Amazing Asteroids

 

Asteroid Basics Asteroids are giant chunks of metal and rock. Meteors break from them. There is an entire collection of them just outside of Mars called the Asteroid Belt. What's an Asteroid? At first glance, asteroids (sometimes called "minor planets") are not very attractive. They are just huge hunks of barren rock orbiting the Sun. But someday they may become a source of great riches. The first asteroid ever found was Ceres, discovered by the Italian monk, Giuseppe Piazzi, in 1801. Since then, 4,000 asteroids have been found. The four largest are Ceres, Pallas, Juno, and Vesta. Their diameters range from 154 miles for Juno to 623 miles for Ceres. Most asteroids are found in a great belt between the orbits of Mars and Jupiter, right where there is a big gap between the planets. The asteroid belt orbits the Sun like the rings orbit Saturn. Some scientists once speculated that asteroids were left over when a planet exploded in a collision with another object. But today we think there never was a full-size planet, but rather a few moon-size objects. Jupiter's huge gravity would have prevented them from forming a complete planet. As these mini-planets smashed into one another and shattered, some of the fragments were swept up by planets or got shot out of the solar system by the gravity of the giant planets. Some even hit the Earth (and still do). The fragments that survived are the asteroids. Though most asteroids are in orbits that keep them between Mars and Jupiter, a few get closer. Those that just cross the orbit of Mars are called Amor types. Those that cross Earth's orbit are called Apollo types. From meteorites found on Earth, we know that some asteroids are made mostly of metal. One estimate is that a .6-mile asteroid could have around $1 trillion worth of iron, nickel, cobalt, and platinum. The Apollo asteroids are the easiest ones for spacecraft to reach, because they cross Earth's orbit. Astronauts may one day explore them, and perhaps mine them for minerals.