Astronomers have reported the discovery of an icy object beyond Pluto's orbit that could join the official list of dwarf planets. The celestial body has received the preliminary designation 2026 ED138. It was spotted in data from the Simonyi Telescope at the NSF-DOE Vera Rubin Observatory.
The candidate was first seen by Matthew Holman, a senior astrophysicist at the Harvard-Smithsonian Center for Astrophysics. He was reviewing 2026 observations with a search program created together with colleague Kevin Napier. The program compares billions of recorded movements and finds those belonging to a single body.
"The first reaction was joyful disbelief," Holman said. "Such objects are very rare, so I immediately began checking whether I or the program had made a mistake." Mario Juric, a professor of astronomy at the University of Washington and head of the Solar System group in the Rubin project, found another 20 observations from March 2026 onward in catalogs and images. The object was also found in archival images from other surveys going back to 2016, which made it possible to trace more than ten years of its orbit.
2026 ED138 is currently about 46 astronomical units from the Sun. One such unit is the average distance from Earth to the Sun. Pluto orbits at an average distance of 40 units. The object is therefore classified as a trans-Neptunian body - one that moves beyond Neptune's orbit.
From the distance, brightness and estimated surface reflectivity, the team estimated the body's diameter at between 600 and 1,500 kilometers. Icy objects of this size are expected to be rounded. It is roundness under its own gravity that distinguishes a dwarf planet from other trans-Neptunian bodies. However, its exact dimensions have yet to be measured, and its dwarf planet status has yet to be confirmed.
If that happens, 2026 ED138 will join the five dwarf planets recognized by the International Astronomical Union: Pluto, Ceres, Eris, Haumea and Makemake. "Finding an object of this size - roughly 1,000 kilometers across - happens once in a generation," Juric noted. "It is the largest trans-Neptunian body found in the past 20 years, and Rubin discovered it while the telescope was still being commissioned."
The object was hiding in a region of the sky near the plane of the Milky Way, where there are many stars. For most telescopes it was lost among background sources - probably why it was not found earlier. Regular observations of the entire southern sky and powerful algorithms that select the needed points of light made it possible to notice the body in this dense region.
The results were presented at a press conference. The find added to the growing list of Solar System objects discovered by Rubin since the start of data collection for the Legacy Survey of Space and Time, a survey of space and time that began in June 2026. The team has previously reported new asteroids and trans-Neptunian objects, calling these discoveries "the tip of the iceberg."