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 – 587Â½ miles across and 0.0002% of the earth’s mass.
- 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 6Â¼ 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)
- 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.
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