Object 2026 ED138 was in photos taken in 2016, but no one spotted it. Matthew Holman of the Harvard-Smithsonian Center for Astrophysics found it on 13 October 2026 in Vera Rubin Observatory data gathered earlier this year. The observatory announced the find on 27 October. It is a dwarf planet candidate, not a recognised one: its size is a rough estimate, and no one has yet checked whether it is round enough.
The object lies about 46 times as far from the Sun as Earth does. Pluto's average distance is about 40 times. Its orbit is tilted at almost 25 degrees to the plane in which the planets move, so astronomers place it among the "hot classical" objects beyond Neptune. That is the name for bodies whose orbits Neptune's gravity has most likely bent.
Moving from night to night
ED138 sits in a part of the sky next to the plane of the Milky Way, where there are millions of stars. There, a faint moving speck gets lost among background sources of light, and most telescopes cannot tell it apart from them.
In a single frame the object is a dot like any other. Only its movement from night to night gives it away. The code Holman wrote with his colleague Kevin Napier matches billions of detections and looks for those that belong to the same body. Holman ran the code on the 2026 data and saw the result the same evening. "My first reaction was excited disbelief," he said.
Its brightness and distance suggested the object is unusually large for its location. Rubin's Simonyi telescope photographed it 30 times on 20 nights between 4 March and 11 July 2026. Mario Jurić of the University of Washington, the scientist who leads the project's Solar System work, checked the catalogues and found more observations.
Next came "precovery", in which astronomers search old images for an object already known. The orbit from the new data showed where to look back in time. Images from the Dark Energy Camera, found through the Asteroid Institute's ADAM Precovery service, showed the object from more than ten years ago. That let the team trace its orbit over the whole period.
Surface reflectivity not measured
The size estimate, from 600 to 1,500km, comes from three values: distance, brightness and assumed surface reflectivity. The reflectivity itself has not been measured. A bright object may be large and dark, or smaller and shiny, and in visible light the two cases look the same. So the team is waiting for infrared measurements.
A round shape is a condition for a dwarf planet. The team says icy bodies of this size are expected to be round if their own mass has shaped them, but this has not yet been checked.
The official list of the International Astronomical Union has five dwarf planets: Pluto, Ceres, Eris, Haumea and Makemake. If ED138 joins it, it will be the sixth. Holman said the object would then join a very small family of worlds. There is no deadline for a decision.
This is the first dwarf planet candidate announced by Rubin. The observatory's 10-year survey of the southern sky, the Legacy Survey of Space and Time, began in June 2026 and may find more hidden objects. Scientists around the world can organise the next observations. The images are available to holders of Rubin data rights, and the orbit can be viewed in the Orbitviewer app.