Eris, the dwarf planet discovered in 2005, has passed in front of a star and is providing astronomers with the clearest view of it since it was identified.
The planets size and other characteristics have been difficult to measure because it is located nearly three times farther from the sun than Pluto and about 96 times farther from the sun than the Earth. However, astronomers were able to gather new data using two telescopes in Chile including the Belgian TRAPPIST telescope at ESO’s La Silla Observatory, as Eris passed in front of a faint star in 2010.
Previous methods of measurement suggested that Eris was probably about 25% larger than Pluto with an estimated diameter of 1900 miles; according to the new analysis the two objects are essentially the same size. Eris’s newly determined diameter stands at 1445 miles, with an accuracy of 7.5 miles.
This makes its size better known than that of its closer counterpart Pluto, which has a diameter estimated to be between 1429 and 1491 miles. The planet appears to have a very reflective surface, suggesting that it is uniformly covered in a thin layer of ice, probably a frozen atmosphere.
Based on the new measurements, and combined with data from NASA’s Spitzer space telescope and ESA’s IRAM scientific satellite, the researchers estimate that the surface temperature on the side of Eris facing the sun is no more than –238 C.
Eris is one of the brightest objects in our solar system. Its discovery was one of the factors that led to the creation of a new class of objects called dwarf planets and the reclassification of Pluto from planet to dwarf planet in 2006. The research is published in today’s issue of the journal Nature.