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The solar system's small club of dwarf planets may be about to gain a member. Astronomers using the new Vera C. Rubin Observatory in Chile have spotted an icy world beyond Pluto, provisionally named 2026 ED138, that is among the largest objects of its kind found in about 20 years. The discovery, announced on October 27 at a meeting of the American Astronomical Society's Division for Planetary Sciences in Spokane, is Rubin's first dwarf planet candidate — and, researchers say, almost certainly not its last.
A world hiding in the Milky Way's glare
ED138 was found by Matthew Holman, a senior astrophysicist at the Harvard & Smithsonian Center for Astrophysics, who was running a search program he developed with colleague Kevin Napier through Rubin data collected earlier in 2026. On the evening of October 13, the object popped up — and Holman's first reaction, he said, was "excited disbelief," followed immediately by checks for a false positive or a software error. There was none. Colleague Mario Jurić, Rubin's solar system lead scientist at the University of Washington, then found further observations of ED138 in Rubin's catalogues going back to March 2026, and the team traced it in archival images from other surveys going back to 2016 — more than a decade of positions, enough to pin down its orbit.
Part of why it stayed hidden so long is where it sits. As CNN reported, ED138 has spent the last 20 years looping across the band of the Milky Way from our point of view — lost in the crowd of background stars. Rubin, with the world's largest digital camera, could pick it out anyway.
How big, how far, how long
The numbers, as reported by the University of Washington and Reuters, are striking. ED138 is currently about 46 astronomical units from the Sun — 46 times Earth's distance, where Pluto averages about 40. Its diameter is estimated at between 600 and 1,500 kilometres (roughly 370 to 930 miles), making it potentially one of the largest dwarf planets known. Its orbit takes about 281 years and is tilted about 25 degrees to the plane of the solar system. Researchers believe it formed billions of years ago closer to the Sun before gravitational encounters with Neptune flung it outward.
That size matters for classification. To count as a dwarf planet rather than a large asteroid, a body must be massive enough for its own gravity to squeeze it into a roughly spherical shape. At ED138's estimated size, an icy body should clear that bar — but "should" is not "has." As Holman cautioned, "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." Confirmation will likely need observations from facilities like ALMA, the Atacama Large Millimeter/submillimeter Array, also in Chile.
Why Rubin changes the game
If confirmed, ED138 would join just five officially recognised dwarf planets: Ceres in the asteroid belt, and Pluto, Eris, Haumea and Makemake beyond Neptune. The deeper point is what Rubin represents. The NSF–DOE observatory atop Cerro Pachón in Chile, at 2,682 metres, images the entire visible sky every few days, and its 10-year survey of the southern sky only formally began in June 2026 — yet it had already detected more than 11,000 new asteroids before that start. "Finding an object this big, roughly 1,000 kilometres across, is something that happens maybe once in a generation," Jurić said. "It's the largest trans-Neptunian object found in about 20 years, and Rubin turned it up while we were still commissioning the telescope."
That is the real story here. ED138 is not just a possible sixth dwarf planet; it is proof that the outer solar system still holds large worlds we have simply never looked carefully enough to see. Rubin will image the whole southern sky again and again for a decade. As Holman put it, any others hiding in the places earlier surveys skipped "are now within reach." For more on how new worlds rewrite the textbooks, see our stories on the phoenix planet reborn from a dead star and NASA's Mars sample with potential signs of ancient life.