Asteroid Facts

  • Asteroids are lumps of rock that orbit the Sun. They are sometimes called the minor planets.
  • Most asteroids are in the Asteroid Belt, which lies between Mars and Jupiter.
  • Some distant asteroids are made of ice and orbit the Sun beyond Neptune.
  • A few asteroids come near the Earth. These are called Near Earth Objects (NEOs).
  • The first asteroid to be discovered was Ceres in 1801. It was detected by Giuseppi Piazzi, one of the Celestial Police whose mission was to find a ‘missing’ planet.
  • Ceres is the biggest asteroid – 940 km across, and 0.0002 percent of the size of the Earth.
  • The Galileo space probe took close-up pictures of the asteroids Ida and Gaspra in 1991 and 1993.
  • There are half a million or so asteroids bigger than 1 km across. More than 200 asteroids are over 100 km across.
  • The Trojan asteroids are groups of asteroids that follow the same orbit as Jupiter. Many are named after warriors in the ancient Greek tales of the Trojan wars.