An artist's concept of the dwarf planet Eris and its moon Dysnomia is seen in this undated illustration released by NASA. Most likely there is no liquid ocean inside Eris," Nimmo added. Eris has a diameter of about 1,445 miles (2,326 km), slightly smaller than Pluto's 1,473 miles (2,370 km). Because of its greater concentration of rock, which is denser than ice, Eris has about 25% more mass than Pluto. "Just like the Earth-moon system, tides on Eris slowly push Dysnomia away and slow down the spin of Eris.

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Persons: Pluto, Eris, Francis Nimmo, Nimmo, Mike Brown, Dysnomia, " Nimmo, Brown, we've, Will Dunham, Rosalba O'Brien Organizations: NASA, JPL, Caltech, Handout, REUTERS Acquire, Rights, of California, Astronomical Union, Thomson Locations: of California Santa Cruz, Neptune