The outer solar system continues to reveal its mysteries through the observations of the Vera C. Rubin Observatory. Within months of initiating its decade-long survey, astronomers have identified a potential new dwarf planet in the Kuiper Belt. This discovery was announced at the American Astronomical Society’s Division of Planetary Sciences meeting in Spokane, Wash., highlighting the ongoing efforts to map the remote and frigid regions beyond Neptune.
The object, designated 2026 ED138, was first detected in Rubin Observatory data collected between March 4 and July 11, 2025. Astrophysicist Matt Holman of the Smithsonian Astronomical Observatory in Cambridge, Mass., identified the object through analysis of its motion in the observatory’s data on October 13, 2025. Situated approximately 47 times farther from Earth than the Sun, ED138’s brightness indicates it could span 600 to 1,500 kilometers in diameter—making it comparable in size to known dwarf planets such as Ceres and Makemake. Its spherical shape suggests it may qualify as a dwarf planet, though verification is pending.
Holman expressed both excitement and caution, emphasizing the need to confirm its classification. Follow-up observations using the Dark Energy Camera in Chile, originally captured in 2016, provided crucial validation. Amateur astronomer Sam Deen, based in Simi Valley, Calif., further traced historical references to ED138 in photographic plates from Palomar Observatory dating to 1954. These decades-spanning observations allowed researchers to refine the object’s orbital path, revealing a 280-year revolution period.
ED138’s slow movement across the sky, combined with its alignment against a dense field of Milky Way stars, explains why it remained undetected until now. By integrating data from multiple surveys over nearly 70 years, astronomers have significantly improved orbital precision. This enhanced understanding has enabled predictions of an occultation—where ED138 passes in front of a distant star—scheduled for Halloween 2026. Such events can yield detailed insights into an object’s size, shape, and potential moons or rings.
Deen likened the timing to “being a kid in a candy shop,” noting the rarity of immediate occultation predictions for newly discovered solar system objects. The team continues to scrutinize ED138’s characteristics, aiming to solidify its status as a dwarf planet and deepen knowledge of the Kuiper Belt’s elusive population.
