Pluto has a twin: Icy dwarf planet Eris is almost exactly the same size



It was the discovery of Eris in 2005 that led to Pluto’s loss of planethood – and now astronomers have calculated that the two are doppelgangers.

Eris, which lies three times further from the Sun than Pluto, has finally been accurately measured by telescopes in Chile.



It turns out that its diameter is 1,445 miles, which is very similar to Pluto’s girth - between 1,429 and 1,491 miles.

Size matters: Eris was found to have almost exactly the same width as Pluto. Pictured is an artist's impression of the dwarf planet

The readings were made possible by Eris passing in front of a star – known in the business as a stellar occultation - which allowed astronomers to get a good look at it.

Until this happened it just appeared as a faint light, even using powerful equipment.



Twenty-six telescopes around the world were asked to be on the lookout for the event, but only three in Chile managed to do so, in November 2010, including the TRAPPIST telescope at the European Organisation for Astronomical Research's La Silla Observatory.

What they observed was very surprising, because Eris should have been a lot bigger.

Named after the Greek goddess of chaos and strife, it lies in the far-off Kuiper Belt beyond Neptune in a 557-year orbit. This is about 4.5billion miles from the Sun - and yet it’s a very bright object, reflecting all of the light thrown at it.

Lighting the way: In an image provided by the W.M. Keck Observatory in Kamuela, Hawaii, Eris appears in the centre, while its moon is the small dot at the 3 O'clock position

This led astronomers to believe it would be a fair bit more massive than Pluto, which is a much cosier 3.67billion miles from the solar system’s star.

They now think that Eris’s glow comes from a thin methane-and-nitrogen frost layer that’s wrapped around its surface, which is brighter than fresh snow on Earth.



Analysis of the dwarf planet was undertaken by a team at the Pierre et Marie Curie University and Observatory of Paris and the results published in Nature.

It’s the most distant object in the solar system ever measured using star-light wobble and lead researcher Bruno Sicard hailed the event as an exciting breakthrough.

He said: ‘It is extraordinary how much we can find out about a small and distant object such as Eris by watching it pass in front of a faint star, using relatively small telescopes.