Lesson 30: Classifying Small Bodies
In this lesson, we will learn about the smaller objects in
the solar system, including asteroids, comets, dwarf planets, and meteorites.
Beyond planets and
moons, there are many smaller objects orbiting our Sun,
ranging in size from small particles to dwarf planets like Pluto.
There are several terms used to categorize these objects based on their size and
composition.
The objects too small to be planets, basically leftover planetesimals from
the formation of our solar system, are called asteroids and comets. Asteroids
are the small objects that are rocky in composition, while comets are the ones
that are ice-rich.
Most asteroids lie in the asteroid belt between Mars and Jupiter,
while most comets are
at the outer reaches of our solar system beyond Neptune's orbit -- in the
Kuiper belt and the Oort cloud.
The dwarf planet category was not created until 2006 and is basically an
asteroid or comet that is large enough to be round. As we have discussed
previously, once an object gains a certain amount of size and mass, its gravity
will become strong enough to force it into a spherical shape.
Pluto is the most famous of the dwarf planets since for over seventy years, it
was considered to be one of the nine planets in our solar system. However, the
discovery of Eris, another object roughly the same size as Pluto, along with
other similar large objects out in the Kuiper belt, led scientists to realize
that Pluto is not very unique in its part of the solar system. If Pluto is to
be considered a planet, then there are numerous other large objects out in the
Kuiper belt that would have to be considered planets as well.
When a small object enters our atmosphere,
it causes a flash of light known as a "meteor." The meteor refers to
the flash of light -- not the object itself.
In the rare cases that
the object is big enough to
survive its passage through our atmosphere and reach the surface, it is called
a meteorite.
Most meteorites are pieces of asteroids from the asteroid belt, but occasionally,
they are pieces that were chipped off of the Moon or Mars.