Astronomers sorting through data from the Vera C. Rubin Observatory in Chile have found a strong candidate for a new dwarf planet in the outer solar system, an icy world beyond Pluto provisionally named 2026 ED138. If confirmed, it would become only the sixth dwarf planet officially recognised by the International Astronomical Union, joining Pluto, Ceres, Eris, Haumea and Makemake.
The discovery was announced on October 27, 2026, by the International Astronomical Union Minor Planet Center, after the object was spotted in observations taken by Rubin in the run-up to its ten-year Legacy Survey of Space and Time. It is the observatory’s first dwarf planet candidate, and scientists say it may be among the largest and brightest objects ever found in the region beyond Neptune.
Key Takeaways
- The Vera C. Rubin Observatory has spotted 2026 ED138, a large, bright trans-Neptunian object that scientists have identified as a dwarf planet candidate.
- ED138 currently orbits about 46 astronomical units from the Sun, beyond Pluto’s average distance of 40, and is estimated to be between 600 and 1,500 kilometres across.
- The object is still a candidate, not a confirmed dwarf planet: infrared observations are needed to pin down its exact size and confirm its nature.
How the new world was found
The find was made by Rubin Operations team member Matthew Holman, of the Center for Astrophysics at Harvard and Smithsonian, using search code he developed with colleague Kevin Napier. The code is built to sift through billions of detections of moving objects, compare them, and find the detections that correspond to the same object.
On October 13, the code flagged an object so bright and distant that it was likely unusually large. Holman’s first reaction, he said, was excited disbelief, and he immediately checked for a false positive or an error in the program. To remove any doubt, Mario Jurić, Rubin’s solar system team leader and a University of Washington astronomy professor, searched Rubin’s catalogues and images and found 20 more observations going back to March 2026. The team also spotted ED138 in archival images from other surveys going back to 2016, allowing them to trace more than ten years of its orbit.
If confirmed as a dwarf planet, ED138 would join a very small family of worlds.
Why it stayed hidden for so long
Scientists at the observatory think ED138 evaded detection until now because it was found in a region of sky close to the plane of the Milky Way, where observers had to pick it out from the light of billions of stars. Rubin’s regular, continuous monitoring of the southern sky, combined with algorithms that sift through millions to billions of points of light, made it possible to spot the object within that crowded field.
The observatory, jointly funded by the US National Science Foundation and the Department of Energy, sits on a remote hilltop in Chile and carries the 3,200-megapixel Legacy Survey of Space and Time camera, which came online in June 2026. Even before that official start, the Rubin team had already detected more than 11,000 new asteroids, and ED138 is described as the largest trans-Neptunian object found in about 20 years.
How big is it, and what would confirmation take?
Based on its distance, brightness and estimated surface reflectivity, the team estimates ED138 is between 600 and 1,500 kilometres across. If the lower number is correct, it would be the smallest dwarf planet yet observed; if the larger number is correct, it would be smaller than Pluto, Eris and Haumea but larger than Makemake and Ceres. Either way, it would rank among the largest dwarf planet candidates ever discovered beyond Neptune.
That range is also why the word candidate matters. The International Astronomical Union defines a dwarf planet as an object in orbit around the Sun that is large enough to pull itself into a nearly round shape but has not been able to clear its orbit of debris. Infrared observations are still needed to constrain ED138’s exact size and confirm that it meets that definition, a process Holman has said will probably take a few months.
- Designation: 2026 ED138, a provisional name assigned by the International Astronomical Union Minor Planet Center
- Distance: about 46 astronomical units from the Sun, beyond Pluto’s average of 40
- Estimated size: between 600 and 1,500 kilometres across
- Found by: Matthew Holman, using search code developed with Kevin Napier, on data from the Vera C. Rubin Observatory in Chile
- Status: dwarf planet candidate only — confirmation needs infrared observations to pin down its size
- Context: if confirmed, it would join Pluto, Ceres, Eris, Haumea and Makemake as the sixth recognised dwarf planet
A window into the early solar system
Astronomers suspect ED138 formed billions of years ago closer to the Sun before being flung into a wider orbit by gravitational interactions with Neptune, and its tilted orbital path takes it well beyond Pluto. Studying such objects helps researchers understand how the outer solar system took shape, and each new large body found in the region adds a piece to that picture.
The discovery also shows what Rubin’s decade-long survey of the southern sky is expected to deliver. The observatory is designed to image the entire sky every few days, and its team expects ED138 to be the first of many distant finds rather than a one-off, with more faint, far-flung objects likely to emerge as the survey builds up its catalogue of the night sky — much as other space missions, from NASA’s Mars exploration to new AI-driven work in space, keep expanding what astronomers can see and measure, alongside milestones such as India’s latest navigation satellite launch.
What to Watch Next
Attention now turns to the infrared observations needed to constrain ED138’s exact size and confirm whether it qualifies as a dwarf planet, a process expected to take months. Beyond that, researchers will watch whether Rubin’s ongoing survey turns up further large trans-Neptunian objects, and whether ED138 takes its place alongside Pluto, Ceres, Eris, Haumea and Makemake on the official list.