Astronomers Flag Dwarf Planet Candidate 2026 ED138, Traced Back Through 1937 Glass Plates
Astronomers have identified a dwarf planet candidate, designated 2026 ED138 (also referred to as ED138), orbiting the Sun at 46 times Earth's distance. Smithsonian Magazine reported the finding on 12 November 2026, and the object's orbit takes 281.1 years to complete.
Matthew Holman, a senior astrophysicist at the Smithsonian Astrophysical Observatory, spotted the object while sifting through data from the Vera C. Rubin Observatory in Chile. He worked with colleague Kevin Napier, who helped run a custom-built computer program. That program picked out more than 2,000 bright points corresponding to newly discovered small, distant solar system objects. The output was a catalogue of detections, and the candidate was one of the entries that emerged from it.
Mario Jurić, the Rubin solar system lead scientist, helped verify the candidate. Verification matters at this distance, because a single detection can easily be mistaken for an artefact, a background asteroid, or a transient, meaning a brief, short-lived flash in the image. Independent confirmation from the observatory's own solar system team moves the object from a list entry toward a tracked body.
The archive extends the record well beyond the Rubin data. The object appears in sky photographs from the past decade, and it also appears in photographic plates from 1937 stored in the Harvard plate stacks. Those glass plates, exposed nearly nine decades ago, give astronomers a second position measurement separated from modern images by almost ninety years. For a body on a 281-year orbit, that long baseline is what turns a short run of sightings into a usable orbital fit.
ED138 moves on a plane tilted nearly 25 degrees from the orbital plane of the main planets, known as the ecliptic. A large inclination at this distance makes such objects hard to catalogue. They spend most of their time far from the ecliptic, where survey coverage is thinner and their slow motion can hide in the noise. The 1937 plates and the past decade of imaging help bridge that gap, though the available facts do not yet establish a full orbit solution, and the classification remains provisional.
The broader context here is methodological. Much of the recent progress in outer solar system discovery depends less on new telescopes than on the processing pipeline behind them. That pipeline includes difference imaging (subtracting older images from new ones so that changes stand out), linking detections across nights and years, and filtering out false positives at a scale no person could review by hand. The bottleneck has shifted from collecting light to processing and validating data.
In my view, the most useful part of this story for working astronomers and data engineers is the archive. Glass plates from 1937 are not an obvious input to a 2026 discovery pipeline, yet they supplied the time baseline that a modern survey alone could not. Digitised historical imagery, when it is searchable and well calibrated, becomes a long-lived asset that improves with every new survey that can be linked to it.
Whether ED138 ultimately qualifies as a dwarf planet is a question the current candidate label leaves open. What the reporting establishes is narrower: a distant object with a 281.1-year period and a near-25-degree tilt, identified in Rubin-era data, confirmed by the observatory's solar system team, and traced back through nearly a century of photographic records. Follow-up observations will determine how far that orbit can be pinned down, and the same archive-plus-survey approach is likely to be applied to other faint objects in the outer solar system.
