Key Takeaways
- Rubin Observatory data revealed 2026 ED138, a trans-Neptunian object that may qualify as a dwarf planet.
- Preliminary estimates put its diameter between 600 and 1,500 kilometres, although its exact size remains uncertain.
- Archival observations traced its orbital history back to 2016, while infrared follow-up is needed to better establish its size and status.
A candidate world at the edge of the map
The NSF–DOE Vera C. Rubin Observatory in Chile has spotted its first dwarf planet candidate: 2026 ED138, a large trans-Neptunian object orbiting the Sun beyond Pluto. The International Astronomical Union's Minor Planet Center announced the find on October 27, 2026. If follow-up observations confirm it, ED138 would join a family that today has only five recognized members — Pluto, Ceres, Eris, Haumea and Makemake.
For now, ED138 remains a candidate: its size is estimated from its brightness and distance, and infrared observations are still needed to pin down its true dimensions and confirm that it qualifies.
Big, distant and tilted
ED138 is currently about 46 astronomical units from the Sun — farther out than Pluto's average distance of 40. Based on its brightness and estimated surface reflectivity, the team puts its size at 600 to 1,500 kilometres across, large enough that its own gravity should have pulled it into a round shape, and among the largest dwarf planet candidates ever discovered beyond Neptune.
Its orbit is tilted almost 25 degrees off the plane of the Solar System, making it a "hot classical" trans-Neptunian object — a sign that Neptune's gravity likely shoved it around early in Solar System history.
Found in data nobody was watching
Center for Astrophysics | Harvard & Smithsonian scientist Matthew Holman found ED138 on October 13, running a search code he developed with Kevin Napier to sift billions of detections for distant moving objects. Rubin's Simonyi Survey Telescope had imaged it 30 times on 20 nights between March 4 and July 11, 2026, and archival Dark Energy Camera images traced its orbit back to 2016 — a decade of hiding in plain sight.
It stayed hidden because it sits in a star-crowded patch of sky close to the plane of the Milky Way, lost among millions of background stars. Earlier in 2026, Rubin had already submitted more than 11,000 new asteroids to the Minor Planet Center, including roughly 380 trans-Neptunian objects.
The Twikup Take
Rubin's real trick is repetition: imaging the whole southern sky again and again for ten years, then letting algorithms catch what human eyes miss. One candidate dwarf planet in its first months of surveying suggests the outer Solar System's map is far from finished.