Eris is Pluto's twin

French, Belgian, Spanish and Brazilian astronomers, using telescopes installed in Chile (ESO's 2.2-meter La Silla Telescope and others), for the first time were able to accurately measure the diameter of the dwarf planet Eris, observing its passage against the background of a faint star (published in Nature October 27, 2011). This event occurred at the end of 2010. Observations show that Eris is an almost perfect twin of Pluto in size (2326 km with an accuracy of 12 km, while Pluto’s diameter is 2300-2400 km), and its surface is covered with a frozen atmosphere and very well reflects light (albedo 0.96, while the Moon has only 0.136). However, by studying the movement of the satellite Eris Dysnomia, it was possible to find out that the mass of this dwarf planet is 27% greater than the mass of Pluto (it is 1.66 x 1022 kg, which corresponds to 22% of the mass of the Moon). Thus, Eris's density is estimated at 2.52 g/cm3, and it contains much more rock than ice.

M.B.
Photo - ESO