Icy world found inside asteroid
By Ron Cowen
New observations of Ceres, the largest known asteroid, suggest that frozen water may account for as much as 25 percent of its interior. If this is true, the volume of ice on Ceres would be greater than that of all the fresh water on Earth.
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The evidence comes from Hubble Space Telescope images showing that the 930-kilometer-wide asteroid is smooth and almost perfectly round. Simulations show that a body as massive as Ceres can have that shape and texture only if materials inside it have separated into layers of higher– and lower-density compounds. A period of heating and cooling, such as that experienced by the solar system’s rocky inner planets, could have caused light material to move toward the asteroid’s surface and denser material to sink.