Asteroid: Difference between revisions

An '''asteroid''' is a [[Outer space|space]] [[Stone|rock]]. It is a small object in the [[Solar System]] that travels around the [[Sun]]. It is like a [[planet]] but smaller. They range from very small (smaller than a [[car]]) to 600 miles (1000 km) across. A few asteroids have [[asteroid moon]].

The name "asteroid" means "like a star" in the ancient [[Greek language]]. Asteroids may look like small stars in the sky, but they really do move around the [[Sun]], while stars only seem to move because the [[Earth]] spins. Like planets, asteroids do not make their own [[light]]. Because of this, some people think "asteroids" is not a good name, and think that the name "planetoid" ("like a planet") would be a better name.

Giuseppe Piazzi found the first asteroid, in 1801. He called it [[1 Ceres|Ceres]], and it is the biggest object in the [[asteroid belt]]. Others, like [[3 Juno|Juno]], [[2 Pallas|Pallas]], and [[4 Vesta|Vesta]] were found later. In the 1850s so many had been found, that they were numbered by a [[Minor planet designation]] starting with [[1 Ceres]]. Today, astronomers using computerized [[telescope]]s find thousands of asteroids every month. [[Asteroid impact prediction]] is one of the purposes.   

Asteroids are the leftover [[rock (geology)|rock]] and other material from the formation of the [[Solar System]]. These rocks were too small to come together to make a planet. Some are made of [[carbon]] or [[metal]]. Depending on what's on the surface, they are classified into various [[asteroid spectral types]] including Type M (metal), Type S (stone), and Type C (carbon).

Most asteroids in our [[Solar System]] are in the [[asteroid belt]] between [[Mars (planet)|Mars]] and [[Jupiter (planet)|Jupiter]]. Many are not in the main asteroid belt. The ones that come close to Earth are called [[Near-Earth asteroid]]s. Many scientists think asteroids striking the Earth killed off [[K/T extinction event|all the dinosaurs]] and caused some of the other [[extinction event]]s.