Rubin Observatory Detects Possible New Dwarf Planet Beyond Pluto

Astronomers have identified ED138, a candidate dwarf planet beyond Pluto, using observations collected by the Vera C. Rubin Observatory in Chile during 2026. The object could become the solar system's sixth officially recognized dwarf planet if further research confirms its size and physical characteristics, expanding scientists' understanding of the distant outer solar system.

According to researchers, ED138 has an estimated diameter of 600 to 1,500 kilometers (370 to 930 miles). It orbits the sun at approximately 46 astronomical units, with each unit representing the average distance between Earth and the sun. The object is therefore farther from the sun than Pluto and belongs to the category known as trans-Neptunian objects.

Matthew Holman, a senior astrophysicist at the Smithsonian and a lecturer in astronomy at Harvard University, discovered the candidate while analyzing data from the observatory earlier in 2026. His computer program, developed with a colleague, searched billions of detections of moving objects. Holman initially described his reaction as "excited disbelief," prompting him to check whether the detection resulted from a false positive or a software error.

Holman, who is also a member of the Rubin Operations team, then worked with Mario Jurić, the observatory's solar system lead scientist and a professor in the University of Washington's astronomy department. Jurić located 20 additional observations of ED138 in the observatory's catalog, dating back to March 2026. Researchers combined those records with observations from other sources to trace the object's orbit as far back as 10 years.

Despite the evidence, Holman emphasized that the object's classification remains provisional.

"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," said Holman.

ED138 is not visible to the naked eye, although its brightness makes it accessible to some experienced amateur astronomers using suitable equipment. Holman explained that its position in the southern hemisphere has made observations difficult for researchers relying on telescopes in the northern hemisphere.

"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," said Holman.

The object's position against the Milky Way has also complicated detection because the dense concentration of stars makes moving objects harder to distinguish. Holman described how ED138's apparent movement across the galaxy had concealed it from searches over many years.

"For the last 20 years, the object has kind of been looping its way across the Milky Way, from our point of view," said Holman.

He explained that astronomers generally avoid searching crowded star fields when looking for faint objects moving through the solar system.

"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," said Holman.

The discovery adds to a growing catalog of solar system objects identified by the Rubin Observatory, including asteroids and smaller trans-Neptunian objects. Holman said the survey could eventually uncover several additional bodies comparable in size to ED138.

"a handful" more objects the size of ED138, said Holman, may eventually be found by Rubin.

Megan Schwamb, a reader in astrophysics at Queen’s University Belfast and a member of the Rubin Solar System Operations team, said the detection demonstrated the observatory's early capabilities. She noted that the discovery occurred during its commissioning observations, earlier than she had anticipated.

"Rubin Observatory is just doing its job really well, inventorying the Solar System to new depths," said Schwamb in an email.

Schwamb added that the finding illustrated how the telescope's observing speed, depth and broad sky coverage could improve solar system research during the coming years.

"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," said Schwamb.

"It shows how Rubin’s combination of speed, depth, and sky coverage is going to transform our view of the Solar System over the next decade and especially in the next few years," said Schwamb.

If astronomers confirm ED138 as a dwarf planet, the object will receive a permanent number before being assigned an official name. The naming process may take time, and the precise arrangements for choosing its name remain unclear.

Holman said he had already received suggestions for possible names, although some proposed names were already assigned to other objects.

"People have already emailed me some suggestions, and some of them are already taken by other objects," said Holman.

He also acknowledged that he might have an opportunity to propose a name but was uncertain whether he would participate in the process.

"I don’t know. It’ll be fun. Maybe I’ll get to suggest something, but I’m not going to hold my breath, because this is a big, big project," said Holman.

The International Astronomical Union currently recognizes five dwarf planets: Ceres, Pluto, Haumea, Makemake and Eris. Under the definition adopted by the organization in 2006, a dwarf planet orbits the sun and is nearly round but has not cleared its orbital neighborhood of other objects of comparable size.

The classification followed the IAU's decision to redefine the criteria for a planet, resulting in Pluto's reclassification and reducing the recognized number of planets in the solar system from nine to eight.

Michele Bannister, an associate professor at the University of Canterbury in New Zealand who was not involved in the discovery, highlighted the scientific importance of identifying a relatively large object so far from the sun.

"scientifically really cool because it’s a trans-Neptunian object and it’s also physically quite large, but still a lot fainter than you can see with the naked eye," said Bannister.

The Vera C. Rubin Observatory sits atop a 2,682-meter-tall (8,800-foot-tall) mountain in Chile and houses the world's largest digital camera. It began operating in 2025 and is designed to image the entire sky every three days, enabling researchers to identify and track objects across the solar system.