Figure 25.33: This photo captures a meteor - also called a ’shooting star,’ streaking across
the sky to the right of the Milky Way. ( 13 )
all the way through the atmosphere and hits the Earth’s surface. The solid remains of a
meteoroid found on Earth’s surface is called ameteorite.
Meteorites provide clues about our solar system. Many meteorites come from meteoroids
that formed when the solar system formed (Figure25.34). Some are from the insides of
asteroids that have split apart. A few meteorites are made of materials more like the rocks
on Mars. Scientists believe the material in these meteorites was actually knocked off the
surface of Mars by an asteroid impact, and then entered Earth’s atmosphere as a meteor.
Comets
Cometsare small, icy objects that orbit the Sun in very elliptical orbits. Their orbits carry
them from the outer solar system to the inner solar system, close to the Sun. When a comet
gets close to the Sun, the outer layers of ice melt and evaporate. The gas and dust released in
this way forms an atmosphere—called acoma—around the comet. Radiation and particles
streaming from the Sun also push some of this gas and dust into a longtail, which always
points away from the Sun no matter which way the comet is moving. Figure25.35shows
Comet Hale-Bopp, which shone brightly for several months in 1997.
Gases in the coma and tail of a comet glow, and also reflect light from the Sun. Comets
are very hard to see except when they have their comas and tails. For this reason, comets
appear for only a short time when they are near the Sun, then seem to disappear again as