Ceres is vying with Pluto for title of most mysterious dwarf planet:

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STRANGE NEW WORLD
Glut of papers confirms: we really don’t understand Ceres
The dwarf planet has strange features, and we're struggling to explain them all.
John Timmer - 9/4/2016

On Thursday, Science released a half-dozen papers that analyzed data the Dawn mission sent home from the largest body in the asteroid belt, a dwarf planet called Ceres. Headlines will focus on signs of water ice and a possible ice-powered volcano, but the reports themselves really end up emphasizing how much we still don't know about the strange world. Despite all of Dawn's imaging, many features don't add up to a coherent picture of the body as a whole.

Before Dawn got there, our impression of Ceres was dominated by what we'd measured of its density. Those measurements suggested the dwarf planet has a substantial amount of water and is large enough to have differentiated, allowing rocky material to sink to the core. So we expected Dawn to find an icy world where viscous ice has gradually wiped away many of the indications of the impacts every Solar System body has suffered.

That's not at all what Dawn found. Instead, only the largest impact craters on Ceres seem to show any sign of viscous changes. This lack of viscous change suggests that Ceres' crust is much more rigid than it would be if it were comprised of water ice.

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http://arstechnica.com/science/2016/09/glut-of-papers-confirms-we-really-dont-understand-ceres/