Rubin finds a possible dwarf planet beyond Pluto, up to 1,500 km across

NSF-DOE Vera C. Rubin Observatory has found 2026 ED138, an icy object beyond Pluto that NOIRLab says is a dwarf planet candidate. The team estimates it is 600 to 1,500 kilometers across. The International Astronomical Union’s Minor Planet Center announced the find on 27 October 2026.

Found by a search code, in the crowded band of the Milky Way

Matthew Holman of the Center for Astrophysics | Harvard & Smithsonian, a member of the Rubin operations team, spotted the object on the evening of 13 October. He was running data Rubin collected earlier in 2026 through a search code he built with colleague Kevin Napier. The code compares billions of detections of moving objects and links those that belong to the same body. Holman noticed at once that the brightness and distance made the object look unusually large.

“My first reaction was one of excited disbelief,” Holman said, adding that he started checking whether he or the code had made a mistake. Mario Jurić, Rubin’s Solar System lead scientist at the University of Washington, then searched Rubin’s catalogs and images and found 20 more detections going back to 4 March 2026. In total, Rubin saw the object 30 times on 20 nights between 4 March and 11 July.

Older images helped too. Archival pictures from the Dark Energy Camera on the Blanco 4-meter telescope in Chile, found through the Asteroid Institute’s ADAM Precovery service, reach back to 2016. Together they let the team follow more than 10 years of the object’s orbit.

The object lies in a part of the sky close to the plane of the Milky Way, where millions of stars crowd the background. NOIRLab says that most telescopes lose a faint moving dot there, which is likely why it went unnoticed until now.

What is known about its orbit and size

2026 ED138 is currently about 46 astronomical units from the Sun. One astronomical unit is the average Earth-Sun distance, so that is roughly 6.9 billion kilometers; Pluto averages 40 au. It is therefore a trans-Neptunian object, meaning one that orbits the Sun beyond Neptune.

Its orbit is tilted almost 25 degrees from the plane in which the planets travel. That makes it a “hot-classical” object, and NOIRLab says the tilt suggests gravitational interactions with Neptune disturbed it from its original path.

The size estimate comes from the object’s distance, its brightness and an assumed albedo, which is how much sunlight its surface reflects. Icy bodies of 600 km or more are expected to be pulled into a round shape by their own gravity, which is the test for a dwarf planet. Infrared observations are needed to pin down the real size and confirm the object’s nature.

How it would compare with the five known dwarf planets

If confirmed, 2026 ED138 would be the sixth dwarf planet recognized by the IAU, after Pluto, Ceres, Eris, Haumea and Makemake. The size range is wide enough that the ranking is still open. NASA gives Makemake a diameter of about 1,430 km and Haumea about 1,740 km at its equator, and puts Eris at about 2,400 km. At the low end of the estimate, 2026 ED138 would be well below all three; at the top end it would be close to Makemake.

Distance sets it apart as well. NASA lists Makemake’s average distance from the Sun at about 6.8 billion km, almost the same as the 6.9 billion km at which 2026 ED138 is now, while Eris averages about 10 billion km. Rubin’s contribution is to catch such a body in a part of the sky that earlier surveys found hard to search.

Jurić said that once a new object is found, the team can search back months, sometimes decades, in images where nobody knew to look. That “precovery” is what turns a few weeks of data into a usable orbit. NOIRLab also notes that in April, before the Legacy Survey of Space and Time began in June 2026, the Rubin team submitted over 11,000 new asteroids to the Minor Planet Center, including roughly 380 new trans-Neptunian objects.

Follow-up observations and public access

Holman said Rubin will image the whole southern sky repeatedly for ten years, so any other such bodies hiding in places earlier surveys skipped are now within reach. Astronomers worldwide can now plan follow-up observations. Images of the object are available to Rubin data rights holders on the Rubin Science Platform, and the public can follow its orbit in 3D on the Orbitviewer web app. Jurić and Holman presented the results at the 58th annual meeting of the American Astronomical Society’s Division for Planetary Sciences in Spokane, Washington.