Rubin Observatory Discovers Distant Dwarf Planet Candidate 2026 ED138
Spotted in commissioning data and traced back a decade, the icy trans-Neptunian object could become the first dwarf planet added to the official list since 2008.
In short
- Astronomers identified 2026 ED138, a trans-Neptunian object estimated between 600 and 1,500 kilometers across, making it the largest found in roughly 20 years.
- The candidate was discovered on October 13, 2026, using search algorithms applied to data from the Simonyi Survey Telescope in Chile.
- Archival imaging from the Dark Energy Camera traced the object's tilted orbit back to 2016 through precovery techniques.
- Confirmation of dwarf planet status requires follow-up infrared observations and stellar occultation measurements to verify hydrostatic equilibrium.
Astronomers analyzing data from the NSF–DOE Vera C. Rubin Observatory announced on October 27, 2026, the discovery of a large trans-Neptunian object designated 2026 ED138, identifying it as a major dwarf planet candidate. Discovered during the commissioning period leading up to the survey facility's primary mission, the object orbits in the outer reaches of the solar system beyond Pluto. If confirmed by the International Astronomical Union (IAU), 2026 ED138 would represent the first addition to the recognized family of dwarf planets since 2008, joining Ceres, Pluto, Eris, Haumea, and Makemake.
The findings were presented at a press conference during the 58th Annual Division for Planetary Sciences meeting of the American Astronomical Society in Spokane, Washington, by discovery lead Matthew Holman of the Center for Astrophysics | Harvard & Smithsonian and Mario Jurić of the University of Washington, according to announcements by the Vera C. Rubin Observatory and the International Astronomical Union Minor Planet Center.
Uncovering 2026 ED138 in the Dense Milky Way
Matthew Holman identified the candidate on the evening of October 13, 2026, while running data collected earlier in the year through specialized search software developed alongside colleague Kevin Napier. The tracking code evaluates billions of moving object detections to link observations belonging to the same body. Holman immediately noted that the object's high apparent brightness and distance pointed to an unusually large diameter.
Despite its brightness, 2026 ED138 evaded detection by earlier surveys because it sits in a portion of the sky crossing the plane of the Milky Way. In this region, millions of crowded background stars routinely obscure faint and moving objects. Rubin Observatory's wide-field Simonyi Survey Telescope, equipped with an eight-meter mirror and the largest digital camera ever built, enabled the team to distinguish the moving body within the stellar background, as detailed by GBH News.
Orbit, Size, and Characteristics of the Dwarf Planet Candidate
The candidate currently sits at a distance of approximately 46 astronomical units (AU) from the Sun, where 1 AU represents the average distance between Earth and the Sun. For comparison, dwarf planet Pluto maintains an average orbital distance of roughly 40 AU, according to reporting from Phys.org.
Based on its observed brightness, distance, and assumed surface reflectivity (albedo), researchers estimate the diameter of 2026 ED138 to be between 600 and 1,500 kilometers (roughly 370 to 930 miles), centering near 1,000 kilometers across. Under established planetary science principles, icy bodies of this magnitude typically possess sufficient self-gravity to pull themselves into hydrostatic equilibrium, achieving a rounded shape.
The orbital pathway of 2026 ED138 is inclined nearly 25 degrees relative to the ecliptic plane of the solar system. This steep tilt classifies it as a "hot-classical" trans-Neptunian object. Astronomers suspect the world originally formed closer to the Sun before gravitational interactions with Neptune scattered it outward billions of years ago into its present trajectory, as reported by GeekWire.
A Decade of Archival Precovery Data
Following Holman's initial detection on October 13, Jurić searched Rubin Observatory's internal image logs and uncovered 20 additional observations spanning back to March 4, 2026. In total, the Simonyi Survey Telescope recorded the candidate 30 times across 20 distinct nights between March 4 and July 11, 2026.
To establish a precise orbital track, astronomers turned to external records through the Asteroid Institute's ADAM Precovery service. The platform searched through archival exposures captured by the Department of Energy-fabricated Dark Energy Camera (DECam), which operates on the Victor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile. The query yielded historical sightings dating back to 2016, enabling the research team to map more than a decade of the candidate's orbital path.
Jurić noted that identifying a trans-Neptunian object of this scale happens perhaps once in a generation, representing the largest such body discovered in approximately two decades, according to GeekWire.
Path to Confirmation and Public Data Access
While 2026 ED138 stands as a strong candidate, official recognition as a dwarf planet depends on formal evaluation. Under criteria established in 2006 by the IAU, a dwarf planet must orbit the Sun and possess sufficient mass for self-gravity to overcome rigid body forces into hydrostatic equilibrium, without having cleared its orbital neighborhood. The official list of dwarf planets has not changed since 2008.
Confirming the physical nature of 2026 ED138 will require follow-up measurements. Thermal observations in the infrared spectrum are planned to disentangle the object's exact diameter from its surface reflectivity. In addition, astronomers plan to observe stellar occultations—events where the body passes directly in front of background stars—to measure its precise outline and confirm whether it is round, as Jurić explained to GeekWire.
Rubin Observatory is jointly funded by the National Science Foundation and the U.S. Department of Energy's Office of Science, with international operational contributions from institutions including France's CNRS/IN2P3. Ahead of its primary 10-year Legacy Survey of Space and Time (LSST), which formally commenced in June 2026, the team submitted observations of over 11,000 new asteroids and approximately 380 trans-Neptunian objects to the Minor Planet Center in April 2026, as noted by the National Science Foundation.
Images and raw observational records of 2026 ED138 are accessible to institutional researchers via the web-based Rubin Science Platform. Public audiences and educators can examine the candidate's three-dimensional trajectory through the interactive web application Orbitviewer.
Questions people ask
What is 2026 ED138?
2026 ED138 is a large trans-Neptunian object discovered in 2026 by the Vera C. Rubin Observatory. With an estimated diameter of 600 to 1,500 kilometers, it is considered a candidate dwarf planet.
How far away is 2026 ED138?
The object is currently located about 46 astronomical units (AU) from the Sun, farther than Pluto's average distance of 40 AU.
Why was 2026 ED138 not discovered earlier?
The object's orbital path crosses against the dense background of the Milky Way galaxy, where millions of crowded stars visually masked the moving body from previous survey instruments.
What is needed to confirm its status as an official dwarf planet?
Astronomers need infrared thermal measurements to pin down its exact size and reflectivity, as well as stellar occultation data to confirm that its gravitational mass has pulled it into a rounded shape.
Sources
- Rubin Observatory reveals its first dwarf planet candidate in our solar systemPhys.org, Oct 27, 2026
- NSF–DOE Vera C. Rubin Observatory Reveals Its First Dwarf Planet Candidate in Our Solar Systemrubinobservatory.org, Oct 27, 2026
- New dwarf planet candidate discovered by NSF–DOE Rubin ObservatoryNational Science Foundation, Oct 27, 2026
- A new pal for Pluto? Rubin Observatory finds its first dwarf planet candidategeekwire.com, Oct 27, 2026
- Move over, Pluto: Telescope spots dwarf planet prospectCosmic Log, Oct 28, 2026
- Potential new dwarf planet found by Harvard astrophysicistsGBH, Oct 27, 2026
- NSF–DOE Vera C. Rubin Observatory reveals its first dwarf planet candidate in our solar systemSLAC National Accelerator Laboratory
How this story was made: the newsroom picked it up from phys.org, Google News and Reddit, gathered the full text of the sources above, and drafted it with AI assistance. Every factual claim was then checked against those sources before publishing (39 claims checked). Illustrations marked as AI-generated are not photographs. Spotted an error? Tell us.
Published October 28, 2026 at 06:44 UTC
