Rubin telescope identifies ED138, a potential sixth dwarf planet

Astronomers have identified a new celestial body named ED138 that may become the sixth recognized dwarf planet in the solar system. The object was detected by the Vera C. Rubin Observatory in Chile, a facility that began operations in 2025 and holds the world's largest digital camera. It orbits the sun at a distance of approximately 46 astronomical units, a position that places it well beyond the orbit of Pluto.

Matthew Holman, a senior astrophysicist at the Smithsonian Institution and a lecturer at Harvard University, discovered the object in 2026. Holman used a computer program he helped develop to scan billions of detections from Rubin's data. He initially described his reaction as "excited disbelief" and immediately checked for errors in the software or false positives. To verify the detection, Holman collaborated with Mario Jurić, the Rubin Solar System lead scientist and a professor at the University of Washington. Jurić located 20 additional observations of the object in Rubin's catalog dating back to March 2026. Using other data sources, the team plotted the orbit of the object over a period of 10 years.

The estimated diameter of ED138 ranges from 600 to 1,500 kilometers. This size makes it larger than Ceres, which is currently the smallest of the five dwarf planets recognized by the International Astronomical Union. The other recognized dwarf planets are Pluto, Haumea, Makemake, and Eris. Despite its size, the object is not visible to the naked eye. Holman noted that capable amateur astronomers could see it if they knew the specific location in the sky.

Holman stated that ED138 is not officially a dwarf planet yet. He explained that the team needs to determine the physical size of the object with greater precision, a process that will likely take several months. The object belongs to the class of trans-Neptunian objects, which orbit the sun at a distance greater than Neptune's.

Scientists had not previously discovered ED138 because of its location in the southern hemisphere. Holman noted that this position makes it difficult to observe from the northern hemisphere, where most sky-searching telescopes are located. Additionally, the object has been moving across the plane of the Milky Way for the past 20 years. Holman explained that astronomers typically avoid searching in the Milky Way because the high density of stars makes it difficult to spot moving objects.

Michele Bannister, an associate professor at the University of Canterbury in New Zealand, commented on the discovery. She was not involved in the identification of ED138. Bannister said the object is scientifically interesting because it is a large trans-Neptunian object that is still fainter than what can be seen with the naked eye. She added that other telescopes will now work to determine the physical characteristics of the world. If ED138 is confirmed, astronomers will assign it a permanent number and a name, a process that may take time.