Rubin Observatory finds a possible new dwarf planet beyond Pluto
The object, provisionally named 2026 ED138, may be among the largest dwarf planet candidates ever found, but infrared observations are needed to confirm it.
AI illustrationThe NSF–DOE Vera C. Rubin Observatory has found a large object beyond Pluto that scientists have identified as a possible dwarf planet. The International Astronomical Union Minor Planet Center has given it the provisional designation 2026 ED138, or ED138, and announced the discovery on 27 October.
A preliminary analysis indicates that ED138 may be among the largest dwarf planet candidates ever found. If confirmed, it would join the five known dwarf planets: Pluto, Ceres, Eris, Haumea and Makemake.
Matthew Holman, a member of the Rubin Operations team at the Center for Astrophysics | Harvard & Smithsonian, spotted the object on the evening of 13 October. He was running Rubin data from earlier in 2026 through a search code he built with colleague Kevin Napier, which compares billions of detections of moving objects to find those that belong to the same body. Holman said its brightness and distance pointed to an unusually large object.
Mario Jurić, Rubin's Solar System lead scientist, then searched the observatory's catalogs and images and found 20 more observations. In total, Rubin's Simonyi Survey Telescope recorded ED138 30 times on 20 nights between 4 March and 11 July. Archival images from the Dark Energy Camera extended the record back to 2016, letting the team trace more than 10 years of the orbit.
ED138 is now about 46 astronomical units from the Sun, while Pluto's average distance is 40 au. Its orbit is tilted almost 25 degrees from the plane of the Solar System, which the team says suggests gravitational interactions with Neptune disturbed it from its original path.
Based on its distance, brightness and estimated reflectivity, the team estimates a size of between 600 and 1500 kilometers. Icy bodies of that size are expected to be round, a requirement for a dwarf planet. Infrared observations are needed to pin down its exact size and confirm its nature.
The object lies near the plane of the Milky Way, a part of the sky crowded with millions of stars, which is likely why it went unnoticed until now. Rubin's regular monitoring of the southern sky and its algorithms allowed scientists to pick it out. Observatories elsewhere can now carry out follow-up observations.
Rubin is jointly funded by the U.S. National Science Foundation and the U.S. Department of Energy's Office of Science. In April, the observatory submitted observations of over 11,000 new asteroids.