Rubin Observatory Detects Candidate Dwarf Planet Beyond Neptune

The Vera C. Rubin Observatory has identified a distant object, 2026 ED138, that could be a new dwarf planet orbiting the Sun at about 46 astronomical units. The object's orbit is inclined roughly 25 degrees to the plane of the solar system, placing it in a region where background starlight from the Milky Way makes detection difficult.

Researchers used the observatory’s wide-field camera and automated detection software to compare billions of observations and isolate the moving source. By combining recent Rubin data with archival images from the Dark Energy Camera at the Victor M. Blanco Telescope, the team reconstructed the object's trajectory over the past decade.

Based on its brightness, estimated albedo and distance, the object's diameter is inferred to lie between 600 and 1,500 kilometres, a size range that overlaps the lower bound for recognized dwarf planets. For context, Pluto measures about 2,377 kilometres in diameter, while Ceres is about 958 kilometres.

"My first reaction was one of excited disbelief," said Matthew Holman, an astrophysicist at the Smithsonian Astrophysical Observatory and member of the Rubin team. "Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong."

"If confirmed as a dwarf planet, ED138 would join a very small family of worlds," Holman added.

The discovery comes early in the observatory’s planned ten-year sky-survey mission, which repeatedly images the entire southern sky and issues alerts for any objects that change brightness or position. Continued observations over the coming years are expected to refine estimates of the object's size and density, determining whether it meets the criteria for dwarf-planet status.