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, identified the body on October 13 while processing Rubin observations collected earlier that year using a program he developed alongside associate Kevin Napier to connect sightings of shifting objects. “My initial reaction was a mix of thrilled disbelief,” Holman remarked 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 known about its size 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 and their colleagues favor reflectivities that would put the object at roughly 610 to 970 kilometers wide. Even the low end exceeds the size of about 450 kilometers above which the team expects an icy body to be round. The paper notes that only nine known trans-Neptunian objects, including Pluto, Eris, Makemake and Haumea, are intrinsically brighter. The team and the Minor Planet Center report slightly different brightness values, a gap that further observations should resolve.
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 glimpse into Rubin’s capabilities. The observatory launched its decade-long Legacy Survey of Space and Time in June 2026, designed to continuously photograph the whole southern sky. Prior to the official launch of the survey, the institution’s Solar System group had already reported upwards of 11,000 fresh asteroids to the Minor Planet Center, encompassing roughly 380 trans-Neptunian bodies, as noted by the facility.
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.