Scientists may add a new dwarf planet to the official roster of our solar system.
The distant, icy body, provisionally dubbed 2026 ED138, orbits our system beyond Pluto. It was spotted earlier this month by a scientist combing through data from the Simonyi Survey Telescope at the NSF-DOE Vera C. Rubin Observatory. Initial measurements place ED138 among the largest dwarf planet candidates ever discovered beyond Neptune; if confirmed, it would join the five dwarf planets recognized by the International Astronomical Union: Pluto, Ceres, Eris, Haumea and Makemake.
The results were presented at a press conference today by Matthew Holman, a senior astrophysicist at the Harvard & Smithsonian Center for Astrophysics, and by Mario Jurić, a University of Washington professor of astronomy and leader of Rubin's solar system team. Holman first spotted the candidate and Jurić contributed additional observations.
"If confirmed as a dwarf planet, ED138 would join a very small family of worlds," Holman said. "Rubin will image the whole southern sky again and again for 10 years, so any others hiding in the places earlier surveys skipped are now within reach."
"Finding an object this big, roughly 1,000 kilometers across, is something that happens maybe once in a generation," Jurić said. "It's the largest trans-Neptunian object found in about 20 years, and Rubin turned it up while we were still commissioning the telescope."
On the evening of Oct. 13, Holman was running data collected by Rubin earlier in 2026 through a search code he developed with colleague Kevin Napier. The code is built to look at billions of detections of moving objects, compare them and find the detections that correspond to the same object. Using this method, Holman uncovered ED138, and he immediately noticed that its brightness and distance indicated that it is unusually large.
"My first reaction was one of excited disbelief," Holman said. "Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong."
To remove any doubt, Jurić searched through Rubin's catalogs and images and found 20 more observations, going back to March 2026. The team also spotted ED138 in archival images from other surveys going all the way back to 2016, allowing the team to trace more than ten years of ED138's orbit.
ED138 is currently at a distance of about 46 astronomical units (au), where 1 au is the average distance between the Earth and the sun. For reference, dwarf planet Pluto orbits at an average distance of 40 au. This classifies ED138 as a trans-Neptunian object (TNO) - objects that orbit the sun at a distance greater than Neptune's.
Scientists study the size, composition and orbital trajectories of TNOs to understand how the solar system formed, how the giant planets migrated over time and how smaller objects have been scattered throughout this evolution.
Not all TNOs are considered dwarf planet candidates, with the distinction being in the size and shape of the object. To be a dwarf planet an object needs to be massive enough for its own gravity to pull it into a round shape. Based on ED138's distance, brightness and estimated surface reflectivity, the team estimates that its size is between 600 and 1,500 kilometers; icy bodies this large are expected to be round. Further observations are needed to measure its exact size and confirm its nature as a dwarf planet.
ED138 was found in a region of sky close to the plane of the Milky Way - a crowded area filled with millions of stars. To most telescopes, ED138 has been lost among the myriad background sources, which is likely why it was not discovered until now. Rubin Observatory's regular and continuous monitoring of the entire Southern Hemisphere sky, combined with powerful algorithms that sift through millions to billions of points of light to identify those corresponding to small moving objects, enabled the team to spot ED138 within the crowded field.
ED138 joins the rapidly growing sample of solar system objects discovered by Rubin since it began collecting early data in preparation for the Legacy Survey of Space and Time (LSST), which began in June 2026. In April, before LSST formally began, the Rubin solar system team announced observations of over 11,000 new asteroids, which included roughly 380 new TNOs. At the time, the team called this large submission "the tip of the iceberg" and expressed their excitement for the discoveries to come once LSST began. With the discovery of ED138, those hopes are coming to fruition.
"Rubin is giving us an unprecedented capacity to explore the sky through a combination of speed, depth, and precision," Jurić said. "And the discovery is just the beginning: Once we identify a new object, we can search back months, and sometimes even decades, finding it in images where nobody knew to look. This ability to both discover and 'precover' objects is transforming how quickly and accurately we can determine their orbits and understand the distant solar system."
The public can interact with this discovery on Orbitviewer, an interactive web-based app that provides an intuitive way to explore the structure of our cosmic backyard in three dimensions and in real time.
Operations of the Vera C. Rubin Observatory are funded by the U.S. National Science Foundation and the U.S. Department of Energy's Office of Science.
