In 2005, stargazing scientists discovered a previously unknown planet-like object, dubbed Eris, far off into the deepest reaches of our solar system in the Kuiper belt – even further away from us than Pluto. Its small size, then said to be marginally bigger than Pluto, caused some controversy in the scientific community, prompting Pluto’s famous demotion as a planet.
Now, studies have found that Eris isn’t actually that much different than Pluto. It’s smaller than originally thought, being just about the same size as Pluto is. Scientists previously thought of Eris as Pluto’s big sister, but now it looks like they’re icy twins.
Similar to Pluto, Eris orbits the sun in an “eccentric” orbit, meaning that it doesn’t circle around the sun in a circle, but rather more of an egg shape. At its furthest distance from the sun, Eris rests at around 9 billion miles away from the sun. In contrast, Pluto at its furthest distance is “only” 4.5 billion miles.
Also like Pluto, scientists believe that Eris has an off-and-on atmosphere. At its furthest point it’s too cold for an atmosphere to exist, but as it inches closer – at its closest, it gets within 3.4 billion miles from the sun – it’s believed that the atmosphere temporarily rises from the surface before freezing again as Eris gets further from the sun.
Another common trait between the two dwarf planets is that when their atmosphere freezes and falls to the surface, the planets get significantly brighter. Eris’ atmosphere is believed to be rich in methane, making it that much brighter at its furthest points from the sun when the atmosphere freezes and falls back to the surface.
[Image: Illustration of Pluto by L. Calçada, ESO]