Pluto has company. Maybe.
What was found
On 27 October, astronomers announced 2026 ED138, a new object in the far outer solar system. It is about 46 times farther from the Sun than Earth is. Pluto, on average, sits at about 40.
Its size is between 600 and 1,500 kilometres across. Why such a wide range? "All we can see is how much light we're getting from it," said Matthew Holman of the Harvard & Smithsonian Center for Astrophysics. It could be small and shiny, or big and dark.
How it hid
It sits near the plane of the Milky Way, among millions of stars. Spotting one slow dot there is a cosmic "Where's Waldo", as Holman's colleague Kevin Napier put it.
The Vera C. Rubin Observatory in Chile changed that. Its 8-metre mirror photographs the whole visible sky about every three nights. On 13 October, Holman ran Rubin images through search software he built with Napier, which plays "connect the dots" with billions of moving specks. His first reaction, he said, was "excited disbelief."
Mario Jurić of the University of Washington then found 20 more sightings going back to March. Older archive images traced its path back to 2016.
Why it matters
"Finding an object this big, roughly 1,000 kilometers across, is something that happens maybe once in a generation," Jurić said. It's the largest object found beyond Neptune in about 20 years, and bright enough that skilled amateurs can see it.
It isn't a dwarf planet yet. Officially there are five: Pluto, Ceres, Eris, Haumea and Makemake. First astronomers need its real size. As Napier said: "Who knows what else will turn up?"