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    "headline": "Rubin Observatory finds its first dwarf planet candidate beyond Pluto; 2026 ED138 may be up to 930 miles wide",
    "description": "Rubin cameras caught the icy world 30 times on 20 nights this year, and archive images trace it back to 2016; it sits about 46 times farther from our star than Earth.",
    "datePublished": "2026-10-28T18:56:00+00:00",
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    "articleSection": "Science",
    "keywords": "2026 ED138, dwarf planet, Kuiper belt, Vera C. Rubin Observatory",
    "articleBody": "The NSF–DOE Vera C. Rubin Observatory has found its first dwarf planet candidate, an icy world called 2026 ED138 that may measure anywhere from 370 to 930 miles (600 to 1,500 kilometers) across and sits about 46 astronomical units from our star, well past Pluto. The International Astronomical Union’s Minor Planet Center announced the object on Tuesday, October 27, in an electronic circular, and the observatory’s team described the find in a release the same day. If its size holds up, ED138 would be one of the largest dwarf planet candidates ever found beyond Neptune. Only five bodies currently hold the official dwarf planet title: Pluto, Ceres, Eris, Haumea and Makemake. How a single code run on October 13 flagged 2026 ED138 The detection came from Matthew Holman of the Center for Astrophysics | Harvard & Smithsonian. On the evening of October 13 he fed images Rubin had taken earlier in 2026 into search software he wrote with colleague Kevin Napier. The program compares billions of detections of moving points of light and links the ones that belong to the same object. The object’s brightness and distance together pointed to something unusually big. “My first reaction was one of excited disbelief,” Holman said in the release. “Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong.” The check held up. Mario Jurić, Rubin’s solar system lead scientist at the University of Washington, dug through the observatory’s catalogs and turned up 20 more sightings. Rubin caught ED138 30 times on 20 nights between March 4 and July 11, 2026. Older frames from the Dark Energy Camera in Chile, located by the Asteroid Institute’s precovery service (a search of archives for an object nobody knew to look for), pushed the record back to 2016. That adds up to more than 10 years of positions. Why nobody spotted it sooner: ED138 lies close to the plane of the Milky Way, where its faint dot is buried among millions of stars. A 283-year orbit tilted almost 25 degrees ED138 is a trans-Neptunian object, meaning it circles our star beyond Neptune. Its path is tilted 24.4 degrees from the plane where the planets orbit, which marks it as a “hot classical” Kuiper belt object, one probably shoved off its original course by Neptune’s gravity. That matters because orbits like this help scientists work out how the giant planets migrated and scattered smaller bodies early on. Orbital solutions listed in the reference entry for 2026 ED138 put its closest approach to our star at 37.1 astronomical units and its farthest at 49, with one lap taking about 283 years. It last passed its nearest point around April 1926 and will return around April 2209. To put that distance in miles: the same entry gives the object’s average distance as 43 astronomical units, or 4.0 billion miles, which works out to about 93 million miles per unit. At today’s 46 units, ED138 is roughly 4.3 billion miles (6.9 billion kilometers) away. And the decade of observations covers only 10.37 years of a 282.68-year orbit, or about 3.7% of one circuit, so the solution will keep sharpening as the arc grows. Why the size estimate spans 600 to 1,500 kilometers Nobody has measured ED138 directly. Its size comes from how bright it looks, and that depends on albedo, meaning how much sunlight its surface reflects. A dark surface would mean a big body; a shiny one would mean a smaller body throwing back the same light. Icy bodies anywhere in that range are expected to be pulled round by their own gravity, the test for dwarf planet status, which is why the team calls it a candidate. Its absolute magnitude of 2.92 ranks it among the brightest objects known past Neptune, between the candidates Quaoar and Chiminigagua. ED138 also shows how fast Rubin is filling in the outer solar system. In April the observatory’s team reported more than 11,000 new asteroids, including roughly 380 trans-Neptunian objects found in under two months. About 5,000 such objects had been discovered over the previous three decades. What still has to be confirmed about 2026 ED138 The evidence is strong that the object exists and follows the orbit described: 30 Rubin sightings plus archival images spanning a decade. The size is a different matter. The team calls its analysis preliminary and says infrared observations are needed to pin down the diameter and confirm the object is a dwarf planet. Stellar occultations, when the object passes in front of a star, could fix its width, and high-resolution images from a telescope such as James Webb could reveal a moon, whose orbit would give its mass. So far the results have been shared through the circular and a release, and were presented by Jurić and Holman at a press conference during the 58th annual Division for Planetary Sciences meeting in Spokane, Washington. A permanent number, and then a mythological name, comes only after years of tracking. The public can follow the object’s path in Rubin’s Orbitviewer app, and the National Science Foundation says astronomers at other observatories can now plan follow-up observations. “Rubin will image the whole southern sky again and again for ten years, so any others hiding in the places earlier surveys skipped are now within reach,” Holman said. Further reading SLAC / Rubin Observatory: Rubin reveals its first dwarf planet candidate NSF: New dwarf planet candidate discovered by NSF–DOE Rubin Observatory Wikipedia: 2026 ED138 Image: Rubin Observatory/NSF/AURA/B. Quint, CC BY 4.0 via Wikimedia Commons This article was produced with AI assistance and reviewed by our Editorial Desk. How we work.",
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