Asteroids
- 1. Asteroids
- 2. DefinitionAsteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System.
- 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.
- 4. They are smaller than planets but larger than meteoroids.
- 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.
- 6. The distinction between asteroids and comets is made on visual appearance: Comets show a perceptible coma while asteroids do not.Brief HistoryThe first asteroid was discovered in 1801 by Giuseppe Piazzi of Italy.
- 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.
- 11. Currently, asteroids are also referred to by the International Astronomical Union (the only official body that can name astronomical objects) as minor planets.SizeAsteroids vary greatly in size.
- 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.
- 14. One of the smallest, discovered in 1991 and named 1991 BA, is only about 20 feet (6 meters) across.SizeAsteroids range in size from dust particles to many miles across.
- 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.
- 18. However, that theory is no longer held in much regard, for if all of the asteroids in the belt were combined, they would form a body less than 1500 km (932 miles) in diameter -- less than half the size of Earth's moon, and so there is not enough material to make a planet.CompositionAstronomers classify asteroids into two broad groups based on their composition
- 19. FIRST GROUP - dominates the outer part of the belt. - rich in carbon - composition has not changed much since the solar system formed. SECOND GROUP -located in the inner part of the belt -rich in minerals - formed from melted materials.
- 20. CompositionAsteroids are made of rock and metal.
- 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.
- 24. Asteroids have a confusing system of nomenclature, especially when they are on Earth. While still in orbit, they are asteroids. Once they enter the atmosphere, they are called meteors, and once they land, they are termed meteorites.NomenclatureAsteroids have a confusing system of nomenclature, especially when they are on Earth.
- 25. While still in orbit, they are ASTEROIDS.
- 26. Once they enter the atmosphere, they are called METEORS, and once they land, they are termed METEORITES.OrbitsMost asteroids follow elliptical (oval-shaped) orbits in the asteroid belt.
- 27. Groups of asteroids that follow the same orbit are called Hirayama families, named after Kiyotsugu Hirayama, the Japanese astronomer who first discovered them.
- 28. Many asteroids follow orbits outside the belt.
- 29. For example, a number of asteroids called Trojans follow the same orbit as does Jupiter. Three groups of asteroids -- Atens, Amors, and Apollos -- orbit in the inner solar system and are known as near-Earth asteroids. Some near-Earth asteroids cross the path of Mars, while others cross Earth's orbit.Interesting Facts and FiguresAsteroids are too small to be spherical in shape.
- 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.
- 34. As previously stated, if all the asteroids in the belt were combined into one, it would form a body less than 1500 km in diameter. Noting the immense size of Ceres, it comprises over 1/3 the total suspected mass of the belt (2.3 x 1021 kg).Interesting Facts and Figures26 known asteroids are larger than 200 km (124 miles).
- 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.
- 36. Over 300,000 asteroids have been found.
- 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.
- 38. When several asteroids are seen in relatively the same place and traveling along similar orbits, they are called orbital families.