Rubin Observatory Finds Potential New Dwarf Planet Beyond Pluto

A trans-Neptunian object designated 2026 ED138 has been identified by researchers analyzing data from the Simonyi Survey Telescope at the Vera C. Rubin Observatory. The icy body, estimated to be between 600 and 1,500 kilometres in diameter, orbits at roughly 46 astronomical units, placing it beyond Pluto and making it a candidate for dwarf-planet status.

The discovery was announced at a press briefing by senior astrophysicist Matthew Holman of the Harvard & Smithsonian Center for Astrophysics and University of Washington astronomer Mario Jurić, who leads Rubin’s solar-system team. Holman initially detected the object using a custom search algorithm, while Jurić added further observations that extend the object's recorded trajectory back to March 2026 and, through archival images, to 2016.

"If confirmed as a dwarf planet, ED138 would join a very small family of worlds," Holman said. "Rubin will image the whole southern sky again and again for 10 years, so any others hiding in the places earlier surveys skipped are now within reach."

"Finding an object this big, roughly 1,000 kilometres across, is something that happens maybe once in a generation," Jurić added. "It's the largest trans-Neptunian object found in about 20 years, and Rubin turned it up while we were still commissioning the telescope."

The team used Rubin’s continuous sky-monitoring capability and advanced data-processing techniques to isolate the moving object amid the dense star fields of the Milky Way’s plane. Their analysis suggests the object's size and brightness are consistent with a roughly spherical shape, a key criterion for dwarf-planet classification, though precise measurements are still required.

The finding adds to a growing catalog of distant solar-system bodies uncovered by Rubin since early data collection began in 2026. Earlier in the year, the observatory’s solar-system program reported more than 11,000 new asteroids and about 380 new trans-Neptunian objects, describing the results as “the tip of the iceberg.”

"Rubin is giving us an unprecedented capacity to explore the sky through a combination of speed, depth, and precision," Jurić said. "And the discovery is just the beginning: once we identify a new object, we can search back months, and sometimes even decades, finding it in images where nobody knew to look. This ability to both discover and 'precover' objects is transforming how quickly and accurately we can determine their orbits and understand the distant solar system."

The Vera C. Rubin Observatory is funded by the U.S. National Science Foundation and the U.S. Department of Energy’s Office of Science.