The solar system’s exclusive club of dwarf planets may be about to gain a member. Astronomers using the Vera C. Rubin Observatory in Chile have found a large icy body far past Neptune, provisionally named 2026 ED138, and unveiled it at the American Astronomical Society’s planetary sciences meeting in Spokane, Washington.
Credit for the discovery goes to Matthew Holman, an astronomer at the Harvard-Smithsonian CfA. On the evening of October 13 he fed this year’s Rubin data into software he wrote with colleague Kevin Napier, a program that sifts billions of detections to work out which dots belong to the same moving object. One of them stood out for being both bright and remote, a sign of serious size. “My first reaction was one of excited disbelief,” Holman said, adding that he immediately went hunting for a mistake.
There was none. Rubin had imaged the object 30 times across 20 nights between March and July, and archive pictures from the Dark Energy Camera traced it back to 2016. National Geographic reports it may even appear on plates from 1954. Today it sits about 46 astronomical units from the Sun, compared with an average of around 40 for Pluto.
Its exact size is still uncertain. Depending on how reflective the surface is, estimates range from roughly 600 to 1,500 kilometers across, and icy worlds that big are expected to have pulled themselves into a sphere. If follow-up observations confirm that, ED138 would become the sixth officially recognized dwarf planet, joining Pluto, Eris, Makemake, Haumea and Ceres.
Researchers see it as a preview. Over its ten-year sky survey, Rubin is expected to catalogue tens of thousands of objects beyond Neptune, and a few more dwarf planets could be hiding among them.
