Chapter 7-3

The Sun, the Earth, and "In Between"

illustration of the sling like orbital path necessary to launch a spacecraft into deep space
Getting a boost from Jupiter.
To learn more about the Sun, we need to investigate it from closer range and especially from above its polar regions, the last unexplored zones of the solar atmosphere. Present spacecraft propulsion devices are not adequate to send a craft directly over the solar poles, but it would be possible to launch a spacecraft from Earth out around Jupiter, whose powerful gravity can boost a spacecraft out of the plane of the planets' orbits and into a new trajectory that would send it racing over the Sun (picture below). This figure shows a mission concept involving two spacecraft, which would simultaneously explore the north and south poles of the Sun.

illustration of 2 reasearch spacecrafts entering orbit around the sun

We now know that the Sun touches the Earth not only with heat and light but with magnetic fields and streams of charged atoms that fill what we once thought of as empty space.

In the near future, for both scientific and practical reasons, we need to study both the Sun itself and the dynamic phenomena in space that bind us to it. In the past, we have always had to look at the Sun sideways. The Earth's orbit lies near the plane of the solar equator, and from Earth we see clearly only the Sun's midsection. The higher latitudes are harder to see, and the polar regions of the Sun are extremely difficult to study from the Earth. The spacecraft launched from Earth generally are constrained to remain near the plane of the Earth's orbit, and thus are subject to the same viewing limitations.

Yet it is at the Sun's poles, as we learned from observations in space, that some of the most significant and unexpected solar processes occur. Above the Sun's poles, streams of charged particles pour out into space through the coronal holes. To understand the Sun and its effects on Earth, we need somehow to rise up and look at the Sun from above and below. But we do not have an existing propulsion system capable of carrying a spacecraft over the poles of the Sun.

Nevertheless, a mission is now being planned to send spacecraft over the Sun's poles. The extra thrust needed will come, not from a new kind of thruster, but from the planet Jupiter! In this program to explore the Sun's polar regions, spacecraft would be launched, not toward the Sun, but toward Jupiter. On reaching the giant planet, the spacecraft would cross over its north or south pole and be flung by Jupiter's powerful gravity field back toward the Sun like a pebble whirled from a slingshot. (Similar gravity-assist maneuvers around Jupiter were used with the Pioneer 11, Voyager 1, and Voyager 2 spacecraft to propel them toward Saturn.)

With the extra speed provided by Jupiter, the spacecraft would be aimed to pass over the Sun's north or south pole. A battery of instruments would be used to measure the streams of solar wind particles and to record the magnetic fields associated with the solar-wind. A variety of other measure ments would be carried out as well.

This mission would give us our first indication of what the Sun and its surroundings are like in three dimensions, thus literally adding a new dimension to our understanding of the interactions between the Sun and the Earth.

Understanding all the details of the Sun-Earth interactions is a difficult problem. The volume of space that is involved is huge and filled with complex phenomena: magnetic fields, solar-wind streams, the Earth's magnetosphere, and belts of high-energy radiation. These features change constantly, shifting positions and varying in intensity. To follow and understand these changes, we need to make continuous measurements at widely-separated locations simultaneously. So far, we only have data from a few isolated spacecraft moving on limited orbits. Trying to comprehend the full complexities of the Sun-Earth interaction currently is like trying to reconstruct a motion picture from a few individual frames. Inevitably, there are still great gaps in our understanding.

We now need to make a systematic study of the Sun-Earth region. A mission under study would involve the simultaneous launch and operation of four heavily instrumented spacecraft. One would be located between the Earth and Sun to measure approaching disturbances in the solar wind and the interplanetary magnetic field. Two more would be placed in orbits (one polar, one equatorial) around the Earth to observe the interaction of the solar-originated particles and fields with the Earth's atmosphere and magnetic field. The fourth would be located on the side of the Earth opposite the Sun, to record disturbances that take place in the Earth's magnetic tail downstream from the Sun.

With these spacecraft making simultaneous measurements, we would obtain the data to construct a "movie" of the Sun-Earth interactions. We could detect changes in the Sun's forces and see how the Earth responds to them. We could match the data with information from weather satellites and ground-based weather stations to gauge the effects of the Sun on the weather. This project would be an expedition to explore the space between Earth and Sun, but its discoveries would be used on Earth, hopefully to improve weather prediction, to understand and perhaps prevent communications interference, and to discover the Sun's long-term effects on our climate.

Previous Index Next