Lumps of rock that orbit the Sun


  • they are also known as minor planets.
  • most asteroids are in the asteroids belt – lies between Mars and Jupiter. (diagram)
  • more than one million asteroids bigger than one mile across; more than 200 asteroids are more than 60 miles across.
  • few asteroids come near Earth – these are called Near Earth Objects (NEOs).
  • asteroids were one know as minor planets and new discoveries are recorded by the Minor Planet Centre in Cambridge, Massachusetts, USA – giving each one a unique catalogue number in addition to any name.
  • first asteroids were discovered – Ceres in 1801 by Giuseppi Piazzi.
  • the biggest asteroid Ceres – 587½ miles across and 0.0002% of the earth’s mass.

Asteroids Belt

  • it is located at a distance of 2.1 to 3.3 Astronomical Unit (AU) from the Sun.
  • contains many thousands of objects – some 30,000 have been individually identified.
  • scientists believe that the main belt asteroids are planetesimals left over from the formation of the Solar System – they were prevented from clumping together into a rock planet by the gravity of massive gas planet Jupiter.
  • only one of the main belt asteroids; Vesta – bright enough to be seen with the naked-eye.
  • Ida (photo) – one of the asteroids, photographed by the Galileo Space Probe.; it has an irregular shape (35 x 15 x 13 miles) and is the only asteroid known to have its own natural satellite, Dactyl.
  • a tiny asteroid, Dactyl measures just 6¼ miles in diameter and orbits Ida at a distance of about 60 miles.
  • at the end of the 1990s, the NEAR mission (Near Earth Asteroid Rendezvous) target two other asteroids; Mathilde and Eros; the spacecraft surveyed both asteroids from orbit before landing on the surface of Mathilde in 2001. (diagram)

Trojan Asteroids

  • located at the outer edge of the main belt in two groups that are 60 degrees to both the Sun and Jupiter. (diagram)
  • these groups are believed to be the remnants of larger asteroids that were smashed to pieces by collisions.

Did you know?

  • around every 50 million years, the earth is hit by an asteroids measuring more than 6 miles across.

Back to The Solar System page.

Comments are closed.