Solar System Exploration
In October 1994, Swiss astronomers Michel Mayor and Didier Queloz reported their discovery of a large planet (about half the mass of Jupiter) orbiting the star 51 Pegasi. American astronomers Geoffrey Marcy and Paul Butler of San Francisco State University verified the discovery. The only previous evidence of planets orbiting another star was the unexpected discovery of at least two planets in orbit around a pulsar, the remnant of a supernova. 51 Pegasi is a normal star, somewhat older than our Sun, but the new planet is dramatically different from anything found in our own solar system. Despite its massive size, this planet orbits so close (about 5 million miles) that it is within the hot, tenuous outer atmosphere (the corona) of its star and completes a revolution in about 4 days. By contrast, Jupiter orbits the Sun at a distance of nearly 500 million miles and completes a revolution in about 12 years.
Scientists recently gained a new understanding of the asteroid impact that occurred 65 million years ago in modern-day Yucatan, Mexico, that led to the extinction of the dinosaurs. Scientists had thought that the global dust cloud raised by the impact blotted out enough sunlight to disrupt photosynthesis in plants for 3 to 6 months. It was not clear that this was enough time to cause mass extinctions. A new study, by Kevin Pope of Geo Eco Arc Research, Inc., and colleagues at NASA's JPL and the Institute for Dynamics of Geospheres, Russian Academy of Science, revealed that the region where the asteroid struck has thick geological deposits of sulfur-containing minerals. The asteroid impact could have vaporized these mineral deposits and released an enormous quantity of sulfur, which rapidly became transformed into thick clouds of sulfuric acid. These clouds might have extended the photosynthesis blackout period slightly, but more importantly it led to an "impact winter" of freezing or near-freezing temperatures that lasted until the acid gradually rained out of the atmosphere in about 10 years. Land species that survived this long winter might have lived near seacoastsin climatic "refuges" with temperatures moderated by the enormous heat capacity of the oceans.
Training its new and improved optics on objects in our solar system, HST discovered a distant swarm of comets called the Kuiper Belt that was long thought to exist in the outer reaches of the solar system. HST obtained images of the newly discovered Comet Hale-Bopp, showing that the solid part of this comet is much larger than Halley's Comet, giving rise to predictions that Hale-Bopp may be the "comet of the century," when it passes closest to Earth in early 1997.
HST images and spectra also revealed unexpected weather changes on Neptune, Mars, and Venus. There are unexpectedly rapid cloud changes on Neptune. The atmosphere of Mars is much clearer and colder than 20 years ago. Venus has less sulfur dioxide, implying less volcanic activity, than in the 1970s.
Studies of presolar silicon carbide and aluminum oxide grains found in primitive meteorites have led to definitive new insights into the evolution of stars. These grains were formed of material ejected from stars born millions or billions of years before the Sun. They were gently incorporated into asteroid-sized bodies during the birth of the solar system and preserved unchanged until the present time. Scientists used the chemical and isotopic compositions of these presolar grains to infer physical properties of the stars, such as temperatures, atmospheric densities, and the degree of mixing between inner and outer layers. The preservation of the grains has also shed new light on the physical conditions in the primitive solar nebula. The gas and dust in the nebula are known to have been much cooler, on average, and much less homogeneous; otherwise, the presolar grains would not have survived.
New theoretical studies by a scientist at the Lunar and Planetary Institute in Houston have suggested that Pluto's highly eccentric and inclined orbit is a natural consequence of the formation and early evolution of the solar system, rather than the result of a violent event. Pluto likely began in nearly circular orbit with low inclination, but interactions between giant planets and residual planetesimals during the late stages of planet formation caused Pluto to be captured in orbital resonance with Neptune. The resulting gravitational perturbations by Neptune distorted Pluto's orbit. A further consequence of these results is that most of the remaining planetesimals beyond Neptune, the so-called Kuiper Belt Objects, are trapped in narrow zones at the locations of orbital resonances with Neptune. These objects are probably the source of short-period comets that penetrate into the inner solar system.
Scientists from USGS, a bureau within DoI, assisted with final preparations for NASA's Galileo mission, which reached Jupiter on December 7, 1995. USGS staff developed the software system that will be used to analyze Near-Infrared Mapping Spectrometer (NIMS) data. In August 1995, Galileo plowed through the most intense interplanetary dust storm ever measured, and scientists hope to identify the source of this dust phenomenon after further analysis of data.
To support mission planning and data analysis for NASA's upcoming Mars Global Surveyor mission, which is to orbit the planet for one Martian year, USGS completed a revised 1:5,000,000-scale Mars map series of 30 quadrangles and a series of global digital color image models of Mars. On the upcoming Mars Pathfinder mission to explore the Martian surface, USGS specialists in planetary photogrammetry made several large digital image mosaics and extracted digital terrain models of the Mars landing site for use in validating the primary site in Chryse Planitia. On the future Cassini mission to Saturn, USGS made major contributions to planning the observational sequences and helped define software requirements for the uplink and downlink mission operations phase.
The approach of asteroid 1991 JX to 0.034 astronomical units from Earth (its closest position for at least the next two centuries) on June 9, 1995, provided an excellent opportunity for a variety of NASA-sponsored radar investigations. These included the first intercontinental radar astronomy observations, with transmission from the Goldstone Deep Space Net 70-meter antenna in California to reception in Ukraine and Japan. The 1991 JX asteroid is no more than 0.6 kilometers large, making it the smallest solar system object imaged thus far.
Curator: Lillian Gipson|
Last Updated: September 5, 1996
For more information contact Steve Garber, NASA History Office,