21 years after the discovery of the last dwarf planet, scientists may have found a sixth one beyond Neptune

Vera Rubin Observatory may have identified a new dwarf planet called ED138, hidden beyond Pluto's orbit. Researchers are in the process of assessing ED138's size, a task expected to take several months. This finding is noteworthy as it holds the potential to be recognized as the sixth dwarf planet. Difficulties in locating such remote celestial bodies stemmed from their position in the southern hemisphere.

The Vera Rubin Observatory (VRO), located in Chile, has found its first potential dwarf planet circling the sun in the gelid abysses beyond Neptune. Named 2026 ED138, or simply ED138, the planet, which is way out beyond Pluto's orbit, would be one of the largest dwarf planets found beyond Neptune if confirmed. Also, it will be the sixth dwarf planet ever found and recognized by the International Astronomical Union, or IAU, joining the likes of Ceres, Pluto, Makemake, Haumea, and Eris.

Pluto was discovered as a planet in 1930, by astronomer Clyde Tombaugh at the Lowell Observatory, but the IAU demoted it as a dwarf planet 76 years after in 2006. But the most recent discovery of a dwarf planet is Makemake in the Kuiper Belt, and the second brightest object after Pluto. Makemake was discovered in March 2005 by a team led by Mike Brown at Palomar Observatory in California.

Five dwarf planets (NASA)

How ED138 discovered

Rubin Operations team member Matthew Holman was running data collected by Rubin earlier in 2026 through a search code he developed with CfA colleague Kevin Napier. The code looked at billions of moving objects and compared them, which eventually led to this discovery. Holman was able to distinguish it from its unusual brightness from a far distance, meaning it's large.

"My first reaction was one of excited disbelief," says Holman, who is also a Smithsonian senior astrophysicist and lecturer in astronomy at Harvard University. "Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong," he added in a statement.

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"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 in a statement to CNN.

How big and bright is ED138

Based on ED138's distance from Earth, brightness, and surface reflectivity, the researchers estimated that the diameter is estimated to be between 370 and 930 miles (600 and 1,500 kilometers), and icy bodies with this large size are expected to be round, they note.

With this dimension, ED 138 is poised to be bigger than the smallest recognized dwarf planets, Ceres, placed between Mars and Jupiter. It orbits the sun at a distance of about 46 astronomical units, and it is the only dwarf planet visited by a spacecraft, NASA's Dawn mission.

ED138 is not visible with the naked eye in the night sky, but "is bright enough that really capable amateurs can see it if they know where to look," Holman said to CNN.

Why could scientists not find ED 138 earlier?

Most of our major astronomical observatories are located in the Northern Hemisphere, and the potential dwarf planet beyond Neptune is in the southern hemisphere, which made it harder to spot it, as per Holman.

"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 explained to CNN.

ED138 is kept hidden because it is in the same plane as our galaxy, and scientists don't usually search for it. "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," Holman explained to the outlet.

The Rubin Observatory has the world's largest digital camera

The Vera C. Rubin Observatory, which houses the world's largest digital camera, is a relatively new telescope that sits atop an 8,800-foot-tall mountain in Chile and houses. It has been operating since last year and is capable of imaging the entire sky every three days.

"Rubin Observatory's super power is the ability to clearly capture movement and change among a vast number of objects and phenomena that humans have never seen before," Edward Ajhar, NSF Program Director for Rubin Observatory, said in the statement. "That power greatly extends our ability to reveal and understand new things about our Solar System, the Milky Way, and billions of other galaxies across the Universe."

"Rubin Observatory's unique strengths make it an incredible tool for investigating a wide range of astrophysical phenomena, from dark energy to the discovery of this dwarf planet candidate," says Kathy Turner, DOE's Program Manager for Rubin Observatory.

What could be the new name of ED 138?

The IAU adopted a new definition of a planet in 2006 when it set three criteria: it should orbit its own star, it should be round and big enough that its gravity cleared away any other objects of similar size near its orbit around the Sun. Following that, they stripped away Pluto's planet status because it didn't satisfy the last need.

If IAU confirms ED138 as the sixth dwarf planet, they will first assign a permanent number and then give it an actual name, which will take some time.

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