SPOKANE, 28 October 2026 — Astronomers using the Vera C. Rubin Observatory in Chile have found a large icy world far beyond Pluto that may become the solar system's sixth recognised dwarf planet, announcing the candidate, provisionally named 2026 ED138, on 27 October 2026 at a meeting of the American Astronomical Society's Division for Planetary Sciences.
Illustration: A large observatory telescope dome on a Chilean mountaintop under a starry night sky, representing the sky survey that found the distant world.
What Happened
The discovery was announced on Tuesday by University of Washington astronomer Mario Jurić, the Rubin team's solar system lead scientist, together with Matthew Holman of the Harvard and Smithsonian Center for Astrophysics, who first identified the object. Holman found it by running billions of detections collected by the Rubin Observatory through a search code he developed with Kevin Napier, designed to link faint moving dots across many images into a single orbit.
The object, known for now only by its provisional designation 2026 ED138, currently sits about 46 astronomical units from the Sun — one astronomical unit being the average distance between Earth and the Sun. Pluto, by comparison, is currently about 40 astronomical units away, and the new object's orbit is tilted by roughly 25 degrees relative to the plane of the planets.
Based on its distance, brightness and estimated surface reflectivity, researchers estimate that 2026 ED138 is between about 600 and 1,500 kilometres across. Icy bodies this large are expected to be round, pulled into a near-spherical shape by their own gravity — and roundness is the key test for dwarf planet status.
Confirmation, however, is still to come. Astronomers have called 2026 ED138 a dwarf planet candidate, not a confirmed dwarf planet. Establishing that its gravity has indeed shaped it into a near-spherical body will require follow-up imaging and measurements of its size and mass, and researchers say further study could also reveal more large objects hiding in similar crowded regions of sky.
Background
A dwarf planet, under the definition adopted by the International Astronomical Union, orbits the Sun, is massive enough for its own gravity to make it nearly round, but has not cleared its orbital neighbourhood of other objects — the criterion separating dwarf planets from the eight major planets. Five bodies currently hold the status: Pluto, Ceres, Eris, Haumea and Makemake. Pluto, reclassified from planet to dwarf planet in 2006, remains the best known of the group.
The outer solar system beyond Neptune is populated by thousands of icy remnants left over from the solar system's formation, most of them small and faint. Finding the large ones is difficult, and 2026 ED138 illustrates why: it had been hiding in the light of the Milky Way's stars, in a dense starfield whose glare masked faint moving targets from earlier searches. It escaped detection until now not because it is especially small, but because it sits in one of the busiest patches of sky.
The discovery was made possible by two things working together: the Rubin Observatory itself, a joint United States National Science Foundation and Department of Energy project in Chile, whose large mirror and wide field of view photograph huge areas of sky in great depth; and the search software, which combed survey images taken earlier in 2026 — during the run-up to Rubin's decade-long Legacy Survey of Space and Time — and linked more than 30 Rubin observations from March to July 2026 with archival sightings back to 2016. That technique, known as precovery, reconstructed the object's orbit from images taken years before anyone knew it was there.
Mario Jurić, announcing the find, said Rubin was giving astronomers an unprecedented capacity to explore the sky through a combination of speed, depth and precision, and that the ability to both discover new objects and recover them in old images was transforming how quickly and accurately their orbits could be determined.
Illustration: A distant icy dwarf planet glowing faintly far beyond Neptune's orbit, with the Sun a tiny bright point far away.
Why It Matters
The find matters first because it suggests the census of the outer solar system is still incomplete — even for large objects. If a world hundreds of kilometres across can hide in a crowded starfield until a new telescope and a new search code come along, then other substantial bodies may be waiting in similar blind spots. Each new large object refines our picture of how much material the outer solar system contains and how it is distributed.
It also matters as a demonstration of what the Rubin Observatory era will bring. Rubin is designed to survey the entire southern sky repeatedly over ten years, recording everything that moves or changes. The 2026 ED138 discovery came from data gathered before that main survey had even begun in earnest, which suggests the full survey could turn up many more distant objects and pin down their orbits quickly through precovery in its own growing archive.
There is a scientific payoff beyond the headcount. The size, orbit and composition of large trans-Neptunian objects carry clues about the early solar system: how the giant planets migrated and how the distant icy reservoirs formed. A tilted orbit like that of 2026 ED138 is itself a clue, since objects thrown onto inclined paths preserve a record of gravitational encounters long ago.
Finally, the discovery has a cultural resonance few astronomy stories match. Pluto's demotion in 2006 made the dwarf planet family a household topic, and the prospect of a sixth member — a new sibling for Pluto, Ceres, Eris, Haumea and Makemake — captures the imagination in a way that a catalogue entry for a small asteroid never could.
What Happens Next
Astronomers will now pursue the follow-up observations needed to confirm 2026 ED138's status: measuring its size more precisely, testing whether it is indeed round, and refining its orbit. If the evidence supports dwarf planet status, the object would go through the usual naming process for such bodies, replacing its provisional designation with a permanent name drawn, by tradition, from mythology.
The discovery is also expected to spur searches of Rubin's existing data for other hidden objects. The same combination of deep, wide-field images and linking software that found 2026 ED138 in a Milky Way starfield can be turned on other crowded regions of sky, and researchers have suggested that further large finds may follow. The full Legacy Survey of Space and Time, once under way, will multiply the data available for such hunts many times over.
For now, though, the announcement stands as a candidate, not a coronation. The object is real, its orbit is increasingly well determined, and its size range points strongly towards a round world — but astronomy's rules require the roundness to be shown, not assumed.
Illustration: A giant telescope scanning a dense field of Milky Way stars, with a small moving icy world among them.
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FAQ
What is 2026 ED138?
2026 ED138 is a newly announced dwarf planet candidate in the outer solar system, found in data from the Vera C. Rubin Observatory in Chile. It is a large icy trans-Neptunian object currently about 46 astronomical units from the Sun, beyond Pluto's present distance of about 40 astronomical units.
Who discovered it, and when was it announced?
It was identified by Matthew Holman of the Harvard and Smithsonian Center for Astrophysics, using a search code he developed with Kevin Napier, and announced on 27 October 2026 at a meeting of the American Astronomical Society's Division for Planetary Sciences in Spokane, Washington, together with Rubin solar system lead scientist Mario Jurić.
How big is it?
Based on its distance, brightness and estimated surface reflectivity, researchers estimate it is between about 600 and 1,500 kilometres across. Icy bodies this large are expected to be round, but that roundness still needs to be confirmed by follow-up observations.
Why was it not found before?
It lies in a dense Milky Way starfield, where the light of countless stars masked the faint moving object from earlier searches. Rubin's large mirror and wide field of view, combined with software that linked new observations to archival sightings back to 2016, made the identification possible.
What would make it an official dwarf planet?
Under the International Astronomical Union's definition, a dwarf planet must orbit the Sun, be massive enough for its gravity to shape it into a near-spherical form, and not have cleared its orbital neighbourhood. Follow-up measurements of 2026 ED138's size and shape will determine whether it meets that test.
Sources
- GeekWire, "Rubin Observatory finds its first dwarf planet candidate," 27 October 2026.
- Scientific American, "The Vera C. Rubin Observatory may have just discovered our solar system's sixth dwarf planet," 27 October 2026.
- Particle News, "Harvard Astronomers Uncover Large Trans-Neptunian Object, 2026 ED138," 27 October 2026.
- Avi Loeb, "Discovery of a Dwarf Planet Candidate in the Outer Solar System by the NSF-DOE Rubin Observatory," October 2026.
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