In some respects it resembles a 'C-type' asteroid, a primitive body left over from the formation of the solar system.
在某些方面,它类似于C型小行星,前身从太阳系形成中遗留下来。
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So Pluto should be a planet, as should Eris and the dwarf planet Ceres (the largest body in the asteroid belt between Mars and Jupiter), as well as many other objects.
As one side of a rotating body (i.e. an asteroid) is heated by the sun's radiation, the surface rotating away from the sun will be warmer than the surface rotating into sunlight.