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Asteroids
General Information
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The first asteroid discovered was found by Giuseppe Piazzi on January 1, 1801. He named it Ceres, after the Sicilian goddess of grain.
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Some asteroids have numbers in their official names, indicating when they were found. “1 Ceres” was the first asteroid found, while “2 Pallas” was second, and so on.
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Several hundreds of thousands of asteroids have been found so far. There are probably hundreds of thousands more than are too small to be see from Earth.
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Most asteroids orbit in the “asteroid belt,” a region between the orbits of Mars (1.5 AU) and Jupiter (5 AU). Near Earth Asteroids (NEAs) are asteroids that closely approach Earth. Other asteroids, called Trojans, orbit with Jupiter: some orbit before the planet, others trail behind.
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Although there are many, many asteroids, the amount of space they occupy is very, very large: the asteroid belt is nothing like what is pictured in movies like Star Wars. The distance between asteroids is very large. Several spacecraft have traveled through the belt to the outer solar system without encountering any asteroids.
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The largest asteroid is 1 Ceres. It is about 580 miles wide, and contains about 25% of the mass of all asteroids combined.
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Although little data exists regarding the density of asteroids, it seems that they’re not very dense. With the help of the spacecraft NEAR (Near Earth Asteroid Rendevous), it seems that the density of the asteroid Mathilde is about that of water: Mathilde is more like a pile of debris than a solid object.
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Pieces thrown off of asteroids by collisions with other objects sometimes make their way to earth. Pieces that are large enough to survive the heat of falling through Earth’s atmosphere to land on the ground are called meteorites.
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One asteroid, Ida, even has its own moon! Ida, shaped somewhat like a potato, is about 33 miles long. Its moon is called Dactyl.
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References
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