A Huge Possible Dwarf Planet Emerges in Rubin Observatory Data

On October 13, astronomer Matthew Holman found an unusually bright moving object hidden in data from Chile’s Vera C. Rubin Observatory. The object, now called 2026 ED138, may be 600 to 1,500 kilometres across, making it a strong dwarf planet candidate. Astronomers announced the discovery on October 27 but have not confirmed its status. ^1,2

Holman made the discovery while searching Rubin observations with software he built with colleague Kevin Napier. Holman is an astrophysicist at the Harvard & Smithsonian Center for Astrophysics. The program links points of light recorded on different nights to find moving objects. University of Washington astronomer Mario Jurić found more evidence in the observatory’s records: Rubin had captured ED138 30 times over 20 nights between March 4 and July 11, 2026. Older images showed it as far back as 2016. ^4,6

Those older images help explain why a potentially large world went unnoticed. ED138 lies near the Milky Way’s crowded band of stars, where its slow movement is hard to spot. It is about 46 times farther from the Sun than Earth, and its orbit tilts nearly 25 degrees from the solar system’s main plane. The size estimate depends on how much sunlight its surface reflects, so it could be smaller and brighter or larger and darker.^2,4,13 If its gravity has made it round, it could join Pluto, Ceres, Eris, Haumea and Makemake, the five dwarf planets recognized by the International Astronomical Union. ⁸

This possible sixth member also shows what Rubin’s repeated sky scans can do: find a faint moving object, then search old records to trace its path. Rubin’s 10-year survey is expected to find more objects in the outer solar system. For ED138, the next step is infrared follow-up, which should help scientists work out its size and decide whether it is round enough to qualify as a dwarf planet. ^1,8