A possible dwarf planet has been hiding beyond Pluto against one of the worst backdrops imaginable for a cosmic search: the densely packed stars of the Milky Way. The Vera C. Rubin Observatory identified the object now called 2026 ED138 by detecting its tiny movement through that crowded field.
The discovery, announced October 27, is substantial but not finished. Rubin scientists estimate that ED138 is somewhere between 600 and 1,500 kilometers wide and currently about 46 astronomical units from the Sun. That could place it among the largest dwarf-planet candidates known beyond Neptune—but infrared observations are still needed to pin down its size and determine whether it officially belongs in the Solar System’s small family of recognized dwarf planets.
The discovery began with excited disbelief
According to the Rubin Observatory’s official account, operations team member Matthew Holman found ED138 on October 13 while running observations through search code developed with Kevin Napier of the Center for Astrophysics | Harvard & Smithsonian. The software compares enormous numbers of detections and looks for points of light that belong to the same moving object.
The brightness and apparent distance immediately looked unusual. Holman’s first task was not naming a new world but checking whether the result was an error. Other team members searched Rubin’s data and found 20 additional observations. In total, the observatory had photographed ED138 30 times on 20 nights between March 4 and July 11, 2026.
That sequence is the visual payoff. In Rubin’s discovery mosaic, ED138 is not a dramatic globe with mountains or clouds. It is a faint speck changing position among thousands of stars. The movement, rather than a close-up portrait, is what tells astronomers they are looking at a nearby Solar System body instead of another distant star.
A ten-year trail was waiting in old images
Once scientists knew where to look, the object acquired a history. The Asteroid Institute’s ADAM Precovery service found ED138 in archival images from the Dark Energy Camera, extending the observation record back to 2016. A newly recognized object therefore came with more than a decade of hidden evidence.
Astronomers call this kind of archival recovery “precovery.” Earlier photographs were not taken because anyone knew ED138 existed; the object simply happened to be in them. Finding those older appearances gives researchers a much longer section of its orbit and improves their ability to calculate where it has been and where it is going.
That reversal is one of Rubin’s most satisfying tricks. The telescope discovers a moving point today, and suddenly yesterday’s images become evidence. A world can be new to science without being new to the camera.
Why it is still a candidate
The National Science Foundation describes ED138 as a possible dwarf planet, not a confirmed sixth member of the official list. The International Astronomical Union currently recognizes Pluto, Ceres, Eris, Haumea and Makemake.
Being beyond Neptune is not enough. A dwarf planet must have enough mass for its own gravity to pull it into a rounded shape, while not clearing other objects from its orbital neighborhood. Scientists do not yet have a resolved photograph of ED138’s surface or a precise measurement of its diameter. Their 600-to-1,500-kilometer estimate comes from its brightness, distance and assumptions about how reflective its surface may be.
Icy bodies within that range are expected to become round, which is why the designation is scientifically reasonable. The range is also enormous. At its lower end, ED138 would be smaller than Ceres; at its upper end, it would be larger than several established dwarf planets. Infrared measurements can help separate a smaller bright surface from a larger dark one and tell researchers which end of the estimate is closer to reality.
The Milky Way helped hide it
ED138 sits near the plane of the Milky Way, where the sky is cluttered with millions of background stars. To an ordinary survey, its faint appearance can vanish into that celestial crowd. Rubin’s advantage is repetition: it returns to the southern sky again and again, producing the changing images that algorithms can compare.
The object’s orbit adds another clue to its history. It is tilted nearly 25 degrees from the main plane of the Solar System, placing it among so-called hot-classical trans-Neptunian objects. “Hot” describes the population’s dynamically stirred orbits rather than their temperature. Researchers think gravitational encounters with Neptune may have disturbed ED138 from an earlier path.
The observatory’s official release and animations show that tilted route in three dimensions. The video is an orbital reconstruction based on measured data, not footage of a visible planet moving through space.
Rubin has only started repeating the sky
Rubin began its decade-long Legacy Survey of Space and Time in June 2026. Even before formal survey operations, its team submitted observations of more than 11,000 new asteroids, including roughly 380 trans-Neptunian objects, to the Minor Planet Center.
ED138 is different from a giant asteroid count because its possible size and roundness could put it in a much smaller club. It also demonstrates how the survey’s scale works: wide images find the crowded field, repeated visits reveal movement, and archival searches turn a fresh detection into a ten-year orbital record.
The honest ending is not that the Solar System definitely has a newly recognized dwarf planet. It is that astronomers have found an unusually large candidate in a place previous surveys struggled to search, and the evidence is strong enough to organize follow-up observations around the world. ED138 spent years masquerading as one more light in the Milky Way. Now science knows exactly where to look.
Featured image: Mosaic of 2026 ED138 observations. Credit: NSF–DOE Vera C. Rubin Observatory/NOIRLab/SLAC/AURA; image processing by M. Jurić, D. de Martin and M. Zamani. Used unchanged under CC BY 4.0 via NOIRLab.
