By Ron Cowen
If planetary scientist Bill McKinnon’s hunch is right, the largest asteroid in the solar system isn’t an asteroid at all. Ceres, as the 470-kilometer-wide object is called, may be a relative of Pluto that formed at the solar system’s fringes but came in from the cold several billion years ago.
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McKinnon, based at WashingtonUniversity in St. Louis, said he was first struck by Ceres’ unusually low density — more similar to icy comets from the outer solar system than the rocky bodies found in the asteroid belt that lies between the orbits of Mars and Jupiter. The density of Ceres, referred to as a dwarf planet, is only slightly higher than that of Pluto. Models suggest Ceres “looks remarkably Pluto-like,” McKinnon says.
But it was a recently developed model of the early solar system that prompted McKinnon to formally propose that Ceres might be an escapee from the Kuiper belt, an outer solar system reservoir of frozen bodies that includes Pluto. He presented his proposal July 15 in Baltimore at the Asteroids, Comets, Meteors conference.