A giant icy world orbiting beyond Pluto has been discovered by astronomers using the Vera C. Rubin Observatory, and if confirmed as a dwarf planet, it could become the sixth officially recognized dwarf planet in our solar system. The object, temporarily named 2026 ED138, was first spotted in October by Harvard & Smithsonian Center for Astrophysics senior astrophysicist Matthew Holman, who analysed earlier 2026 observations from the Simonyi Survey Telescope. The finding, announced at a press conference, adds to a growing collection of discoveries from the observatory's early operations.
The breakthrough came on the evening of October 13, when Holman examined observations gathered by Rubin earlier in 2026, using specialised software he developed with his colleague Kevin Napier. The program compares billions of telescope detections to find points of light that appear in multiple observations and move as a single object. When it flagged ED138, Holman realised its brightness and distance suggested an unusually large body.
Matthew Holman, senior astrophysicist at the Harvard & Smithsonian Center for Astrophysics, described his first reaction as one of "excited disbelief." He said he immediately began checking whether he or the code had made a mistake. Mario Jurić, a University of Washington astronomy professor who leads Rubin's solar system team, then examined Rubin's stored observations and located 20 additional detections of ED138, including some captured as early as March 2026. The team also found images of the object dating back to 2016 in historical records from other surveys, allowing them to reconstruct more than a decade of its orbital motion.
ED138 currently lies about 46 astronomical units (au) from the Sun, where one au is the average Earth–Sun distance. For comparison, Pluto's average orbital distance is about 40 au. Because it travels beyond Neptune, astronomers classify it as a trans-Neptunian object (TNO). To qualify as a dwarf planet, an object's gravity must be strong enough to pull it into a nearly round shape. Using brightness, distance and reflectivity estimates, astronomers calculate ED138 could be between 600 and 1,500 kilometres across -- within the range where an icy body would typically become round. More observations are needed to determine its actual dimensions.
Jurić said: "Finding an object this big, roughly 1,000 kilometres across, is something that happens maybe once in a generation. It's the largest trans-Neptunian object found in about 20 years, and Rubin turned it up while we were still commissioning the telescope."
One reason ED138 avoided detection for so long is its location near the plane of the Milky Way, where millions of stars create a crowded background that masks the faint movement of distant objects. Rubin's advantage is its ability to image the southern sky repeatedly and use advanced algorithms to sift through billions of light detections for subtle changes.
Holman noted: "If confirmed as a dwarf planet, ED138 would join a very small family of worlds. Rubin will image the whole southern sky again and again for 10 years, so any others hiding in the places earlier surveys skipped are now within reach."
If confirmed, ED138 would join the five dwarf planets currently recognised by the International Astronomical Union: Pluto, Ceres, Eris, Haumea and Makemake. Rubin's solar system researchers had already reported more than 11,000 previously unknown asteroids and about 380 new TNOs before the Legacy Survey of Space and Time (LSST) officially began in June 2026. The team described those finds as "the tip of the iceberg."
Analysis
Why This Matters
- If 2026 ED138 is confirmed as a dwarf planet, it would become only the sixth such body officially recognised, reshaping the map of our solar system's outer reaches and adding to the handful of large worlds beyond Neptune.
- The discovery demonstrates the Vera C. Rubin Observatory's power to find objects that earlier surveys missed, especially in crowded star fields, suggesting many more hidden worlds may soon be uncovered.
- Understanding the population of large trans-Neptunian objects helps scientists refine models of how the solar system formed and how giant planets migrated early in its history.
Background
The outer solar system beyond Neptune contains thousands of icy bodies, but only a handful are large enough to be considered dwarf planets. The International Astronomical Union defines a dwarf planet as a body that orbits the Sun, has enough gravity to become round, has not cleared its orbital neighbourhood, and is not a moon. Pluto was reclassified from planet to dwarf planet in 2006, sparking ongoing debate. The Rubin Observatory, a new facility in Chile, is conducting a 10-year survey of the southern sky that is expected to dramatically increase the known number of small solar system bodies.
What to Watch
- The International Astronomical Union will need to receive and evaluate formal evidence about ED138's size and shape before any official classification.
- Follow-up observations from telescopes like Hubble or the James Webb Space Telescope could provide more precise size and albedo measurements.
- Rubin's ongoing LSST survey is likely to identify additional large TNOs, potentially including other objects that could qualify as dwarf planets.
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11 claims in this story checked against 1 source: 11 supported.
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- SupportedA giant icy world beyond Pluto has been discovered.Latest Science News -- ScienceDaily: “An enormous icy world discovered beyond Pluto could soon become the sixth officially recognized dwarf planet in our solar system.”
- SupportedIf confirmed as a dwarf planet, 2026 ED138 could become the sixth officially recognized dwarf planet.Latest Science News -- ScienceDaily: “If its status is confirmed, it would join the five dwarf planets currently recognized by the International Astronomical Union: Pluto, Ceres, Eris, Haumea and Makemake.”
- SupportedED138 is estimated to be among the largest dwarf planet candidates found beyond Neptune.Latest Science News -- ScienceDaily: “Early estimates suggest it ranks among the largest dwarf planet candidates ever found beyond Neptune.”
- SupportedED138 was spotted near the crowded plane of the Milky Way.Latest Science News -- ScienceDaily: “ED138 occupies a region of the sky near the plane of the Milky Way, where millions of stars create an exceptionally crowded background.”
- SupportedHolman made the initial discovery on the evening of October 13 by examining Rubin observations gathered earlier in 2026.Latest Science News -- ScienceDaily: “The breakthrough occurred on the evening of October 13, when Holman examined observations gathered by Rubin earlier in 2026.”
- SupportedHolman said his first reaction was “excited disbelief.”Latest Science News -- ScienceDaily: ““My first reaction was one of excited disbelief,” Holman said.”
- SupportedJurić found 20 additional detections, including some from March 2026, and the team found images dating back to 2016.Latest Science News -- ScienceDaily: “Jurić examined Rubin's stored observations and located 20 additional detections of ED138, including some captured as early as March 2026. The researchers then searched historical records from other astronomical surveys and identified images of the object dating back to 2016.”
- SupportedED138 is about 46 astronomical units from the Sun, while Pluto's average orbital distance is about 40 au.Latest Science News -- ScienceDaily: “ED138 currently lies approximately 46 astronomical units (au) from the Sun. One astronomical unit represents the average distance separating Earth and the Sun. By comparison, Pluto's average orbital distance is about 40 au.”
- SupportedAstronomers estimate ED138 could be 600 to 1,500 kilometres across, but more observations are needed to establish its actual dimensions.Latest Science News -- ScienceDaily: “astronomers calculate that it could measure anywhere from 600 to 1,500 kilometers across. [...] scientists will need more observations to establish ED138's actual dimensions”
- SupportedJurić said an object roughly 1,000 kilometres across is found perhaps once in a generation and called it the largest trans-Neptunian object found in about 20 years.Latest Science News -- ScienceDaily: ““Finding an object this big, roughly 1,000 kilometers across, is something that happens maybe once in a generation,” Jurić said. “It's the largest trans-Neptunian object found in about 20 years, and Rubin turned it up while we were still commissioning the telescope.””
- SupportedBefore LSST officially began in June 2026, Rubin researchers had reported more than 11,000 previously unknown asteroids and about 380 new TNOs.Latest Science News -- ScienceDaily: “In April, Rubin's solar system researchers reported observations of more than 11,000 previously unknown asteroids, including approximately 380 new trans-Neptunian objects. [...] LSST, which officially started in June 2026.”
