Intro
Asteroids, comets and meteors are left over pieces of rock and other
matter that didn't get made into planets or moons at the beginning of the universe. They
are just minor pieces of rock, floating out in space, sometimes in our solar system,
sometimes not. Still, they are interesting to watch or find.
Asteroids
Asteroids are small bodies of rock that orbit the sun. They
are sometimes called minor planets. Most of them orbit the sun between Mars and Jupiter at
the asteroid belt. There are many asteroids crowded in the asteroid belt so eventually
collisions occur. The asteroids are bumped out of orbit and go flying through space.
Asteroids are different from comets in that asteroids do not have a coma or a tail.
Comets
Comets are packages of rock and ice that orbits the sun a little faster
than the planets. Some comets have long orbits that go deep into space then around the
sun. The Halley comet makes tighter orbits around the sun that takes only 76 years to make
a cycle. Comets are mainly thought of by most astronomers to live in a region known as the
Oort Cloud, where there are many comets just floating around. The Oort Cloud is like
a shell surrounding the Sun and extends to a distance about 2 light years from the Sun.
Comets are usually discovered by people with access to some very big telescopes. Famous
comet-hunters include David Levy, Bill Bradfield, and Carolyn and Eugene Shoemaker.
A comet's nucleus (the piece of rock in the middle) contains
frozen gases and dust. The outside layer is a thin crust of dusty material. Then beneath
the crust is ice, gases and dust. When the comet gets inside the orbit of Jupiter it
starts to heat up because the sun is closer. The frozen gases start to turn into gases
instantly and form jets. The escaping gas, or jets, around the comet start to glow or
fluoresce, because of the sun's ultraviolet rays, and causes a coma, or a glow around the
nucleus. The solar wind out in space then pulls the gases back into a tail, the
ion/plasma tail. These tails always point directly away from the sun, and can be a few
kilometers long. The ion/plasma tails are usually colored blue because of the sun
reflecting off them. Comets also have a dust tail that is yellowish in color and come from
the gas jets pulling off dust particles from the nucleus. The larger chunks that fly off
and fall into our atmosphere produce meteor showers.
Meteors
Meteors are only the streak of light in the sky that you see or what we
call shooting stars. A meteoroid is the actual rock that is falling through our atmosphere
to cause a meteor. When meteoroid it enters our atmosphere and it is pulled faster and
faster by our gravity, when it gets to very high velocities the friction from the air
causes it to burn and that causes the flash of light. Then there are meteorites.
Meteorites are usually the pieces of solid rock that have made it through all of our
atmosphere and have succeeded in hitting the ground.
Meteors are quite common. They can come in annual meteor showers which
are pretty exciting. A good time to observe a meteor shower is late October, after
midnight. This kind of meteor shower called the Orionid meteor shower and is caused by the
Halley comet shedding particles into our atmosphere.
This is asteroids is asteroid 951called the Gaspra. The Galileo spacecraft
took this picture of the asteroid when it approached it on Oct. 29, 1991. It is a false
colored image, colored with color data the Galileo sent with the high resolution black and
white image.
The ESA (European Space Agency) mission Giotto took this picture of the
Comet P/Halley with a multicolored camera. From the Giotto mission scientists found that
P/Halley's outer skin is very dark so that means when it enters the inner solar system it
heats up easily.
This is the Comet P/Halley seen from the Earth on March 8, 1986, taken by W.
Liller on Easter Island.
The comet Kohoutek was a long orbit comet that swung around our part of the
solar system in 1973-4. It's not expected back for another 30,000 years. This was taken on
Dec. 21, 1973 from the skylab.
