Astronomers Identify New Dwarf Planet Candidate Beyond Pluto
A candidate dwarf planet, provisionally named ED138, has been detected by the Vera C. Rubin Observatory and may join the five IAU-recognized dwarf planets pending size confirmation.
Astronomers using data from the Vera C. Rubin Observatory have identified a new dwarf-planet candidate, provisionally designated ED138, orbiting the Sun at roughly 46 astronomical units, beyond Pluto. The object’s estimated diameter of 600 to 1,500 kilometers would make it larger than Ceres, the smallest recognized dwarf planet.
The discovery resulted from a computer program co-developed by Smithsonian senior astrophysicist Matthew Holman, which scanned Rubin’s 2026 sky survey data. Holman and Rubin Solar System lead scientist Mario Jurić located 20 additional observations of ED138 dating back to March 2026, allowing them to reconstruct its orbit over the past decade.
"At this point, it’s still a candidate. We really need to know how physically big it is, and that will take a few months, probably," Holman said.
ED138 is a trans-Neptunian object that is not visible to the naked eye but can be detected by capable amateur astronomers with precise coordinates. Its location in the southern celestial hemisphere and its passage across the dense star fields of the Milky Way have likely contributed to its late detection.
"That already rules out whole sets of telescopes that might have found this, and there aren’t as many telescopes searching the sky in the southern hemisphere," Holman added.
If further observations confirm its size, the International Astronomical Union will assign ED138 a permanent number and eventually a name. Researchers anticipate that the Rubin Observatory may uncover additional objects of comparable size in the outer solar system.
Michele Bannister, an associate professor at the University of Canterbury who was not involved in the discovery, described the find as scientifically significant, noting that its size places it within the range of objects that could be considered worlds, though its physical characteristics remain uncertain.
"The object is scientifically interesting because it’s a trans-Neptunian object and it’s also physically quite large, but still a lot fainter than you can see with the naked eye," Bannister said.