ASTEROIDS
Asteroids are
small rocky metallic bodies in orbit around the Sun. Most are in the Asteroid
Belt which orbits the Sun at a distance between Mars and Jupiter. They have
been found from inside Earth's orbit out to beyond Saturn's orbit.
More than 7,000 asteroids have been
discovered. Several hundred more are discovered each year. There are
undoubtedly hundreds of thousands more that are too small to be seen from
Earth.
Some have
orbits that cross Earth's path
and some have even hit the Earth in times past. One of the best preserved
examples of that is the Barringer Meteor Crater near Winslow, Arizona.
he
size of asteroids
Because they are too small to be
considered planets, asteroids are known as minor planets. They range in size
from Ceres, which has a diameter of about 620 miles, down to the size of
pebbles. only 16 asteroids have a diameter greater than 150 miles and only 26
asteroids are known to be larger than 125 miles in diameter.
Biggest. The
largest, by far, is 1 Ceres at 580 miles in diameter. It alone contains about
25 percent of the mass of all asteroids combined.
The next
largest asteroids are 2 Pallas,
4 Vesta and 10 Hygiea which are between 250 and 325 miles in diameter. All
other known asteroids are less than 210 miles across.
What
are asteroids made of?
Asteroids are composed of material left
over from the formation of the Solar System billions of years ago. Asteroids
may be material that never coalesced into a major planet. On the other hand,
they may be the remains of a planet that grew and then was destroyed long ago
in a massive collision with something else. If the estimated total mass of all
asteroids was gathered into a single object, it would be less than 932 miles
across. That's less than half the diameter of our Moon.
