Learn more about the thousands of miniature planets called asteroids that orbit the sun.
Asteroids are like tiny, rocky planets that orbit the sun. Most asteroids can be found in the space between the orbits of Mars and Jupiter. This area is known as the Asteroid Belt. Asteroids are sometimes referred to as minor planets. The larger asteroids, in particular, can be referred to as dwarf planets. Mars's two moons are believed to be of asteroid origins.
The Largest Asteroids
The largest known asteroid is also, not surprisingly, the first one that was found. It is named Ceres and was first sighted by the Italian astronomer Giuseppe Piazzi on January 1, 1801. The name Ceres comes from the goddess of grain. Ceres is 933 kilometers across, which is similar in size to Pluto's moon, Charon. The asteroids were numbered as they were found, therefore, Ceres is sometimes called 1 Ceres.
The next largest asteroids were also found back in the 1800s. Some of the other large asteroids are 2 Pallas, 3 Juno, 4 Vesta, and 10 Hygiea. There are hundreds of thousands of asteroids in size from about 10 kilometers up to Ceres, but possibly millions that are 1 kilometer and smaller.
Asteroid Composition
Asteroids are divided into three main categories: C-type, S-type, and M-type. The C-type includes the majority of asteroids: these are dark, carbonaceous chondrites composed of materials similar to that of the sun. The S-type includes about 15% of asteroids that contain a metal mix, such as nickel-iron with magnesium. The last category into which most asteroids fall, the M-type, are pure nickel-iron. Both of these last two classifications that contain metal are brighter and easier to spot.
Most asteroids are commonly thought to be loose masses of rock that have bumped into each other during orbit and stuck through a common center of gravity. The pieces are believed to be leftover from the formation of the solar system. Because of this construction, the mass of most asteroids is very low. The largest asteroid, Ceres, is believed to have nearly half the mass of all objects in the Asteroid Belt.
Asteroids and their "Impact" on Earth
Asteroids have, quite literally, had a large impact on Earth. The Barringer Crater in Arizona was made by an impact from a space rock around 50,000 years ago. A wide swath of Siberian forest was flattened by a meteor exploding in Earth's atmosphere in 1908; this is known as the Tunguska Event. A large space rock that hit the Yucatan Peninsula region millions of years ago is thought to have contributed to the demise of the dinosaurs.
Learn more about the threat of asteroids, comets, and meteors from space.
Sources: Nine Planets, NSSDC
