Vera Rubin Observatory discovers potential dwarf planet 2026 ED138 beyond Neptune

Astronomers have identified a potential new dwarf planet designated 2026 ED138, located approximately 46 astronomical units from the Sun—beyond Neptune's orbit. The discovery was made by Matthew Holman, a senior astrophysicist at Harvard & Smithsonian's Center for Astrophysics and a member of the Vera C. Rubin Observatory operations team, who was analyzing observational data collected during the telescope's early operations in 2026.

Holman detected the object on October 13 while running archived data through a search algorithm he developed with colleague Kevin Napier. The algorithm scans billions of moving object detections to identify those corresponding to the same celestial body. Upon discovery, Holman noted his "first reaction was one of excited disbelief," prompting immediate verification checks. Working with Mario Jurić, the Rubin Observatory's Solar System Lead Scientist at the University of Washington, the team confirmed the discovery by locating 20 additional observations in Rubin's catalog dating back to March 2026. Using archival data from the Dark Energy Camera at Cerro Tololo Inter-American Observatory, researchers traced the object's orbital history back to 2016, providing approximately a decade of observational evidence.

ED138 is estimated to measure between 600 and 1,500 kilometers (370–930 miles) in diameter, making it potentially larger than Ceres, the smallest of the five officially recognized dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris. The object's size suggests it may be massive enough for gravity to have shaped it into a spherical form—a key criterion for dwarf planet classification under International Astronomical Union standards. As a trans-Neptunian object, ED138 orbits beyond Neptune in a region known as the Kuiper Belt. Its orbital plane is tilted approximately 25 degrees relative to the solar system's plane, suggesting past gravitational interaction with Neptune.

The discovery was announced on October 27 through a Minor Planet Electronic Circular and presented at a press conference during the 58th Annual Division for Planetary Sciences meeting in Spokane, Washington. Holman cautioned that ED138 remains a candidate pending confirmation: determining its official dwarf planet status requires measuring its reflectivity and physical size through infrared observations, work expected to take several months. The discovery was made possible partly because ED138's location in the southern sky and its position near the Milky Way plane made it difficult to detect with northern-hemisphere telescopes or standard sky surveys.

The Vera C. Rubin Observatory, located atop Cerro Pachón in Chile and jointly funded by the U.S. National Science Foundation and Department of Energy, houses the world's largest digital camera (3.2 gigapixels) and achieved first light in April 2025. The facility began its decade-long Legacy Survey of Space and Time in June 2026, imaging the entire southern sky every few days. Scientists anticipate that Rubin will discover approximately 32,000 additional objects beyond Neptune's orbit over the next decade, including potentially several more dwarf planets.