110 8. EVOLUTION OF THE SOLAR SYSTEM
Figure 8.6: e nucleus of comet Tempel 1. (Image credit: NASA/JPL-Caltech/UMD, Public
Domain.)
8.1.6 METEORS AND METEORITES
Small, solid bits of solar system stuff often collide with Earth’s atmosphere. e intense heat
generated by friction with Earth’s upper atmosphere causes the air along the particle’s trajectory
to glow with a visible trail called a meteor. Since these particles impact the atmosphere at relative
speeds of tens of kilometers per second, and the substantial kinetic energy that comes with that,
even a pea-sized particle can make a bright meteor.
Most meteors have their origin in the short-period comets, their nuclei broken up by close
passages with the Sun. ese relatively insubstantial pieces typically vaporize (or are reduced to
dust) high in the atmosphere.
But larger pieces of rock and metal—mostly broken pieces of asteroids that have collided
with each other—can make it all the way to the ground. ese meteorites can then be studied in
the laboratory; studies of meteorites provide much of the foundation for our knowledge of the
asteroids. See Figure 8.7.
8.1.7 KUIPER BELT OBJECTS (KBOS)
e Kuiper belt is a distant region of small solar system bodies that are mostly a mix of rock and
ice. e Kuiper belt is much closer than the Oort cloud; it begins at about the orbit of Neptune.
Like the asteroid belt, the Kuiper belt is aligned somewhat with the plane of the orbits of the
planets.
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