TL;DR
Astronomers identified 2026 ED138 in Vera C. Rubin Observatory data and matched it to images dating back to 1937. It orbits the Sun every 281.1 years, but its size—and whether it is round enough to qualify as a dwarf planet—has not been confirmed.
Astronomers have identified 2026 ED138, a distant solar system object that takes 281.1 years to orbit the Sun, and are investigating whether it is large enough to be a dwarf planet. The object was detected in data from Chile’s Vera C. Rubin Observatory and then found in older sky images, but its size has not yet been established.
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Matthew Holman, a senior astrophysicist at the Smithsonian Astrophysical Observatory, spotted the object while reviewing Rubin Observatory data with a custom computer program. Holman and colleague Kevin Napier had already identified more than 2,000 small, bright objects in the data. This one stood out because it appeared unusually large. They worked with Mario Jurić, the observatory’s solar system lead scientist, to check whether the detection was real.
The team matched the object to earlier images taken over the past decade, allowing them to refine its orbit. They also located it in photographic plates from 1937 held in the Harvard plate stacks. The object is about 46 times farther from the Sun than Earth is. Its orbit is tilted nearly 25 degrees relative to the plane of the major planets, a feature the report says may reflect gravitational interactions with Neptune.
Current estimates put 2026 ED138 somewhere between 370 and 930 miles across, a broad range that is not enough to settle its classification. Brightness alone cannot establish size: a smaller object with a highly reflective surface could look as bright as a larger, less reflective one. Researchers need additional measurements to determine whether it is sufficiently large to have become nearly round under its own gravity.
A Possible Addition to the Dwarf Planets
If follow-up measurements show that 2026 ED138 is large enough and nearly round, it could join the five dwarf planets currently recognized by astronomers: Ceres, Pluto, Eris, Makemake and Haumea. That would add a member to a small, scientifically useful category of worlds that orbit the Sun but have not cleared their orbital paths of comparable debris.
The finding also points to a population of distant objects that may remain difficult to detect. Some bodies travel on elongated orbits and spend much of their time far from the Sun, where they are faint. Holman told Smithsonian Magazine that the objects currently observed could be the “tip of the iceberg”, with many others still undiscovered. That possibility is a reason to map and study the distant solar system, not evidence that a particular number of further dwarf planets has been found.
Paul Byrne, a planetary scientist at Washington University in St. Louis who was not involved in the discovery, called it exciting and told National Geographic that it “heralds a new era of solar system and planetary science.” His comment reflects the potential of the discovery; ED138’s dwarf-planet status remains unresolved.
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How Dwarf Planet Status Is Determined
A dwarf planet must orbit the Sun and be nearly round, while lacking enough gravitational influence to clear its orbital neighborhood of similar-sized bodies. The distinction explains why Pluto was reclassified in 2006: it shares its region with icy objects in the Kuiper Belt. Roundness is linked to an object’s size and gravity, but astronomers have not yet measured ED138 precisely enough to confirm that it meets the criterion.
Finding the object in older records strengthens the case that it is a real body and gives researchers a longer observational arc for calculating its path. It does not, on its own, determine the object’s physical dimensions or establish its formal classification. The Rubin Observatory images cited in the report were captured between March and June 2026.
““We know that it’s real. Every time you look at the predicted location, there it is.””
— Matthew Holman, senior astrophysicist at the Smithsonian Astrophysical Observatory
Size and Shape Still Need Checking
The central unanswered question is whether 2026 ED138 is large enough to be nearly round. The current diameter estimate spans 370 to 930 miles, and brightness cannot narrow that range reliably without information about how reflective its surface is. The object is therefore a candidate, not a confirmed dwarf planet.
Researchers are considering two ways to improve the measurement. Infrared observations could detect heat emitted after the body is warmed by sunlight, helping astronomers estimate its size. Alternatively, they could observe it pass in front of a star; the duration of the resulting dip in starlight, together with the object’s speed, can help calculate its dimensions. The report says astronomers are working toward observations, including with the Atacama Large Millimeter/submillimeter Array, but does not provide a confirmed measurement or classification date.
Upcoming Observations Could Settle Its Size
Holman said 2026 ED138 is not especially easy to observe at present, but should become more accessible over the next few months. Astronomers plan to pursue follow-up observations that can constrain its size, through infrared measurements, a stellar occultation, or both. Those results will determine whether the evidence supports dwarf-planet status or whether the object remains a distant body of uncertain classification.
Until such measurements are reported, the established findings are its detection, its recovered appearances in older images and its calculated 281.1-year orbit. No final size determination or formal recognition as a dwarf planet has been announced in the source report.
Key Questions
What is 2026 ED138?
It is a distant object orbiting the Sun and a candidate dwarf planet. Astronomers identified it in Rubin Observatory data and matched it to earlier images, including a photographic plate from 1937.
How long does it take to orbit the Sun?
Its calculated orbital period is 281.1 years. The object is about 46 times farther from the Sun than Earth is, according to the report.
Has 2026 ED138 been confirmed as a dwarf planet?
No. Its size and shape have not been confirmed. Astronomers need to determine whether it is sufficiently large to be nearly round under its own gravity.
How will astronomers measure its size?
They can study its infrared heat emission or observe it pass in front of a star and measure how long it blocks the star’s light. The report says follow-up observations are being pursued, but gives no final measurement yet.
How many dwarf planets are currently recognized?
The source report lists five: Ceres, Pluto, Eris, Makemake and Haumea. ED138 has not been added to that group.
Source: smithsonianmag.com
