Researchers previously thought that Eris, a dwarf planet discovered in 2005, was larger than Pluto, partly because of the bright glow it gives off. Eris's size was part of the reason Pluto's planet status was taken away in 2006. Since then, researchers got a closer look at the icy Eris when it orbited past a dim star last year, according to a report from io9. Scientists had the opportunity to get better measurements of the dwarf planet, and now believe Pluto might actually be a hair bigger.
Because it's tricky to measure such massive bodies of matter light-years away, the results aren't certain.
"It could be smaller, it could be larger; basically, it is a twin," said Paris Observatory astronomer Bruno Sicardy, the lead researcher on the investigation, quoted in io9.
Still, after reviewing the data for about a year and going through the peer review process, scientists published the paper in Nature, concluding that Eris and Pluto are very close in size, but Pluto is probably the ninth-largest body orbiting the sun.
Whatever the true measurements are, scientists are certain of one thing - neither are ever going to join the planet club again.