A bright, distant world hiding in the crowded glow of the Milky Way could soon give Pluto some company. Designated 2026 ED138, the object is the first dwarf-planet candidate identified by the Vera C. Rubin Observatory and may be one of the largest bodies ever found beyond Neptune. The discovery could eventually add a sixth dwarf planet to the solar system, although ED138 still needs follow-up observations before astronomers can make that call.
Rubin’s preliminary measurements place ED138 roughly 46 astronomical units from the Sun—about 46 times the average Earth-Sun distance and farther out than Pluto’s typical distance. Its estimated diameter ranges from approximately 600 to 1,500 kilometers, a wide uncertainty caused largely by the object’s unknown reflectivity. If the larger estimates hold, ED138 would be more than half Pluto’s diameter and among the most substantial known trans-Neptunian objects. The official Rubin announcement says infrared observations will be needed to narrow down its size and test whether it truly qualifies as a dwarf planet.
The object was pulled from Rubin data on October 13 by Matthew Holman, a Rubin Operations team member and Center for Astrophysics | Harvard & Smithsonian contributor. Holman and colleague Kevin Napier developed software capable of comparing billions of detections to determine which points of light belong to the same moving object. After ED138 stood out as unusually bright for its distance, Rubin Solar System lead scientist Mario Jurić searched the observatory’s earlier images and found 20 additional detections.
Those observations came from 30 Rubin exposures collected across 20 nights between March 4 and July 11, 2026. Archival images from the Dark Energy Camera on the Victor M. Blanco 4-meter Telescope, located at Chile’s Cerro Tololo Inter-American Observatory, pushed the object’s recorded history back to 2016. Together, the observations provide more than a decade of orbital evidence and helped establish that ED138 follows a path tilted nearly 25 degrees from the solar system’s main plane.
That inclination may explain why ED138 escaped earlier surveys. The object lies near the Milky Way’s dense central region, where countless background stars can overwhelm the faint signatures of distant solar-system bodies. Rubin’s strength is its repeated, wide-field imaging: the observatory’s enormous camera continuously scans the southern sky, allowing software to distinguish genuine motion from the largely static background. The National Science Foundation describes the facility as designed for a decade-long time-lapse survey of the changing universe.
For now, “dwarf planet” remains a description of what ED138 might be, not an official status. Under the International Astronomical Union’s definition, a dwarf planet must orbit the Sun, be massive enough for gravity to make it approximately round, and not have cleared its orbital neighborhood. The IAU currently recognizes Pluto, Ceres, Eris, Haumea, and Makemake; ED138 would become the sixth if its physical size and shape meet that standard. More infrared data and continued tracking should determine whether this newly exposed world is a true member of Pluto’s small planetary class—or simply another unusually bright Kuiper Belt object.
