Astronomers have spotted a new dwarf planet candidate in the solar system, beyond the orbit of Pluto, which they have tentatively named ED138.
If future observations confirm the discovery, ED138 will join a group currently made up of five dwarf planets recognized by the International Astronomical Union, or IAU: Ceres, Pluto, Haumea, Makemake and Eris.
The discovery is the result of detections made by the Vera C. Rubin Observatory, a new telescope located atop a 2,682 meter high mountain in Chile and home to the world’s largest digital camera. The telescope began operating in 2025 and is capable of imaging the entire sky every three days.
Matthew Holman, senior astrophysicist at the Smithsonian and lecturer in astronomy at Harvard University, led a computer program he co-developed to comb through data collected by Rubin earlier in 2026, analyzing billions of moving object detections. When ED138 appeared, Holman said he initially reacted with “excited disbelief” and immediately checked to see if there was a false positive or error with the computer program.
To confirm the observation, Holman, who is also a member of the Rubin Operations team, worked with colleague Mario Jurić, Rubin’s principal solar system scientist and professor in the Department of Astronomy at the University of Washington. Jurić searched Rubin’s catalog for other observations of ED138 and found 20 additional ones dating back to March 2026. Eventually, using other sources, the researchers were able to trace the object’s orbit going back 10 years.
However, Holman cautions, ED138 is not yet officially a dwarf planet: “At this point, it’s still a candidate. We really need to know what its physical size is, and that will probably take a few months.”
ED138’s diameter is estimated to be between 600 and 1,500 kilometers (370 and 930 miles), which would make it larger than the smallest recognized dwarf planet, Ceres. It currently orbits the sun at a distance of approximately 46 astronomical units, with each unit representing the average distance between Earth and the sun. This means that ED138 is further away than Pluto and is also a trans-Neptunian object, or TNO, a class of objects that orbit the sun at a greater distance than Neptune.
In the night sky, ED138 is not visible to the naked eye but “is bright enough that really skilled amateurs can see it if they know where to look,” according to Holman.
Part of the reason scientists hadn’t discovered ED138 before is that it is in the Southern Hemisphere and therefore very difficult to observe from the Northern Hemisphere, Holman noted.
“That already rules out entire sets of telescopes that could have found this, and there aren’t that many telescopes scanning the skies in the southern hemisphere,” he said.
Another factor that hid ED138 is that it is on the same plane as our galaxy. “For 20 years, the object has been making a sort of loop through the Milky Way, from our point of view.“, Holman explained. “People don’t usually look for objects in the Milky Way, because there are so many stars that it’s very difficult to find moving objects.”
New candidate dwarf planet joins the Rubin telescope growing list of people detected objects – largely asteroids and much smaller TNOs. According to Holman, there could be “a handful” of additional objects the size of ED138, and Rubin should eventually find them as well.
“The Rubin Observatory is doing its job very well, inventorying the solar system at new depths,” said Megan Schwamb, reader in astrophysics at Queen’s University Belfast and member of the Rubin Solar System Operations team, in an email.
“I was surprised that he found such an object so early in the fielding observations. It was not on my bingo card for this year,” Schwamb added. “This shows how Rubin’s combination of speed, depth and sky coverage will transform our view of the solar system over the next decade and especially over the next few years.”
In 2006, the IAU adopted a new definition of planet, describing it as an object that orbits the sun, is primarily round, and is large enough to have cleared its orbit of similarly sized objects. Scientists made the controversial decision to demote Pluto because it didn’t meet the last requirement, and our solar system went from nine planets to eight.
At the same time, Pluto and its ilk became known as dwarf planets – nearly round objects that orbit the sun but are not large enough to have cleared their own orbits of debris.
If ED138 is confirmed as a new dwarf planet, astronomers will first give it a permanent number and then an actual name, although the process may take time and details on who exactly will choose the name are still unclear.
“People have already emailed me suggestions, and some of them are already picked up by other objects,” Holman said. “I don’t know. It’ll be fun. Maybe I can suggest something, but I’m not going to hold my breath because it’s a very big project.”
The discovery is important to the field, said Michele Bannister, an associate professor at the University of Canterbury in New Zealand, who was not involved in the discovery of ED138.
The object is “scientifically really cool because it’s a trans-Neptunian object and it’s also physically quite large, but still much fainter than what you can see with the naked eye,” said Bannister, who studies small worlds in the solar system.
The size of the object is just right In the range at which we can start to view it as a world, she added, and other telescopes will now take over to find out more.
“Maybe if we ever fly a spacecraft there, we’ll find that it contains a nitrogen glacier like Pluto,” Bannister said. “That would be great to see. But for now, all we know is that he’s tall, and the rest will just be a little bit of speculation about his physical characteristics.”
EDITOR’S NOTE: This story has been updated with additional information.
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