Rubin Observatory Finds Massive Dwarf Planet Candidate Beyond Pluto
Astronomers using the Vera C. Rubin Observatory identified 2026 ED138, a distant object estimated to be 600–1,500 kilometers wide. It remains a candidate, and…
Astronomers using the Vera C. Rubin Observatory found an enormous dwarf planet candidate beyond Pluto, identified as 2026 ED138, in observations collected earlier in 2026. The object may measure between 600 and 1,500 kilometers wide, but researchers say it is not yet officially classified as a dwarf planet.
If confirmed, ED138 would join the recognized dwarf planets and rank among the largest bodies found in the Solar System’s outer regions. Its discovery also offers a first look at how Rubin’s survey could reveal objects that have remained hidden among the crowded stars near the Milky Way.
Why is 2026 ED138 still a candidate?
Scientists still need to establish the object’s physical size before confirming its classification. Matthew Holman, a Rubin Operations team member who discovered ED138, said that process would take further observations.
“At this point, it’s still a candidate. We really need to know how physically big it is, and that will take a few months, probably,” Holman said.
Holman identified the object while analysing Rubin data with a computer program that searches billions of detections of moving objects and matches observations that may belong to the same body. He said its brightness and distance suggested it was unusually large. His first response was “excited disbelief,” followed by checks for an error in the code or a false detection.
To examine the finding, Holman worked with Mario Jurić, Rubin’s Solar System lead scientist. Jurić searched Rubin’s catalog and found 20 additional observations of ED138 dating back to March 2026. Researchers also used other sources to trace its orbit as far back as 10 years.
How large and distant is the object?
Astronomers estimate ED138 is between 600–1,500 km (370–930 miles) wide. It is currently about 46 astronomical units (AU) from the Sun; one AU is the average distance between Earth and the Sun. Pluto orbits at an average distance of 40 AU.
ED138 is a trans-Neptunian object, meaning it orbits beyond Neptune. Its orbit is tilted nearly 25 degrees from the plane of the Solar System, a feature astronomers say places it in the hot-classical trans-Neptunian object group. The tilt also suggests gravitational interactions with Neptune disturbed its original orbit.
The candidate sits in a difficult patch of sky. It was found near the plane of the Milky Way, where millions of stars make moving objects harder to spot. Its location in the southern sky also made it difficult to observe from the Northern Hemisphere, Holman said.
That matters because ED138’s earlier invisibility was not simply a question of size. Telescopes and searches focused elsewhere could miss a moving object against a dense field of stars. Rubin’s regular monitoring of the Southern Hemisphere sky, combined with algorithms that sift through millions to billions of points of light, helped the team pick it out.
“People don’t typically search for things in the Milky Way, because there’s so many stars that it’s really hard to find moving objects,” Holman said.
What could Rubin find next?
The Vera C. Rubin Observatory detected ED138 while preparing for the Legacy Survey of Space and Time, a 10-year survey of the southern sky. Its ability to repeatedly capture changes across a wide area helped researchers identify the object and connect observations made at different times.
Holman said there might be “a handful” of other objects around ED138’s size for Rubin to find. The candidate is also bright enough that capable amateur observers could see it if they know where to look, he said, though it is not visible to the naked eye.
Edward Ajhar, NSF Program Director for Rubin Observatory, said the telescope’s ability to capture movement among many objects would expand scientists’ understanding of the Solar System, the Milky Way and other galaxies.
For now, the classification hinges on confirming ED138’s size: researchers estimate it could span as much as 1,500 kilometers.
