Astronomers have identified a previously unseen dwarf planet candidate orbiting beyond Pluto, opening another intriguing chapter in the effort to map the distant solar system. The object has been provisionally named ED138.

If additional observations confirm its status, ED138 would join the five dwarf planets currently recognized by the International Astronomical Union, or IAU. That group consists of Ceres, Pluto, Haumea, Makemake and Eris.

The discovery emerged from observations by the Vera C. Rubin Observatory, a new telescope positioned atop a 2,682 meter tall mountain in Chile. The observatory houses the world’s largest digital camera and can image the entire sky every three days.

Rubin began operating in 2025, and its ability to repeatedly survey huge areas of the sky is already producing detections. These include asteroids, much smaller trans-Neptunian objects and now the unusually large ED138.

Matthew Holman, a Smithsonian senior astrophysicist and lecturer in astronomy at Harvard University, used a computer program he codeveloped to examine Rubin data gathered earlier in 2026. The program scanned billions of detections involving moving objects.

When ED138 appeared, Holman initially responded with what he called “excited disbelief.” He immediately investigated whether the detection could be a false positive or an error produced by the program.

Holman, who is also a Rubin Operations team member, then worked with Mario Jurić, the Rubin Solar System lead scientist and a professor in the department of astronomy at the University of Washington. Jurić searched Rubin’s catalog and found 20 additional observations dating to March 2026.

Using information from other sources, the researchers were eventually able to trace the object’s orbit as far back as 10 years. Even with that evidence, Holman stressed that ED138 has not officially been classified as a dwarf planet.

“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,” Holman said.

Current estimates place ED138’s diameter between 600 and 1,500 kilometers, or 370 to 930 miles. That range could make it larger than Ceres, the smallest of the dwarf planets recognized by the IAU.

ED138 currently travels around the sun at a distance of about 46 astronomical units. Each astronomical unit represents the average distance between Earth and the sun, putting ED138 farther away than Pluto.

Its location also makes ED138 a trans-Neptunian object, a class of bodies that orbit the sun beyond Neptune. Although it cannot be seen with the naked eye, Holman said it “is bright enough that really capable amateurs can see it if they know where to look.”

ED138 remained hidden partly because it appears in the southern hemisphere, where fewer telescopes are searching the sky. Its position makes it especially difficult to observe from the northern hemisphere, eliminating entire groups of telescopes that might otherwise have detected it.

The object has also spent about 20 years appearing to move across the Milky Way from Earth’s perspective. Astronomers do not typically search that crowded region for moving objects because the enormous number of stars makes them difficult to identify.

Holman said there may be “a handful” of additional objects comparable in size to ED138, and he expects Rubin to eventually detect them. Megan Schwamb, a reader in astrophysics at Queen’s University Belfast and a member of the Rubin Solar System Operations team, said the observatory is surveying the solar system to new depths.

“I was surprised that it found such an object so early in the commissioning observations. This was not on my bingo card for this year,” Schwamb said. She added that Rubin’s speed, depth and sky coverage could transform scientists’ view of the solar system over the next decade, particularly during the next few years.

The IAU adopted a new definition of a planet in 2006, requiring such an object to orbit the sun, be mostly round and have cleared its orbit of similarly sized objects. Pluto failed the final requirement and was reclassified, reducing the solar system’s recognized planet count from nine to eight.

Dwarf planets are nearly round objects that orbit the sun but have not cleared their orbital regions of debris. If ED138 qualifies, astronomers would first assign it a permanent number and later an actual name, though that process could take time.

Michele Bannister, an associate professor at the University of Canterbury in New Zealand who was not involved in the discovery, described ED138 as scientifically important because it is both physically large and a trans-Neptunian object. Other telescopes will now investigate its size and physical characteristics.

“Maybe if we ever fly a spacecraft there, we’ll find it has a nitrogen glacier like Pluto,” Bannister said. “That would be great to see. But at the moment, all we know is that it’s big, and the rest is going to be speculation for a little bit, about what its physical characteristics really are.”