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, 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 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 concealing itself due to any dimness. Positioned deep within the southern heavens and near the galactic plane, crowded star fields render shifting dots difficult to discern. Holman mentioned to CNN that this positioning disqualifies numerous northern observatories and that researchers seldom scan the Milky Way for bodies of this nature.
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 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 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
Additional data is required to verify the dimensions and nature of the object. Investigators advocate for thermal infrared observations—capable of distinguishing scale from albedo—alongside tracking the body as it transits background stars, a phenomenon known as stellar occultation. Analyses of the spectrum might indicate the presence of water ice or solid methane on its exterior, whereas fluctuations in luminosity over time could determine its sphericity. Holman mentioned to CNN that establishing the exact measurements might require a couple of 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.
