Astronomers announced on Tuesday, Oct. 27, that the Vera C. Rubin Observatory in Chile has found a distant, icy body beyond Pluto that may be a dwarf planet, and one of the largest of its kind ever spotted. The object, provisionally designated 2026 ED138, was presented at the American Astronomical Society’s planetary sciences meeting in Spokane, Washington. It is the first dwarf planet candidate from a telescope that only began its 10-year survey in June.
The odd part is how long it had been sitting in plain view. Once the team knew where to look, they found it in survey images going back to 2016.
A bright object in the busiest part of the sky
Matthew Holman, a senior astrophysicist at the Harvard & Smithsonian Center for Astrophysics, found it on the evening of Oct. 13. He was running Rubin data from earlier this year through search software he wrote with his colleague Kevin Napier, which sifts billions of detections of moving points of light and links the ones that belong to the same object. One set stood out because its brightness and distance meant the object had to be unusually big. Holman said in the University of Washington’s release that his first reaction was “excited disbelief,” and that he started checking whether he or the code had made a mistake.
They hadn’t. Mario Jurić, the UW astronomer who leads Rubin’s solar system team, went back through the observatory’s own catalogs and found it in 20 more observations going back to March. A composite image released with the announcement shows it on Rubin frames taken between March 4 and July 11. Older images from other surveys, including the Dark Energy Camera on a different telescope in Chile, picked it up as far back as 2016, which gave the team more than a decade of its orbit.
Other surveys missed it because of where it sits. ED138 lies close to the plane of the Milky Way, a stretch of sky packed with millions of stars, and a slow-moving dot is easy to lose among them. Rubin photographs the whole southern sky every few nights, which is what lets software pick out the one point of light that moves. Holman told GBH News the object is bright enough that “really capable amateurs” could see it.
Somewhere between 600 and 1,500 kilometers
The headlines have mostly settled on one number. Jurić said in the release that an object “roughly 1,000 kilometers across” turns up “maybe once in a generation,” and called it the largest trans-Neptunian object found in about 20 years. The team’s own published estimate is much wider, between 600 and 1,500 kilometers.
The range comes from how the size is worked out. Astronomers can measure how much sunlight the object reflects and how far away it is, but not yet how reflective its surface is. Holman told GBH it could be “a very reflective object that’s smaller or a very dark object that’s bigger.” Even the bottom of that range is big enough that an icy body is expected to have pulled itself round, which is the test for a dwarf planet. Confirming it will take follow-up observations from other telescopes. ED138 is about 46 astronomical units from the Sun right now, where one unit is the Earth-Sun distance. Pluto’s average is about 40.
| Body | Found | Diameter | Status |
|---|---|---|---|
| Eris | 2005 | about 2,400 km | IAU dwarf planet |
| Pluto | 1930 | about 2,377 km | IAU dwarf planet |
| Haumea | 2003–04 | about 1,740 km at the equator (elongated) | IAU dwarf planet |
| 2026 ED138 | 2026 (in images from 2016) | 600 to 1,500 km (estimate) | Candidate |
| Makemake | 2005 | about 1,430 km | IAU dwarf planet |
| Ceres | 1801 | about 952 km | IAU dwarf planet |
The table places ED138 by its range. If it lands near the 1,000-kilometer figure, it would sit between Makemake and Ceres. The GBH report said the scientists count it among the seven largest objects found in the outer solar system so far.
“Sixth dwarf planet” depends on who’s counting
Several outlets have called ED138 a possible sixth dwarf planet. That counts only the five bodies the International Astronomical Union formally lists, which are Pluto, Ceres, Eris, Haumea and Makemake. Astronomers who study the outer solar system often count more. Live Science reported that many recognize nine, adding Quaoar, Sedna, Orcus and Gonggong, which the IAU has not formally added. On that count, a confirmed ED138 would be a tenth, not a sixth.
Either way, the IAU hasn’t confirmed anything yet. Its Minor Planet Center has so far given the object only a provisional designation.
Rubin’s first months
ED138 arrived early in the survey. In April, before the main survey began, Rubin’s solar system team reported more than 11,000 new asteroids, roughly 380 of them trans-Neptunian objects. Rubin’s 8.4-meter telescope feeds the largest digital camera built for astronomy, and ZME Science reported that it expects to revisit each patch of the southern sky about 800 times over the decade.
Napier told GBH that the Milky Way’s crowded fields have hidden objects for as long as astronomers have known about the Kuiper Belt, and that larger ones may still be waiting farther out, where they are fainter. ED138’s orbit can be explored in Rubin’s Orbitviewer app. The announcement is on the sites of NOIRLab, the University of Washington and the National Science Foundation.
Sources
- University of Washington News, “Rubin Observatory reveals its first dwarf planet candidate in our solar system” (Oct. 27, 2026). Used for: the Oct. 13 find, Holman and Napier’s code, Jurić’s 20 observations and quotes, the 2016 archival images, the 600 to 1,500 km estimate, the 46 au distance, the five IAU dwarf planets and the April asteroid count.
- U.S. National Science Foundation, “New dwarf planet candidate discovered by NSF–DOE Rubin Observatory” (Oct. 27, 2026). Used for: the provisional designation, the Milky Way field, the April asteroid count and Orbitviewer.
- GBH News, Craig LeMoult, “Potential new dwarf planet found by Harvard, Smithsonian astrophysicists” (Oct. 27, 2026). Used for: the Spokane meeting, Holman on size and amateur visibility, the “seven largest” ranking, the March 4 to July 11 composite and Napier’s comments.
- Gizmodo, Ellyn Lapointe, “Rubin Observatory Spots Possible Dwarf Planet Beyond Pluto” (Oct. 28, 2026). Used for: corroboration of the size range, distance and survey start.
- ZME Science, Tibi Puiu, “Astronomers Have Found a Possible New Dwarf Planet Beyond Pluto” (Oct. 28, 2026). Used for: the Dark Energy Camera images, Rubin’s mirror and camera, and the 800 revisits.
- Live Science, “What are dwarf planets, and how many are there?”. Used for: the five IAU-recognized dwarf planets and the nine astronomers commonly count.
- NASA Science fact pages for Pluto, Ceres, Eris, Haumea and Makemake. Used for: diameters and discovery dates in the table.