... Credit: Thierry Lombry Explanation: Eris , a dwarf planet currently orbiting the Sun at about twice Pluto's distance, has been measured to have about 27 percent more mass than Pluto. The mass was calculated by timing the orbit of Eris' moon Dysnomia . Images taken with a ground-based Keck telescope , when combined with existing images taken by Hubble Space Telescope , show that Dysnomia has a nearly circular orbit lasting about 16 days. ... Publications with keywords: Pluto - dwarf planet . ...