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The new moon, Eris, discovered by astronomers in the outer solar system which resulted in Pluto being ignominiously demoted to ‘dwarf planet’ status, has finally been weighed. It outweighs Pluto by a hefty 27 per cent. But it has only one moon compared to Pluto, which has three. As its diameter is slightly larger than Pluto’s, Eris was dubbed the ‘tenth planet’ when its discovery was announced in 2005. But following a debate over the definition of a planet, it became the largest "dwarf planet" — a new category of object that includes Pluto. For calculating Eris’ mass, Caltech researchers Michael Brown and Emily Schaller observed its moon, Dysnomia, over seven nights in 2005 and 2006 using the Keck Observatory in Hawaii, US, and the Hubble Space Telescope. The moon had a 15-day circular orbit, from which the team deduced Eris’ mass at 17 million trillion tonnes, making it 27 per cent more massive than Pluto. According to the team, since Eris is larger than Pluto in size—spanning 2400 km compared to Pluto’s diameter of 2320 km—its larger mass is not especially surprising. Nor is its density
surprising; it appears similar to Pluto’s, suggesting Eris is made
of rock and ice, they said. — ANI
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