Possible Sixth Dwarf Planet ED138 Found Beyond Pluto in Rubin Data
Astronomers using the Vera C. Rubin Observatory in Chile have spotted a dwarf planet candidate beyond Pluto, provisionally named ED138. Researchers say it…
Scientists discover never-before-seen potential dwarf planet in the solar system, a distant object beyond Pluto that astronomers have provisionally named ED138. If follow-up observations confirm it, the object would become the sixth dwarf planet recognized by the International Astronomical Union (IAU).
The IAU currently recognizes five: Ceres, Pluto, Haumea, Makemake and Eris.
Found in Rubin data
The detections came from the Vera C. Rubin Observatory, a new telescope on a 2,682-meter (8,800-foot) mountain in Chile. It houses the world's largest digital camera and began operating in 2025. It can image the entire sky every three days.
Matthew Holman, a Smithsonian senior astrophysicist and lecturer in astronomy at Harvard University, ran a computer program he codeveloped on data Rubin collected earlier in 2026. The software scanned billions of detections of moving objects. When ED138 appeared, Holman said, he first felt "excited disbelief" and immediately checked for a false positive or a software error.
He then worked with Mario Jurić, the Rubin Solar System lead scientist and a professor of astronomy at the University of Washington. Jurić searched Rubin's catalog and found 20 additional observations of ED138 dating back to March 2026. Using other sources, the team plotted the object's orbit as far back as 10 years.
Still a candidate
Holman, who is also a Rubin Operations team member, stressed the status is not final. "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," he said.
The estimated diameter is between 600 and 1,500 kilometers (370 and 930 miles). That would make it bigger than Ceres, the smallest of the recognized dwarf planets. ED138 orbits the sun at about 46 astronomical units, each unit being the average distance between Earth and the sun. That puts it farther out than Pluto, and makes it a trans-Neptunian object, or TNO, a body orbiting beyond Neptune.
It cannot be seen with the naked eye. But it "is bright enough that really capable amateurs can see it if they know where to look," Holman said.
Why nobody saw it sooner
Two factors kept ED138 hidden, according to Holman. First, it lies in the southern hemisphere, which is very difficult to observe from the north. "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," he said.
Second, it sits on the same plane as our galaxy. "For the last 20 years, the object has kind of been looping its way across the Milky Way, from our point of view," Holman explained. "People don't typically search for things in the Milky Way, because there's so many stars that it's really hard to find moving objects."
More could follow
ED138 joins a growing list of objects detected by Rubin, mostly asteroids and much smaller TNOs. Holman said there might be "a handful" more objects the size of ED138, and Rubin should eventually find those too.
If the object is confirmed as a dwarf planet, astronomers will first assign it a permanent number and then a name. The process could take time, and who gets to choose the name is still unclear. Holman said people have already emailed him suggestions, and some are taken by other objects. "Maybe I'll get to suggest something, but I'm not going to hold my breath, because this is a big, big project," he said.
Source: cnn.com
