The object, 2026 ED138, could be one of the largest bodies known in the outer solar system, but its size and status still need confirming.
The NSF–DOE Vera C. Rubin Observatory has found its first candidate dwarf planet: an icy body orbiting the Sun beyond Neptune, currently about 46 times farther from the Sun than Earth is. The object, provisionally designated 2026 ED138, was announced on October 27 by the observatory and the International Astronomical Union’s Minor Planet Center.
Its exact size is still unknown. If the upper end of current estimates holds, it would rank among the largest bodies discovered beyond Neptune, and its discoverers say it is probably big enough to have pulled itself into a round shape, the key physical test for dwarf planet status.
How the object was found
Matthew Holman, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, spotted the object on October 13 while running Rubin data gathered earlier in the year through software he built with colleague Kevin Napier to link detections of moving objects. “My first reaction was one of excited disbelief,” Holman said in the observatory’s announcement.
Mario Jurić from the University of Washington, serving as Rubin’s Solar System lead scientist, subsequently scanned the observatory’s archives and photographs for additional detections. Altogether, the Simonyi Survey Telescope located in Chile captured the entity thirty times across twenty distinct nights spanning from March 4 through July 11, 2026. Historical photographs sourced from the Dark Energy Camera on the Víctor M. Blanco telescope, likewise situated in Chile, stretch the observational timeline back to 2016, yielding a trajectory exceeding a decade. The Minor Planet Center circular details both collections of sightings along with a provisional orbital path.
The object was not hiding because it is faint. It sits far in the southern sky and close to the plane of the Milky Way, where dense star fields make moving points hard to pick out. Holman told CNN that this location rules out many northern telescopes and that astronomers rarely search the Milky Way for such objects.
What is known about its size and orbit
Direct measurement of the object’s diameter remains beyond the reach of astronomers today. Instead, experts calculate this figure based on its distance and luminosity, relying heavily on surface reflectivity—where darker terrain suggests a more massive object, while a luminous surface points to a compact size. Consequently, researchers have published a broad estimated span ranging between 600 and 1,500 kilometers.
In a preprint posted on arXiv, Holman, Napier, Jurić alongside their peers prefer reflectivities placing the body at approximately 610 to 970 kilometers across. Even the lower bound surpasses the roughly 450-kilometer threshold above which researchers anticipate an icy world will adopt a spherical shape. The study points out that just nine recognized trans-Neptunian objects, featuring Pluto, Eris, Makemake and Haumea, outshine it intrinsically. Slight discrepancies exist between the brightness metrics reported by the team and the Minor Planet Center, a variance that subsequent tracking is expected to clarify.
The orbit is better constrained. The object circles the Sun about every 281 years at an average distance of roughly 43 astronomical units (one AU is the Earth–Sun distance). It ranges from about 37 AU at its closest to about 49 AU at its farthest, on a path tilted around 24 degrees to the plane of the planets. That tilt places it among the so-called hot classical Kuiper Belt objects. The team suggests Neptune’s gravity pushed it onto this inclined orbit long ago.
The orbit lies near a 12:7 resonance with Neptune, the same one occupied by Haumea, but simulations have not settled whether the object is locked into it. The authors also argue it is not a fragment of Haumea, because its color is redder than that of Haumea’s known collisional family.
| Object | Approx. diameter | Average distance from Sun | Orbital period |
|---|---|---|---|
| 2026 ED138 (candidate) | 600–1,500 km (estimate) | ~43 AU | ~281 years |
| Pluto | 2,377 km | ~39 AU | ~248 years |
| Eris | ~2,400 km | ~68 AU | ~557 years |
| Haumea | ~1,740 km (equatorial) | ~43 AU | ~285 years |
| Makemake | ~1,430 km | 45.8 AU | ~305 years |
Sources: NASA (Pluto, Eris, Haumea, Makemake); Minor Planet Center MPEC 2026-U85 and Holman et al. preprint (2026 ED138). Diameter for 2026 ED138 depends on its unmeasured surface reflectivity.
Why the find matters
The discovery offers an early look at what Rubin can do. The observatory began its 10-year Legacy Survey of Space and Time in June 2026 and will repeatedly image the entire southern sky. Before the survey formally started, its Solar System team had already submitted more than 11,000 new asteroids to the Minor Planet Center, including about 380 objects beyond Neptune, according to the observatory.
The researchers calculate that roughly three additional objects of this brilliance probably still await detection beyond the plane of the Milky Way, noting that the actual count is likely greater because the densely packed area close to the galactic plane has never been explored to this depth.
Michele Bannister, a planetary astronomer at the University of Canterbury in New Zealand who was not involved in the discovery, called the object “scientifically really cool” in comments to CNN, citing both its location beyond Neptune and its large size.
What happens next
Confirming the object’s size and status will take more data. The researchers call for thermal infrared measurements, which can separate size from reflectivity, and for timing the object’s passage in front of background stars, an event called a stellar occultation. Spectra could reveal whether its surface holds water ice or frozen methane, and brightness changes over time could show whether it is round. Holman told CNN that pinning down the size could take a few months.
Much of the detailed analysis comes from a preprint that has not yet been peer reviewed. A separate preprint, on which Holman is a co-author, reports finding the object in archival images from NASA’s TESS satellite going back to 2019, independently supporting the calculated orbit.
The International Astronomical Union, which classifies such bodies, currently recognizes five dwarf planets: Ceres, Pluto, Eris, Haumea and Makemake. For now, 2026 ED138 remains a candidate.
