3. Asteroids are material left over from the formation of the solar system. One theory suggests that they are the remains of a planet that was destroyed in a massive collision long ago.
5. The term "asteroid" has historically been applied primarily to bodies in the inner Solar System since the outer Solar System was poorly known when it came into common usage.
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7. He named it "Ceres" after the Roman goddess of grain.
8. Ceres is the largest known asteroid at approximately 950 km (590 miles) in diameter, and it lies in the belt of asteroids between Mars and Jupiter at an average distance from the sun of 2.6 A.U.
9. Ever since, asteroids have received an official designation of a number (starting with Ceres of number "1"), and most larger ones have received a name based in Roman mythology.
10. If they have a name, then they are usually referred to with the number then the name, such as 951 Gaspra.
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12. The largest and first known asteroid, Ceres, was discovered in 1801. It is 580 miles (933 kilometers) in diameter.
13. Ceres is believed to contain about 1/3 the total mass of all the asteroids.
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15. Most current theories hold that asteroids are bits and pieces left over from the formation of the solar system.
16. They are also formed from other asteroids as they collide and break apart, as comets disintegrate, or even when the outer moons of the larger planets collide.
17. Past theories have suggested that the asteroids are remnants of a planet that was destroyed early in the solar system's history.
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21. They are mainly grouped into three categories: STONY, IRON-NICKEL, and a MIXTURE OF THE TWO.
22. Most asteroids that we know about (92.8%) fall into the first category, and are made of Silicates. 5.7% are Iron-Nickel.
23. The balance form the third type. Despite their relative abundance, stony asteroids that have fallen to Earth are the hardest to find because they look like terrestrial rocks and they weather much faster than the metallic ones.
27. Groups of asteroids that follow the same orbit are called Hirayama families, named after Kiyotsugu Hirayama, the Japanese astronomer who first discovered them.
30. Instead, they are usually ellipsoids, but some are dumbbell-shaped, and others form even stranger ones.
31. Asteroids bare a tale of the violence of the solar system; the larger ones have many sizeable craters pockmarking their surface.
32. One of the most surprising features of asteroids is that several have been observed to have moons of their own.
33. The first asteroid to be observed with a moon was 243 Ida (58 x 23 km); it's moon is called Dactyl, and measures approximately 0.75 x 0.87 x 1.0 miles. It is now estimated that between 10-30% of asteroids have moons.
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35. We probably know 99% of the asteroids that are greater than 100 km (62 miles), and there are probably literally millions of asteroids that are greater than 1 km (0.62 miles) in diameter.
37. When asteroids break apart, the pieces don't always fly off in random directions. Sometimes, they will continue in the same orbit as the original asteroid.
![Definition ,[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)