Astronomers using the Vera C. Rubin Observatory in Chile have spotted a possible new dwarf planet beyond Pluto, in the observatory’s first dwarf planet candidate. The object, provisionally named 2026 ED138, was announced by the International Astronomical Union’s Minor Planet Center on 27 October 2026.
The object was identified on 13 October 2026 by Matthew Holman of the Center for Astrophysics at Harvard and Smithsonian, while running early Rubin observations through search code developed with Kevin Napier. The telescope recorded it 30 times on 20 nights between 4 March and 11 July 2026.
How big is it? Not yet known
2026 ED138 is currently about 46 astronomical units from the Sun, or about 6.88 billion kilometres, placing it beyond the orbit of Pluto. Its size has not been measured directly. Based on its distance, brightness and assumed surface reflectivity, the team estimates it is between 600 and 1,500 kilometres across, a range that would put it among the largest dwarf planet candidates ever found beyond Neptune.
That is an estimate, not a measured diameter. Infrared observations are needed to narrow the size and establish whether the object qualifies as a dwarf planet. If confirmed, it would join the five dwarf planets recognised by the International Astronomical Union: Pluto, Ceres, Eris, Haumea and Makemake. A preprint posted on 2 November 2026 traced the object across 89 years of archival observations, from a marginal 1937 photographic plate to survey images collected in 2026.
Why Rubin found it first
Rubin is an 8.4-metre telescope that surveys wide swaths of the southern sky, repeating observations every few days in preparation for the Legacy Survey of Space and Time, which began in June 2026. Its orbit is tilted almost 25 degrees off the plane of the solar system, suggesting it was disturbed by gravitational interactions with Neptune.
The object is the 14th brightest trans-Neptunian object found to date, and its absolute brightness places it among the ten intrinsically brightest known. Future occultations, when it passes in front of a distant star, should help reveal its true size. It takes about 280 years to circle the Sun once, on a mildly elliptical path about 6.5 billion kilometres in radius, and it was found against crowded star fields near the plane of the Milky Way, which makes the detection harder still. Rubin has already found a growing sample of solar system objects since it began collecting early data, and 2026 ED138, nicknamed “Ed” from its automatically generated identifier, is an early sign of what the full survey may uncover.
