Dwarf planet candidate discovered at the edge of the solar system

In the distant reaches of the solar system, beyond Pluto’s orbit, astronomers have found a celestial body that may be a dwarf planet. The object has been provisionally named ED138 and, if confirmed, could join the list of five officially recognized dwarf planets.

The observations that led to the discovery were made by the Vera C. Rubin Observatory, built on a mountain in Chile 2,682 meters above sea level. Equipped with the world’s largest digital camera, the observatory began operating in 2025. Its instruments can photograph the entire sky every three days, opening the way for searches for distant objects in the solar system.

Matthew Holman, a senior astrophysicist at the Smithsonian Institution and an astronomy lecturer at Harvard University, identified ED138 using a computer program he developed with colleagues. They analyzed data collected by the observatory during 2026. The program examined billions of alerts for moving objects before identifying the candidate.

Holman recalled that the news initially left him both excited and skeptical. He therefore checked whether it might be a false signal or a software error.

To verify the finding, Holman consulted his colleague Mario Juric, the scientist who leads solar system studies at the Rubin Observatory and a professor at the University of Washington. Juric searched the observatory’s catalog and found 20 additional observations of ED138 recorded since March 2026. Data from other sources helped the researchers trace its orbit back about 10 years.

ED138 cannot yet officially be called a dwarf planet, however. Researchers need to measure its physical size more precisely, which may require several more months of observations.

Dwarf planets are bodies that orbit the Sun and have enough mass to be nearly spherical, but have not cleared their orbits of other bodies. The five officially recognized by the International Astronomical Union are Ceres, Pluto, Haumea, Makemake and Eris.

Confirming ED138 and determining its size will help clarify the nature of this object beyond Pluto. The potential discovery also marks progress in studying the outer reaches of the solar system, where astronomers hope to find other previously undiscovered bodies through new observations and the analysis of vast amounts of data.