Asteroids are chunks of rock and metal that orbit around the Sun. Scientists think that they are loose material that never formed into planets.
The Main Asteroid Belt is located between Mars and Jupiter.
The total mass of all the asteroids is less than that of the Moon.
There are 26 known asteroids larger than 200 km across. We probably know 99% of the asteroids larger than 100 km across. We’ve cataloged about half of the asteroids in the 10 km to 100 km size range. Scientists still don’t know much about the smaller ones. It’s thought there may be as many as a million 1 km sized asteroids may exist.
The Asteroid Belt
The Asteroid Belt is a region between the inner planets and outer planets where thousands of asteroids are found orbitting around the Sun.
More than 7000 asteroids have been discovered. Several hundred more are discovered each year. There are undoubtedly hundreds of thousands more that are too small to be seen from the Earth.
The Galileo spacecraft photographed Ida and Gaspra on its way to Jupiter. They are the only asteroids which have been studied closely.
Recently, the NEAR mission flew by an asteroid named Mathilde on June 27, 1997, and returned many images. NEAR will be visiting the Eros asteroid in January 1999.
The largest asteroid by far is Ceres. It is 914 km across and contains about 25% of the mass of all the asteroids combined! The next largest are Pallas, Vesta and Hygiea which are between 400 and 525 km across. All other known asteroids are less than 340 km across.
Vesta has been studied recently with the Hubble Space Telescope.
Though they are rarely visible with the naked eye, many asteroids are visible with binoculars or small telescopes.
Asteroid Photos & Movies
Radar images of asteroid Toutatis
Images of asteroid Castalia
Asteroid Vesta photographed by the Hubble Space Telescope
Radar images of asteroid Geographos
Asteroid Gaspra shown in its true color and colorized
Asteroid Ida photographed by the Galileo spacecraft