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What Asteroids Are the Smallest, Biggest & Closest to the Earth?

Asteroids are small, rocky objects found within the solar system. They vary in composition; some are solid rock, while others are loosely grouped rubble and still others are made of metal. Their low gravity generally keeps them from forming into spheres, as do the many collisions asteroids encounter. Some asteroids have their own small moons or travel with other similar-sized asteroids.

Where Can Asteroids Be Found?
- Many of the solar system's asteroids -- including all of the largest known asteroids -- can be found orbiting the sun in the asteroid belt, which lies between Mars and Jupiter. The Trojan asteroids are a group of asteroids that share Jupiter's orbit but stay ahead of or behind the planet. Asteroids that orbit the sun inside of Mars' orbit are called near-Earth asteroids.
The Smallest Asteroid
- There is not a particular asteroid known to be the smallest. Using telescopes, astronomers have seen asteroids that are tens of meters across. The current theories on asteroid formation say that they are leftover from the solar system's formation, and that they are also formed from collisions between asteroids, the disintegration of planets or the collision of moons of larger planets. Therefore, there are undoubtedly very small asteroids orbiting the sun that astronomers have yet to observe.
The Biggest Asteroid
- The largest asteroid is approximately 590 miles wide and is called Ceres. It was named after the Roman goddess of grain by Giuseppe Piazzi, who discovered it in 1801. Being the biggest asteroid, Ceres was also the first asteroid to be discovered. Ceres orbits the sun in the asteroid belt and is usually 2.6 astronomical units away from the Earth. Because Ceres is so large, it is (along with other large asteroids) sometimes called a dwarf or minor planet. Ceres takes 4.6 years to orbit around the sun and rotates once every 9.075 hours.
The Asteroid Closest to Earth
- Like the other bodies of the solar system, asteroids vary in their distance from Earth as they orbit the sun. Asteroids are spotted approaching Earth by NASA's Near Earth Object Program several times a year. The closest an asteroid has gotten to Earth without an impact was in 2004, when the 100-foot-wide 2004 FH passed within 26,500 miles (3.4 Earth diameters) above the surface of the planet. 2004 FH was discovered only a few days before it passed by Earth; astronomers predict that objects of similar size come within the same distance of Earth once every two years without being detected.

Astronomy