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  The total mass of all the asteroids in the asteroid conveyor belt is about 1/35th of that of our moon。 The largest object in the asteroid conveyor belt, Ceres, makes about 1/3 of the total weight of all the asteroids。

   Ceres is the only dwarf planet in the asteroid conveyor belt。 Vesta is the only asteroid that can ever be seen with the naked eye。

   It's magnitude can reach 5。1, about the same as Uranus。 Although people probably saw Vesta and Uranus thousands of years ago, they were not recognised to orbit the Sun until 200 years ago。

  The first asteroid to be conveyor beltcovered was Ceres, on 1 January 1801, by Giuseppe Piazzi accidentally。 At first he thought this was a comet, then later a planet! When it was realised it was too *** all Sir William Herschel (the astronomer who discovered Uranus) made up the word "asteroid" to describe it, using the Latin word aster, meaning star, and the -oid,conveyor belt, meaning rock or planet。

   In other words a star-like planet, because he couldn't see any details due to the *** all size of the object。By 1807 another 3 asteroids were discovered, but no more were found until 1845 when a persistent asteroid hunter named Karl Ludwig Hencke found a fifth, and sixth asteroid in 1847。

   Ever since then at least one new asteroid has been found each year。In 1891, the first pictures of the night sky were taken to find more asteroids。

   This led to the discovery of many more asteroids。 A picture of the same part of the sky is taken on two different nights。

   When the two pictures are lined up, the stars will be in the same places but an asteroid will have moved。In our modern times,conveyor belt the brightest asteroid, over 280,000 asteroids have been conveyor beltcovered。

   Many more are being found all the time。 Some of these asteroids pass near the earth and astronomers want to find any that come close to our planet。

   Large numbers of asteroids are now being conveyor beltcovered by machines。Three out of four asteroids are made of rock that is rich in carbon。

   The rest are made of the metals iron and nickel。 About half of these are pure iron and nickel; the rest are mixed with compounds of silica, the element that makes up rocks。

   Each of the larger metal asteroids conveyor belttains huge amounts of iron: much more than is mined every year on Earth。

   Vesta, the brightest asteroid,conveyor belt so Ceres is 1, has a very unusual composition - being made of high-density volcanic rocks。

  Scientists are very interested in what asteroids are made of because it can help them learn how the solar system was formed。

   Several spacecraft have visited asteroids to learn more about them。