The Vera C. Rubin Observatory, jointly funded by the U.S. National Science Foundation (NSF) and U.S. Department of Energy (DOE), identified a distant object that may qualify as a dwarf planet, pending infrared observations.
The observatory said the International Astronomical Union’s (IAU) Minor Planet Center announced the provisional designation 2026 ED138 on Oct. 27. Matthew Holman, a senior astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, identified the object Oct. 13 while analyzing Rubin observations collected earlier in 2026.
Across the March 4 to July 11 survey window, ED138 appeared in 30 observations distributed over 20 nights. Earlier images from the Dark Energy Camera let researchers trace its recorded path back to 2016.
Rubin puts ED138 about 46 astronomical units (AU) from the Sun now. Pluto’s average distance is about 40 AU. The observatory estimates ED138’s diameter at 600 to 1,500 kilometers, using its brightness and an estimate of how much sunlight its surface reflects. Infrared observations are needed to narrow the range, Rubin said.
The observatory classifies ED138 as a hot-classical trans-Neptunian object. Its orbit is inclined nearly 25 degrees to the solar system’s plane, and gravitational interactions with Neptune may have altered its original path.
ED138 was found in a crowded field near the plane of the Milky Way, where background stars may have made it difficult for earlier surveys to detect. Rubin said repeated sky scans and software that searches for moving objects helped researchers identify its motion.
The IAU’s 2006 definition requires a dwarf planet to orbit the Sun and be nearly round because of its own gravity. It also must not be a satellite or have “cleared the neighborhood” around its orbit. Rubin says ED138’s size could make it nearly round, but its status is unconfirmed until follow-up observations refine the estimate. The findings add size details to an earlier EconoTimes report on ED138’s discovery and designation.
