indication to support that kind of
concept of Martian biology. That means that either there are no
organisms or any existing organisms do not fit that model.
-
- [413] Even though two
of the biology experiments gave indications that could be
interpreted on first inspection as being the result of some simple
organisms being present, the molecular analysis team found no
detectable organic compounds in the soil samples. The absence of
organics made the biology team very suspicious; the
weak-to-moderate signals in the two experiments might not be due
to biological processes at all. "However, the lack of organics, in
and of itself, does not rule out the possibility of organisms but
makes that whole idea much less attractive," said Klein. As was
noted by other Viking scientists, there is evidence that the
surface material of Mars contains chemicals that are highly
oxidizing and could interfere with the biological tests and mimic
them. "Just as a living organism can, let us say, decompose a
steak by eating it and digesting it, the steak can also be
decomposed by being thrown into acid, with roughly the same end
products." The equivalent to the sulfuric acid in the case of the
Viking biology experiments could be an inorganic non-biological
oxidizing material. Since this kind of nonorganic material seems
to be present on Mars, it could be the cause of the confusing
experiment results. "We tried a few tricks on Mars to see if we
could devise some experiments that might definitely rule out the
possibility that the decomposition seen is due to biology. We have
nor been able to do that so far." Although the two landing sites
were more hostile than the biologists had anticipated, Klein
points out that the Viking data do not really say there is no life
on Mars.
-
- We can certainly say that it is not
rampant, but we can't be sure there isn't some scraggly form of
life for which we just haven't found the right nutrients or the
right location or the right incubation temperature or the right
environment within which to show its presence. That's why it's
going to be very difficult for me, at least, to come out and say
that there is no life on Mars. l think that would not be a
scientific conclusion.
-
- Klein, for one, wanted logo back to Mars.
75
-
- The planetary scientists agree that Mars
is a fascinating place, and Soffen believes it is significant that
no one has criticized Viking or the men who brought it about
because life was not found there. Philip Abelson, editor of
Science, stated categorically in February 1965 that "we could
establish for ourselves the reputation of being the greatest
Simple Simons of all time" if NASA pursued the goal of looking for
extraterrestrial life on Mars. 76 His editorial in Science in August
1976 that reported on the initial results of Viking 1 did not
repeat this complaint, however, nor did he make it in either of
the two subsequent issues that dealt with the Mars findings.
77 Some writers complained that the Martian microbes
had not been given a decent chance-after all, the same ultraviolet
radiation that caused the various photochemical reactions
postulated by Oyama could also have destroyed the organic remains
of many if not all of the Martian microbes- but none faulted the
space agency for having made the search. 78
-
- A November 1976 editorial in the
New York Times was typical of the press reaction. Noting that Mars
had gone behind the sun earlier in
[414] November,
interrupting for a time communications between Earth and the
Viking spacecraft, the editorial suggested that the "temporary
halt in the receipt of new data permits a preliminary evaluation
of what has been accomplished since last summer's historic
landing." It appeared that "the whole field of Martian studies has
been revolutionized and provided with an abundance of new data
that will take years to assimilate fully." Findings on Mars would,
in turn, force a reconsideration of the hypotheses concerning the
origins of life on Earth. Referring to the postulated superoxides
in the Martian soil, the Times
noted, "Now the possibility is
being discussed that such a superoxide existed here on Earth in
the primeval years and that it is this weird substance that
provided the oxygen that now makes Earth such a hospitable planet
for human and other familiar life forms. The classic explanation
that the plant life produced most of earth's free oxygen is now
being re-examined." Even the experiments of Miller and Urey in the
early 1950s regarding the synthesis of prebiotic molecules could
be questioned in light of the Viking investigations, "....the data
from Mars have reminded scientists that electric discharges and
accompanying ultra-violet radiation can also break down and
destroy complex organic molecules as well as form them. All of a
sudden the conventional wisdom about the development of life on
Earth seems neither so certain nor so inevitable as it did before
the Viking landings last summer." Although most scientists would
not agree that the results of Viking were sweeping away the
foundations for the studies of the origins of life, they would
agree that "the Viking experiments have already been even more
fruitful than their backers expected." 79 Perhaps the basic reason that there were no serious
complaints about the Viking missions was that Mars had turned out
to be a far more interesting place than anyone had predicted and
more exciting than generations of scientists had expected.
-
-
OTHER RESULTS
-
-
-
- Viking's explorations and discoveries did
not stop with the search for life. The great disappointment felt
by the biologists was tempered to a degree by the wealth of other
findings.
-
-
- Radio Science
-
-
- One group of Viking investigators who did
not have any scientific instruments of their own
*** on the four spacecraft but whose work assisted many
scientists was the radio science team led by William H. Michael of
the Langley Research Center. By analyzing the radio beams sent
from Viking to Earth, specialists could determine precisely where
the landers touched down and certain atmospheric and ionospheric
properties of Mars, as well as gather data about the surface and
internal properties of the planet and
[415] about the solar
system. The team's work can be divided into three general areas,
as shown in table 55.
-
-
-
Table
55: Viking Radio Science
Investigations.
-
-
-
- 1. Dynamical, surface. and internal
properties of Mars
- Spin-axis orientation and motion
- Spin rate
- Gravity field
- Figure
- Surface dielectric constant
-
- 2. Atmospheric and ionospheric properties
of Mars
- Pressure, temperature, and
density-altitude profiles
- Electron-number density-altitude
profiles
-
- 3. Solar system properties
- Ephemerides a of Mars and
Earth
- Masses of Martian satellites
- Interplanetary medium
- Solar corona
- Tests of general relativity
-
-
- a Ephemerides are tabular statements of the predicted
positions of celestial bodies at regular intervals.
-
-
-
-
- Investigations of the locations of the
Viking landers and the dynamical properties of Mars use primarily
radio tracking of the landers, with some reliance on radio
tracking of the orbiters for calibration. Determination of the
gravity field and atmospheric and ionospheric properties use radio
tracking of the orbiters, while the solar system and surface
properties investigations rely on combinations of orbiter and
lander radio tracking data. On Earth, the scientists use the
transmitting, receiving, and data collection facilities of NASA's
Deep Space Network at the 64-and 26-meter stations in California,
Australia, and Spain. 80
-
- Although radio science operations began
during Viking's cruise to Mars when the orbiter high-gain antenna
was activated and tracking data were received, this activity was
mostly related to checkout procedures, with some effort devoted to
data and systems calibration. More immediately useful work began
after the first landing, as doppler and range data became
available for the first time between Earth and a spacecraft on
another planet. From the first few days of tracking, the radio
science specialists were able to ascertain "the location of the
lander, the radius of Mars at the landing site, and the
orientation of the spin axis of Mars." Additional data from both
landers led to an initial determination from Viking findings of
the spin rate of the Red Planet. After analyzing signal amplitude
data from the lander-orbiter relay link, Michael and his
colleagues were even able to suggest that the surface material
around the first lander had electrical properties similar to that
for pumice or tuff, a volcanic rock.
-
- [416] The precision of
future Mars maps will be improved considerably, especially in the
30° south to 60° north latitudes, as a result of the
radio science team's work during the extended mission's
low-altitude gravity survey. As the second orbiter assumed a lower
orbit (about 300 kilometers), the scientists measured the effect
Martian gravity had on orbiter accelerations. They noted that
Olympus Mons produced a very large gravitational acceleration,
while prominent, though smaller, perturbations were observed over
Tharsis Montes and Elysium Planitia. Results from a bistatic radar
experiment will also help specialists identify Martian features
more accurately by shedding light on surface reflectivity, surface
roughness, slopes at various scales, and electrical properties of
the surface in regions not accessible to Earth-based radar. These
surface parameters are derived "from spectral analyses of signals
transmitted toward specific locations on Mars from the orbiter
antennas, reflected from the surface of Mars, and received at the
Earth tracking stations." Besides being useful for mapping and
geological interpretations, these findings will simplify the
identification of future landing sites on Mars.
81
-
- Other questions include confirming the
Einstein theory of relativity by a time-delay test-measuring how
much the spacecraft signals are slowed as they pass near the sun
and how the precession rate of Mar's orbital perihelion varies.
During conjunction, data were gathered for studies of the solar
corona. The team was also interested in more accurately measuring
the distance between Earth and Mars and in determining the masses
of Martian moons Phobos and Deimos. Viking's extended mission
promised to be a busy time for the radio science experimenters, as
did the period immediately following actual data acquisition. It
would take many years to analyze all the results.
-
-
- Physical Properties
-
-
- The physical properties team was to draw
conclusions from a composite of data from other experiments, to
define the physical properties of the Martian soil. Richard W.
Shorthill, team leader, stated that the team had been successful
in describing the characteristics of the soil. But what it
encountered was unlike any soils on Earth.
-
- At the Viking 1 site were
two kinds of surfaces to investigate, the so-called rocky flats
and the sandy flats. The bulk density (the number of grams per
cubic centimeter) in the rocky flats area was slightly higher than
in the sandy flats. At the second landing site, the bulk density
was higher than the sandy area. The team determined the properties
of the Martian soil by examining photographs of the trenches dug
by the surface sampler. Cohesion (how the particles stick to each
other) was ascertained by taking the dimensions of the trenches
and the heights of the side walls and noting the collapsed state
of the walls. The cohesion exhibited in the Martian trenches was
similar to that found on Earth in a trench dug in wet sand.
However, since the Martian soil is so very dry, the cohesion must
have been [417] caused by the
electrical properties of the soil. Adhesion (tendency of the
particles to stick to other objects) was determined by observing
the soil that stuck to the sides of the surface sampler head
before and after it vibrated. "We actually did some laboratory
accelerometer tests on the vibrator at Martin Marietta while we
were still on the surface of Mars to get a calibration of the
adhesive forces," remarked Shorthill. By pushing the surface
sampler into the surface until the force of the action turned on a
micro- switch, the soil's penetration resistance could also be
measured. 82
-
-
- Magnetic Properties
-
-
- The magnetic properties experiment
produced some interesting data, too. This investigation revealed
an abundance of magnetic particles on the Martian surface, in both
the soil and the very fine dust. On Earth, the most common
magnetic particles are either iron metal or iron oxides,
indicating that the red coloration of Martian soil may be caused
by a highly oxidized iron, which is normally nonmagnetic on Earth.
Robert B. Hargraves, leader of this experiment team, noted that
two kinds of iron oxide exist on Earth-magnetite and hematite.
Since hematite is nonmagnetic, perhaps the red mineral on Mars is
magnetite with a coating of red hematite. But Mars is not Earth.
"From what we've seen from the Martian imagery, these magnetic
particles themselves appear red and they appear virtually
indistinguishable from the average surface material on Mars."
Hargraves admits that they have no direct information with which
to resolve the mystery of the magnetic red soil, but the
specialists planned to continue studying supporting data from
other experiments in the hope of determining its properties more
accurately. 83
-
-
- Inorganic Chemistry
-
-
- In the inorganic chemistry investigation,
scientists analyzed the chemical elements in the Martian soil with
an x-ray fluorescence spectrometer. Lander 1 acquired five soil
samples successfully, three collected during the primary mission
and two during the extended mission; the second lander acquired
four samples for a combined total of 620 cubic centimeters of
Martian soil. Each sample was sifted through a funnel to measure
the precise size of the sample and then charged with high-velocity
particles from an x-ray source.
-
- When the spectrometer was supplied with a
sample, the data were sufficient to detect the presence of iron
(12-16%, maximum limits), calcium (2-6%), silicon (15-30%),
titanium (0.1-1%), aluminum (1.5-7%), magnesium (0-8%), sulfur
(2-7%), cesium (0-2%), and potassium (0-2.5%) Lander 2 attempted
to retrieve rock samples three times and failed, because what
appeared to be rocks in lander images were actually small crustal
particles that crumbled when disturbed. The scientists believe
there are pebbles but were unable to analyze one.
84
-
- [418] Benton C. Clark,
deputy team leader of the inorganic analysis team. commented that
the "most striking factor between the two Viking landing sites is
that the soil composition [chemical] is extremely similar in both
cases. This is true for all elements we can detect in the soil
including the very high" sulfur content, almost 100 times greater
than the amount of sulfur found in Earth or lunar soil. One
specialist remarked that they would be hard pressed to find such a
closely matched pair of samples at such widely divergent sites on
Earth, or even on the moon. The chemists think the giant dust
storms that occur approximately every two years probably have
mixed up the soil very efficiently and distributed it all over the
planet as a fairly uniform mixture.
-
- Despite the similarity of the soil from
the two sites, different samples from the same location did
indicate some differences in soil chemistry. ÒIn one case,
we get a higher sulphur content when we pick up a little dirt
clod. In other cases, when we push a rock aside and sample the
surface directly beneath it, we in general get a lower iron
content and a somewhat higher sulphur content." Perhaps the soil
under the rock was an older soil, whereas material out in a free
area may have been the result of more recent dust storms-"recent
in this case meaning the last thousands to millions of years." The
chemists' findings have led them to believe that the Martian soil
may have been derived from rocks with a very high magnesium and
iron content. 85
-
-
X-ray fluorescence spectrometer.
-
-
-
- [419] The Media
-
-
- Public interest may have been diminished
by the failure to detect life, but many science writers continued
to pursue the Viking science results. Almost weekly until the end
of the prime mission in November when Mars disappeared behind the
sun during conjunction, the press carried reports of scientific
news from Mars. As Jerry Soffen told reporters at the second
Viking science forum in August 1976, he and his colleagues were
gratified by "the splendid coverage" they were getting, and he did
not mean just the volume, which was considerable. The scientists
had been impressed by the quality, as well:
-
- All of us really want to thank you and
tell you how grateful we are for the remarkable clarity that has
emerged as a result of this very open style that we are developing
right now... We have tried to each time answer your questions as
clearly as we could and I know how difficult it is, as a reporter,
to try to cover and clarify issues that seem to emerge one day and
sometimes....appear to be contradictory on the next day.
86
-
- One example of the coverage given Viking
is a series of articles in Science
News by Jonathan Eberhart, the
journal's correspondent in residence at the Jet Propulsion
Laboratory during the primary mission. Respected by all his
colleagues, Eberhart had a way of making understandable the
complexities of science on Mars. Eberhart reported, among other
accounts, efforts to move one of the rocks with the second
lander's sampler arm, to find soil that had not been exposed in
recent time to harsh ultraviolet radiation. As with all other
maneuvers of the arm, the preparations took more than three weeks
of consultations with more than a dozen specialists. The first
attempt was a failure. The rock, blocking the first
sample-acquisition site, refused to budge. Some persons thought
that the rock might be frozen in place, but Priestley Toulmin of
the inorganic analysis team argued that it was probably just the
"tip-of-the-iceberg"; more of the rock was likely hidden below the
surface. "Mr. Badger," **** the second candidate for displacement, was
successfully moved. As the Viking lander team continued its
investigations of the immediate region around the landers-pushing
rocks, digging trenches, taking pictures, and measuring their
findings-the science writers continued to report on the events.
87
-
- All the Viking mission activities prompted
Gerald Soffen to comment in his Dryden lecture at the American
Institute of Aeronautics and Astronautics' 16th Aerospace Science
Meeting in Huntsville, Alabama, in January 1978, "How remarkable!
We are performing chemical and biological experiments as though in
our own laboratories. Taking pictures at will, listening for
seismic shocks and making measurements of the atmosphere
[420] and surface. All
of this from the first spacecraft ever to be landed successfully
on Mars." 88
-
-
- Management
-
-
- At the end of the primary mission in
November 1976, some major changes took place within the management
structure of the Viking Project Office. Several persons who had
led Viking since its inception moved onto new positions. Jim
Martin left NASA to become vice president of advanced programs and
planning at Martin Marietta Aerospace in Bethesda, Maryland.
89 Tom Young, who had been serving both as Viking
mission director and as Martin's deputy for JPL operations, took
the post of director of lunar and planetary programs at NASA
Headquarters. 90 For a time, Soffen maintained his position as
Viking project scientist, but he was often called on to be a
roving ambassador for the Mars project, traveling around the world
telling scientific and lay audiences about the "real Mars" they
had discovered. When Viking entered the extended mission phase in
mid-December 1976, following the end of solar conjunction,
however, many familiar faces still remained to complete the
project. G. Calvin Broome had become project manager and mission
director, and Conway Snyder, formerly orbiter scientist, first
acted and then assumed full authority as project scientist.
91
-
- With the start of the extended mission,
one phase of Mars exploration had come to an end. The goal of
landing and successfully operating an unmanned scientific
laboratory on the surface had been achieved, and vast archives of
new and exciting information about the Red Planet had been
amassed. The extended mission properly belongs to the post-Viking
era, a period of evaluation and appraisal, With this initial
scientific reconnaissance over, the issue facing the National
Aeronautics and Space Administration was, What next? Viking,
scientists hoped, was only a first step. The debate over
subsequent steps would require decisions about not just exploring
Mars but also how exploring Mars fitted into the overall scheme of
NASA's planetary programs. One chapter closed, it was time to
begin a new one.
-
-
* Sol is used
to designate the Martian day, which is 39.6 minutes longer than an
Earth day; 20 July was listed as sol O because a few hours were
left in the sol (local lander time) at the time of landing. Sol 1
began late on 20 July, at the first lander 1 midnight.
-
- ** The relay
links for the first 11 sols were pre-programmed for redundant
playback and transmission to Earth of the lander-recorded data so
as to prevent loss of any important information.
*** An X-band
downlink on the orbiters was added specifically to enhance radio
science capabilities and to conduct communications
experiments.
-
- **** Henry J.
Moore II named four large Martian rocks after characters - Mr.
Badger, Mr. Mole, Mr. Rat, and Mr. Toad - from Wind in the Willows
by Kenneth Grahame.
-
-
-