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MPC Theatre: Comet Chasers
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1995-05-24
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In the early days of the solar system, there were vast amounts of comets and asteroids
flying around, violently smashing into the young planetary bodies. Much of the evidence
for this ancient activity is to be found on moons of the planets, where comet and asteroid
impacts are not eroded by dynamic conditions on larger worlds.
Moons, or natural satellites, have been found in a wide variety of shapes and sizes, ranging
from Saturn's large moon Titan, which has its own thick atmosphere, to the Martian moon
Deimos, which is nothing more than a captured asteroid. Other moons, such as Miranda
in the Uranus system, show signs of massive collisions that reshaped the entire body.
The planet Earth is unique among the terrestrial worlds, in that it has a large spherical
satellite. Luna, or "the Moon," shows signs of heavy bombardment in the early days of the
solar system. Mars is the only other terrestrial world with natural satellites, Phobos and
Deimos, which appear to be asteroids captured from the nearby asteroid belt.
The outer gas giant planets, by contrast, have large diverse systems of satellites that
resemble small solar systems. Jupiter has four particularly large moons called the Galilean
satellites, including the largest satellite in the solar system, Ganymede. Saturn has only
one very large moon, Titan, which has a thick atmosphere of organic compounds. Saturn,
however, with at least 22 moons, has the largest system of satellites of all the planets.
The most interesting satellite of Uranus is Miranda, a small world with a bizarre jumbled
appearance. It appears that Miranda was broken up by a severe collision with another
body, and then reassembled with the pieces turned inside-out. Triton, the largest moon of
Neptune, appears to have a very thin atmosphere of nitrogen and methane, and is the
coldest place ever explored in the solar system.
Once of the keys to understanding the minor bodies in the solar system is to explore the
moons of the planets. Most natural satellites have preserved their ancient histories on
their static surfaces. The vast differences between the minor bodies in the solar system tell
stories of the ancient past, and help prepare us for the future.