Astronomers have identified a candidate dwarf planet beyond Pluto using data from the Vera C. Rubin Observatory in Chile. Provisionally named 2026 ED138, the icy object may be among the largest trans-Neptunian bodies discovered so far. Its estimated diameter is between 600 and 1,500 kilometers, although its exact size and nature remain unconfirmed.

The discovery was announced on October 27 by researchers from the Harvard-Smithsonian Center for Astrophysics and the University of Washington. It is the first dwarf planet candidate identified using data from the observatory. Astrophysicist Matthew Holman found the object on October 13 while analyzing observations from 2026 with software developed with colleague Kevin Napier. The system searches billions of detections for repeated observations of the same moving object.

To verify the finding, Mario Jurić, a University of Washington astronomy professor and leader of Rubin’s Solar System research team, reviewed the observatory’s records. He found 20 additional observations dating back to March. The team also located earlier images from other astronomy surveys, some from 2016, allowing researchers to reconstruct more than a decade of the object’s orbit.

2026 ED138 is currently about 46 astronomical units from the Sun. One astronomical unit is roughly the average distance between Earth and the Sun; Pluto’s average orbital distance is about 40. The object is therefore classed as trans-Neptunian, meaning it orbits the Sun farther away than Neptune.

Researchers estimated its possible size from its distance, observed brightness and an assumed ability of its surface to reflect sunlight. Icy bodies of this size are expected to have enough mass for gravity to make them roughly spherical, one requirement for dwarf-planet status. But the object’s shape has not been confirmed, and its diameter remains uncertain, so it is still considered a candidate.

If confirmed, 2026 ED138 could join the five dwarf planets officially recognized by the International Astronomical Union: Pluto, Ceres, Eris, Haumea and Makemake. Jurić put its likely diameter at about 1,000 kilometers and said it would be the largest trans-Neptunian body discovered in roughly 20 years.

The object was found near the plane of the Milky Way, where a dense background of stars makes faint, distant Solar System bodies difficult to distinguish. Repeated observations of the southern sky by Rubin, combined with software that links detections made at different times, helped researchers identify it among the many sources of light.

The discovery came as the observatory was still commissioning its telescope. Its Solar System team had reported observations of more than 11,000 new asteroids in April 2026, including about 380 trans-Neptunian objects. The observatory’s Legacy Survey of Space and Time began in June and is designed to repeatedly observe the sky over ten years. Researchers say this ongoing survey can help find faint objects and refine their orbits by connecting new detections with older records.

Further observations will be needed to establish 2026 ED138’s properties and classification. Studying trans-Neptunian objects can also help researchers investigate the formation and evolution of the Solar System, including changes to the orbits of the giant planets and the dispersal of smaller bodies.

Sources: elDiario.es.