Astronomers announced on Oct. 27 a dwarf planet candidate, 2026 ED138, about 46 astronomical units from the Sun and an estimated 600 to 1,500 kilometers across, found in data from the NSF–DOE Vera C. Rubin Observatory, according to the SLAC release.
Matthew Holman found the object on the evening of Oct. 13, 14 days before the announcement, a calculation from the two dates. Discovery went fast, and confirmation will not: the size range spans a factor of 2.5, and it has to narrow before astronomers can call the object a dwarf planet.
How Rubin Found 2026 ED138
Holman, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, used a search code he developed with colleague Kevin Napier that compares billions of moving-object detections. Napier described the method to GBH News as playing “connect the dots” with detections that might be moving. Holman said his first reaction was “excited disbelief.”
Rubin observed the object 30 times on 20 nights between March 4 and July 11, 2026. Mario Jurić, the observatory’s solar system lead scientist, found 20 more observations in Rubin’s catalogs. Archival images from the Dark Energy Camera reach back to 2016, which let the team trace more than 10 years of the object’s orbit.
What is Known about the Orbit and Size
The object sits about 46 astronomical units from the Sun, against an average of 40 for Pluto, which puts it 15% farther out by a calculation from the two figures. It is a trans-Neptunian object with an orbit tilted almost 25 degrees from the plane of the solar system, which classifies it as hot-classical and suggests Neptune’s gravity disturbed its original path.
The size estimate comes from distance, brightness and an assumed albedo, the share of light a surface reflects. Icy bodies this large are expected to be round. The International Astronomical Union recognizes five dwarf planets: Pluto, Ceres, Eris, Haumea and Makemake.
What Confirms a Dwarf Planet
Infrared observations are needed to narrow the size and settle the object’s status. The Minor Planet Center announced the discovery in a circular, and confirmation is pending. Edward Ajhar, the National Science Foundation’s program director for Rubin Observatory, said Rubin’s ability to capture movement and change across many objects is a major strength, and Jurić said the team can search older images once an object is found. Researchers with data rights can pull the images from the Rubin Science Platform, and the public can view the orbit on Orbitviewer. Rubin will keep scanning the southern sky for 10 years.
