Rubin Observatory Finds Possible New Dwarf Planet Beyond Pluto

Astronomers using the Vera C. Rubin Observatory have found an icy world beyond Pluto that could be large enough to count as a dwarf planet. If follow-up observations confirm it, the object, called 2026 ED138, would join a list that currently has only five members.

A Rare Find in the Outer Solar System

Matthew Holman of the Center for Astrophysics | Harvard & Smithsonian spotted the object on the evening of Oct. 13. He found it by running Rubin data through a search program he built with colleague Kevin Napier, which links detections of the same moving object across many images. The discovery was announced Oct. 27 by the International Astronomical Union’s Minor Planet Center and presented at a planetary science meeting in Spokane, Washington.

“Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong,” Holman said in a release.

ED138 sits about 46 astronomical units from the Sun, or roughly 4.3 billion miles. That’s farther out than Pluto’s average distance of about 40 au. Its size is estimated at 600 to 1,500 kilometers across, or roughly 370 to 930 miles, based on its distance and brightness. Mario Jurić of the University of Washington, who leads Rubin’s solar system science, called it the largest object of its kind found beyond Neptune in about 20 years.

Objects that large are expected to be round, which is one of the key requirements for dwarf planet status. Pluto, Ceres, Eris, Haumea and Makemake are the only dwarf planets currently recognized by the International Astronomical Union.

Why It Went Unnoticed for a Decade

Once Holman flagged the object, Jurić found 20 more observations in Rubin’s records. In total, Rubin captured ED138 30 times on 20 nights between March and July 2026. The team then found it in older images from the Dark Energy Camera going back to 2016, giving them more than 10 years of its orbit.

Earlier surveys likely missed it because it sits near the plane of the Milky Way, where crowded star fields make faint moving objects hard to pick out. Its orbit is also tilted about 25 degrees from the plane of the solar system. Astronomers think Neptune’s gravity likely pushed it off its original path long ago.

The Rubin Observatory, on a mountaintop in northern Chile, began its 10-year Legacy Survey of Space and Time in June. Even before the survey started, the team had already submitted more than 11,000 newly found asteroids to the Minor Planet Center, including about 380 objects beyond Neptune.

What’s Next

Astronomers will need infrared observations to pin down ED138’s true size and confirm it as a dwarf planet. “If confirmed as a dwarf planet, ED138 would join a very small family of worlds,” Holman said.

Rubin will keep scanning the southern sky every few nights for the next decade, and scientists expect it to turn up more objects like this one. Anyone curious can see where ED138 sits among the planets using Rubin’s free online Orbitviewer tool.

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