New dwarf planet candidate found in deep space

Astronomers have identified a new dwarf planet candidate in the outer solar system, provisionally designated ED138. If future observations confirm its status, the object will join a group of five recognized dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris. The discovery comes from data collected by the Vera C. Rubin Observatory, a facility atop a 2,682-meter mountain in Chile that houses the world’s largest digital camera. The telescope began operating in 2025 and can image the entire sky every three days.

Matthew Holman, a senior astrophysicist at the Smithsonian and lecturer at Harvard University, ran a computer program he co-developed to analyze Rubin data from early 2026. The software scanned billions of detections of moving objects. When ED138 appeared in the results, Holman initially reacted with excited disbelief and checked for errors. He worked with Mario Jurić, the Rubin Solar System lead scientist and a professor at the University of Washington, to verify the find. Jurić located 20 additional observations of the object in the Rubin catalog dating back to March 2026. Using other data sources, the team plotted the object’s orbit back ten years.

Holman notes that ED138 is not yet officially classified as a dwarf planet. The team needs to determine the object’s physical size, a process that will likely take several months. Current estimates place the diameter between 600 and 1,500 kilometers. This size would make it larger than Ceres, the smallest recognized dwarf planet. The object orbits the sun at a distance of approximately 46 astronomical units, placing it beyond Pluto and categorizing it as a trans-Neptunian object.

The object is not visible to the naked eye, but Holman says capable amateur astronomers can see it if they know where to look. Its location in the southern hemisphere made it difficult to detect from northern hemisphere observatories. Additionally, ED138 has been moving along the plane of the Milky Way for the past 20 years. The high density of stars in that region obscures moving objects, making them harder to spot. Holman says this location ruled out many telescopes that might have otherwise found the object.

Michele Bannister, an associate professor at the University of Canterbury who was not involved in the discovery, called the object scientifically interesting. She noted that its size allows scientists to consider it a world. Other telescopes will now track the object to gather more data. Bannister suggested that a future spacecraft mission could reveal surface features such as nitrogen glaciers, similar to those on Pluto. However, she emphasized that current knowledge is limited to the object's size, with other physical characteristics remaining unknown.

The discovery is part of a growing list of objects detected by the Rubin telescope, which includes many asteroids and smaller trans-Neptunian objects. Holman estimates there may be several more objects of similar size that the telescope could find. If ED138 is confirmed, astronomers will assign it a permanent number and a name. Holman said people have already emailed name suggestions, but the process for selecting the final name is not yet defined.