Vera Rubin Observatory discovers largest trans-Neptunian object candidate

The Vera C. Rubin Observatory has identified a potential dwarf planet designated 2026 ED138, located approximately 46 astronomical units from the Sun—beyond Pluto's orbit of 40 AU. The discovery was made by Matthew Holman of the Harvard-Smithsonian Center for Astrophysics while analyzing observational data collected between March and July 2026 during preparations for the observatory's Legacy Survey of Space and Time. Holman used automated search algorithms to identify moving objects within billions of detections and confirmed the find by locating 30 separate observations across 20 nights, extending the observation history back to 2016 using archival data.

The object is estimated to measure between 600 and 1,500 kilometers in diameter, potentially making it among the largest bodies discovered in the outer Solar System's trans-Neptunian region. Its orbital plane is tilted nearly 25 degrees relative to the ecliptic plane, suggesting gravitational interactions with Neptune displaced it from an original orbit. The object was detected in a crowded region near the Milky Way's galactic plane containing millions of stars, which explains why previous telescopes had not identified it. Rubin Observatory's combination of continuous southern-sky monitoring and advanced detection algorithms enabled the discovery where other instruments failed.

To confirm dwarf planet status, additional infrared observations are required to precisely determine the object's size, shape, and mass. The International Astronomical Union currently recognizes five dwarf planets: Pluto (reclassified from full planet status in 2006), Ceres, Eris, Haumea, and Makemake. If 2026 ED138 meets the criteria—sufficient mass to achieve hydrostatic equilibrium and a rounded shape—it would become the sixth recognized dwarf planet. The discovery demonstrates Rubin Observatory's capability to detect previously unknown distant solar system bodies; the facility has already contributed to locating approximately 2,300 trans-Neptunian objects since beginning operations.