Possible dwarf planet found beyond Pluto

Astronomers using the Vera C. Rubin Observatory in Chile have spotted a possible new dwarf planet orbiting beyond Pluto, provisionally named ED138, according to a report from CNN published by CTV News on Oct. 28.

The object is a candidate only. If later observations confirm it, ED138 would become the sixth dwarf planet recognized by the International Astronomical Union, joining Ceres, Pluto, Haumea, Makemake and Eris, CNN reported.

Its diameter is estimated at between 600 and 1,500 kilometres, which would make it larger than Ceres, the smallest recognized dwarf planet, CNN reported. It currently orbits the sun at about 46 astronomical units, meaning 46 times the average distance between Earth and the sun. That puts it farther out than Pluto, which averages about 40 astronomical units, and makes it a trans-Neptunian object, a class of bodies that orbit beyond Neptune.

Matthew Holman, a Smithsonian senior astrophysicist and Harvard lecturer who is also a member of the Rubin operations team, found the object while running a computer program he co-developed to comb through billions of moving-object detections in data the telescope collected earlier this year. He said he first reacted with “excited disbelief” and checked for a false positive or a software error.

Mario Jurić, the Rubin solar system lead scientist and a University of Washington professor, then searched the observatory’s catalogue and found 20 additional observations dating back to March 2026. Using other sources, the researchers plotted the orbit as far back as 10 years, CNN reported.

“At this point, it’s still a candidate,” Holman said. “We really need to know how physically big it is, and that will take a few months, probably.”

The object is not visible to the naked eye but is bright enough that “really capable amateurs can see it if they know where to look,” Holman said.

He said it went unnoticed partly because it sits in the southern sky, which is harder to observe from the northern hemisphere and has fewer telescopes searching it. It has also spent the past 20 years crossing the Milky Way from Earth’s point of view, where the dense field of stars makes moving objects hard to find, Holman said.

Holman said there may be “a handful” more objects of similar size that Rubin should eventually find. Megan Schwamb, an astrophysicist at Queen’s University Belfast and a member of the Rubin solar system team, said the telescope’s combination of speed, depth and sky coverage will transform the view of the solar system over the next decade.

The International Astronomical Union adopted its current definition in 2006: a dwarf planet orbits the sun, is nearly round, but has not cleared its orbit of other objects. That definition led to Pluto being reclassified. If ED138 is confirmed, it would first receive a permanent number and later a name, a process that could take time, and Holman said it is unclear who would choose the name.

Other outlets, including CBC News and U.S. News, also reported the Rubin Observatory finding, which was announced Oct. 27.

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Sources: CNN via CTV News, CBC News, U.S. News. Photo: File photo of the Vera C. Rubin Observatory under construction in Chile in 2021, Rubin Observatory/NSF/AURA, CC BY 4.0; it does not show ED138.