Object

2026 ED138

A dwarf-planet candidate found by the Rubin Observatory beyond Neptune and announced on 27 October 2026, an icy world that may be 600 to 1,500 km across.

At a glance

Status
Candidate, not yet confirmed[1]Its size and shape await infrared measurements
Size
600 to 1,500 km across[1]The spread depends on how reflective its surface is
Orbit
37 to 49 au, once every 281 years[2]Tilted 24.5°; a hot-classical trans-Neptunian object
Where it is now
46 au from the Sun, beyond Pluto[1]
Found by
Rubin Observatory, Chile[1]Matthew Holman, in Rubin's data, 13 October 2026

Timeline

  1. December 30, 1937
    Earliest image, found later[2]
    A photographic plate matched to the orbit after the discovery; the first observation in JPL's solution
  2. March 4, 2026
    First Rubin image[4]
    The telescope recorded it, but no one had yet picked it out; the Minor Planet Center counts this as the discovery observation
  3. October 13, 2026
    Recognised in the data[1]
    A search code linked 30 images from 20 nights, 4 March to 11 July, and Holman saw how large it must be
  4. October 27, 2026
    Announced[4]
    The Minor Planet Center's circular, two weeks after the find, with the observatory's release the same day

2026 ED138 is a dwarf-planet candidate in the Kuiper belt, announced on 27 October 2026 as the first such find of the Rubin Observatory.[1] Based on its distance, brightness and an estimated surface reflectivity, its discoverers put its size between 600 and 1,500 km, and icy bodies that large are expected to be round, which is the test a dwarf planet must pass.[1] If confirmed, it would join the five dwarf planets the International Astronomical Union recognises: Pluto, Ceres, Eris, Haumea and Makemake.[1] The guide What is a dwarf planet? explains why the confirmation takes time.

Hidden in a crowded sky

The object was found by Matthew Holman of the Center for Astrophysics, Harvard & Smithsonian, a member of the Rubin operations team.[1] On the evening of 13 October 2026 he was running data the observatory had collected earlier in the year through a search code built to compare billions of detections of moving objects and find the ones that belong together, and he immediately noticed that the brightness and distance of one of them meant it was unusually large.[1] Colleagues then found 20 more observations going back to 4 March 2026; in all, Rubin's Simonyi Survey Telescope had observed it 30 times on 20 nights between 4 March and 11 July.[1] Archival images from the Dark Energy Camera in Chile provided data back to 2016, which allowed the team to trace more than ten years of its orbit.[1] Once its orbit was known, astronomers looked back and found it on a photographic plate from 1937: JPL's orbit solution now starts with that observation, of 30 December 1937.[2]

It had escaped earlier surveys because it lies far south, in a region of sky close to the plane of the Milky Way that is crowded with millions of stars.[1][3] The discovery paper estimates that about three more objects as bright as it remain undiscovered away from the Galactic plane, and probably more within it, where no search has yet looked to this depth.[3]

Its orbit and size

2026 ED138 is currently about 46 astronomical units from the Sun; Pluto, for comparison, averages 40.[1] JPL's catalogue gives an orbit from 36.9 to 49 astronomical units, with a semi-major axis of 42.9 astronomical units, and the Minor Planet Center's circular gives a period of 281 years.[2][4] The orbit is tilted almost 25 degrees to the plane of the solar system, which makes it a hot-classical trans-Neptunian object.[1] The discovery paper notes that its orbit lies at the edge of the 12:7 resonance with Neptune, like that of the dwarf planet Haumea, but that its colour is too red for it to belong to Haumea's family of collision fragments.[3]

Its absolute magnitude, the brightness it would have at a standard distance, is 3.19 in the discovery paper and 2.85 in JPL's catalogue, which makes it one of the ten intrinsically brightest trans-Neptunian objects known.[3][2] Brightness alone does not give a size: the paper's range of 612 to 1,530 km spans surfaces that reflect anywhere from a quarter of the sunlight falling on them down to 4 per cent.[3] Observations in the infrared are needed to constrain its exact size and confirm its nature as a dwarf planet.[1] For scale, Pluto is about 2,377 km across.[5]

What is not yet known

Three things wait for further work. The first is its size, which the infrared measurement will settle.[1] The second is whether it is round, the condition for a dwarf planet under the definition the IAU adopted in 2006.[6] The third is a name: for now it carries only the provisional designation the Minor Planet Center assigned when it announced the observations.[4] This page will be updated as each is published.

Can I see it?

No. It is bright enough for professional spectroscopy from the ground and for detailed study with the Hubble and James Webb space telescopes, but far beyond the reach of any amateur instrument.[3]

Sources

  1. [1]NSF–DOE Vera C. Rubin Observatory, NSF–DOE Vera C. Rubin Observatory Reveals Its First Dwarf Planet Candidate in Our Solar System — rubinobservatory.org, retrieved November 5, 2026
  2. [2]NASA/JPL Small-Body Database, 2026 ED138 — ssd.jpl.nasa.gov, retrieved November 5, 2026
  3. [3]arXiv (submitted to The Astronomical Journal), 2026 ED138: A Large Trans-Neptunian Object in Early Rubin Observatory Data, and How Many More May Remain — doi.org, retrieved November 5, 2026
  4. [4]IAU Minor Planet Center, MPEC 2026-U85: 2026 ED138 — minorplanetcenter.net, retrieved November 5, 2026
  5. [5]NASA, Pluto: Facts — science.nasa.gov, retrieved November 5, 2026
  6. [6]NASA, Pluto & Dwarf Planets — science.nasa.gov, retrieved November 5, 2026

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