Will not so small after all Pluto now be reclassified as a planet?

Thursday, 18 November, 2010

Following recent observations, doubt has been cast over the size of Eris, a dwarf planet orbiting the Sun at a (massive) distance of up to 14,510,993,390 kilometres, and previously thought to be bigger than Pluto, a finding that eventually resulted in Pluto being classed as a dwarf planet in 2006, after being regarded as a planet since its discovery in 1930.

Occultation measurements are by their nature very accurate, and although more precision is needed before we get a definitive answer, Eris is certainly a lot smaller than it was thought to be. “Almost certainly Eris has a radius smaller than 1,170 km [727 miles],” Bruno Sicardy, of the Paris Observatory, said in an email to Sky and Telescope Magazine. Pluto has a radius of approximately 1,172 kilometers (728 miles). Pluto therefore has an average density of 2.03 grams/cm3 and Eris has an average density of 2.5 grams/cm3.

While the new figures don’t show a great deal of variance in the size of either object, they could re-open the discussion over whether Pluto should continue to be regarded as a dwarf planet.

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