Astronomers have identified a massive icy world beyond Pluto that could become the sixth dwarf planet. The object, temporarily designated 2026 ED138, was detected by the NSF-DOE Vera C. Rubin Observatory. If the International Astronomical Union confirms its status, it would join Pluto, Ceres, Eris, Haumea, and Makemake as the only recognized dwarf planets in our solar system.
Discovery at the Vera C. Rubin Observatory
Matthew Holman, a senior astrophysicist at the Harvard & Smithsonian Center for Astrophysics, made the initial detection on the evening of October 13. He was reviewing data gathered earlier in 2026 using specialized software developed with colleague Kevin Napier. The program scans billions of telescope detections to find points of light that move in ways consistent with solar system bodies.
Holman noted that the object’s apparent brightness and extreme distance suggested something unusually large. “My first reaction was one of excited disbelief,” Holman said. “Objects like this are very rare, so I immediately started checking whether I or the code had done something wrong.”
Mario Juri, an astronomy professor at the University of Washington who leads the Rubin solar system team, helped verify the finding. He located 20 additional detections of the object in Rubin’s archives, including images from March 2026. The team also found historical records of the object dating back to 2016. This decade-long trail of observations allowed researchers to reconstruct its orbital motion and confirm the discovery.
Size and Classification as a Dwarf Planet Candidate
2026 ED138 currently sits about 46 astronomical units from the Sun. One astronomical unit is the average distance between Earth and the Sun. Pluto orbits at an average distance of roughly 40 astronomical units. Because it travels beyond Neptune, scientists classify it as a trans-Neptunian object.
Estimates suggest the world measures between 600 and 1,500 kilometers across. An object of this size, composed primarily of ice, would likely have enough gravity to pull itself into a nearly round shape. This roundness is a key requirement for dwarf planet status. However, scientists need more precise measurements to confirm its exact dimensions and final classification.
“Finding an object this big, roughly 1,000 kilometers across, is something that happens maybe once in a generation,” Juri said. “It’s the largest trans-Neptunian object found in about 20 years, and Rubin turned it up while we were still commissioning the telescope.”
Why It Was Hidden for So Long
The object remained undetected for years because it lies near the plane of the Milky Way. This region contains millions of stars, creating a dense background that makes faint, distant objects difficult to spot. Earlier surveys often missed objects in this crowded field of view.
The Vera C. Rubin Observatory has a distinct advantage. It repeatedly images the southern sky and uses advanced algorithms to track subtle shifts in object positions. This capability allows it to distinguish moving solar system bodies from stationary stars. The observatory began its Legacy Survey of Space and Time in June 2026, but even during commissioning, it has already identified thousands of new asteroids and trans-Neptunian objects.
“Rubin is giving us an unprecedented capacity to explore the sky through a combination of speed, depth, and precision,” Juri 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.”
Researchers can view the orbit of 2026 ED138 using Orbitviewer, an interactive web application that displays the solar system in three dimensions. Operations at the Vera C. Rubin Observatory are funded by the U.S. National Science Foundation and the U.S. Department of Energy’s Office of Science.
Source: ScienceDaily
