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 dimensions remain undetermined. Should the highest projections prove accurate, this object will count as one of the most massive entities ever found past Neptune, with researchers noting that it likely possesses sufficient mass to achieve a spherical form through its own gravity, which serves as the primary physical criterion for dwarf planet classification.
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 of the University of Washington, Rubin’s Solar System lead scientist, then searched the observatory’s catalogs and images for more sightings. In all, Rubin’s Simonyi Survey Telescope in Chile recorded the object 30 times on 20 nights between March 4 and July 11, 2026. Archival images from the Dark Energy Camera on the Víctor M. Blanco telescope, also in Chile, extend the record back to 2016, giving a track of more than 10 years. The Minor Planet Center circular lists both sets of observations and a preliminary orbit.
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 understood regarding its scale and orbit
Astronomers cannot yet measure the object’s diameter directly. They infer it from its brightness and distance, an estimate that hinges on how much sunlight the surface reflects: a dark surface implies a larger body, a bright one a smaller body. Hence the wide announced range of 600 to 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 is positioned close to a 12:7 orbital resonance with Neptune, mirroring the one shared by Haumea, although numerical simulations have yet to confirm whether the body is permanently captured. Additionally, the researchers contend that the object cannot be considered a piece of Haumea, given that its surface exhibits a redder hue than the members of Haumea’s recognized impact 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 authors estimate that about three more objects this bright likely remain undiscovered away from the Milky Way’s plane, and say the true number is probably higher, since the crowded region near the plane has never been searched this deeply.
Michele Bannister, a planetary astronomer at the University of Canterbury in New Zealand who remained independent of the research team, described the body to CNN as “scientifically really cool,” highlighting its substantial dimensions alongside its position past Neptune.
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 stems from a preprint awaiting peer review. Another separate study, featuring Holman as one of the co-authors, documents spotting the object within archival imagery from NASA’s TESS satellite dating back to 2019, thereby independently corroborating the computed 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.
