Rubin finds a dwarf planet candidate beyond Pluto

On the evening of 13 October 2026, Matthew Holman found a bright body beyond Pluto in data from the NSF-DOE Vera C. Rubin Observatory.

The object carries the provisional designation 2026 ED138, and only nine known trans-Neptunian objects are intrinsically brighter. The discovery team measures an absolute magnitude of 3.19, with an uncertainty of 0.04.

Holman is a senior astrophysicist at the Center for Astrophysics | Harvard & Smithsonian and a member of the Rubin operations team. He ran a search code he developed with Kevin Napier through Rubin detections collected earlier in 2026, before the Legacy Survey of Space and Time formally began. The code compares billions of detections of moving objects and keeps the ones that belong to the same body. Holman said his first reaction was one of excited disbelief, and that he checked at once whether he or the code had gone wrong. The Minor Planet Center announced the object on 27 October 2026. The discovery team identifies the circular as 2026-U85. Holman and Jurić presented the result that day at the 58th meeting of the Division for Planetary Sciences in Spokane, Washington.

Mario Jurić, the Rubin solar-system lead scientist and a faculty member at the University of Washington, then searched the catalogs. He found 20 further observations, the earliest on 4 March 2026. Rubin's Simonyi Survey Telescope recorded ED138 30 times on 20 nights from 4 March through 11 July. Images from the Dark Energy Camera on the Victor M. Blanco 4-meter telescope at Cerro Tololo, recovered by the Asteroid Institute's ADAM Precovery service, cover 14 nights from 2016 through 2023. The combined track covers more than 10 years of the orbit. The Department of Energy built that camera. Cerro Tololo is a program of NSF NOIRLab.

The team gives the orbit, measured from the Solar System's center of mass, a semi-major axis of 43.09 astronomical units, an eccentricity of 0.139, an inclination of 24.4 degrees, and a closest approach to the Sun of 37.1 astronomical units. One astronomical unit is the average distance from the Earth to the Sun. The observatory places the object about 46 astronomical units from the Sun at present, farther out than Pluto, whose average distance is 40 astronomical units, and beyond Neptune. That class of body is a trans-Neptunian object. The team classes the tilted orbit as hot-classical and reads the tilt as a sign that Neptune's gravity shifted it. The path sits near the 12:7 resonance with Neptune, the same neighborhood as the dwarf planet Haumea. About half of the orbits that still fit the data swing back and forth inside that resonance, so the team does not yet treat the membership as fixed. The color, a g minus r of 0.63, is redder than the Haumea family, so ED138 is not a fragment of that family.

A dwarf planet, on the definition used in the observatory's account, has to be massive enough for its own gravity to pull it into a round shape. The size depends on how reflective the surface is. For geometric albedos from 0.25 down to 0.04, the team estimates about 610 to 1,530 kilometers, and about 970 kilometers if the albedo is 0.10. Icy bodies in that range are expected to be round. The International Astronomical Union recognizes five dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris. ED138 stays a candidate until an albedo measurement or a stellar occultation fixes the size.

The object lay near the plane of the Milky Way, at a galactic latitude of about minus 12 degrees, a declination of about minus 43 degrees, and an i-band brightness of about 19.4. The field is full of stars, which is why earlier surveys either avoided it or covered it only shallowly. Rubin stands on Cerro Pachón in Chile and scans the southern sky with the largest camera yet built. The Legacy Survey of Space and Time began in June 2026 and is planned to run for ten years. In April, before the survey formally started, the solar-system team sent the Minor Planet Center observations of more than 11,000 new asteroids, about 380 of them trans-Neptunian. Holman said that if ED138 is confirmed it would join a very small family of worlds, and that a decade of repeated imaging should reach other large bodies in parts of the sky earlier surveys skipped.

Jurić said that once an object is identified, the same archive can be searched back through months and sometimes decades of images. It is the brightest trans-Neptunian object found since (532037) Chiminigagua in 2013. The images themselves are on the Rubin Science Platform for holders of Rubin data rights. The observations filed with the Minor Planet Center are public.