On June 30, 1908, a small asteroid 330 feet (100 meters) in diameter exploded over the remote region of Tunguska in Siberia, destroying more than half a million acres of forest. On March 23, 1989, an asteroid 0.25 miles in diameter came within 400,000 miles of Earth; if that asteroid had come 6 hours later, Earth would have collided with it. Imagine the devastation it might have caused…
The Asteroid Belt
Actually, asteroids are pretty interesting objects [when they aren't colliding with Earth]. Asteroids are made of rock and/or metal, but are too small to be considered as planets or moons (in cases where they may orbit a planet).
When would you think the first asteroid was discovered? Probably a few hundred years ago, huh? Well, the first asteroid to be discovered was on January 1, 1801 [new century, new discovery] by Giuseppe Piazzi. Piazzi named it Ceres, after the Sicilian goddess of grain.
Ceres is the biggest of all known asteroids. It has a diameter of 933 km (579.5 mi) and 25 percent of the total mass of all known asteroids. Ceres is so big compared to other asteroids that it actually is almost twice the size of the next biggest known asteroid (Vesta), which 525 km (326 mi) in diameter.
Asteroids are not very dense. In fact, most of the asteroid that has been studied (we have only had a chance to study a few asteroids that are in space), Mathilde, shows a density only a little bit higher that water meaning that it isn't a solid body, like a planet or moon, but instead a compressed collection of debris.
The main body of asteroids is orbiting the sun between Mars and Jupiter. There are also a few Near-Earth asteroids (NEAs) that are closer to Earth.
The Kuiper Belt and Planet X
Rather than ending abruptly at the orbit of Pluto, the outer solar system contains an extended belt of small bodies. These bodies are classified as part of the Kuiper Belt, found by astronomer Gerard P. Kuiper. So far, around 35 of these objects have been discovered.
The main difficulty with identifying these objects is that they are extremely far from the sun and receive very little sunlight. On top of that, they are usually cold and dark and do reflect very little of the light back. So far, none of these are large enough to become planets, but scientists are still searching for the possible Planet X, the possible tenth planet.
