Rubin Observatory discovers dwarf planet candidate 2026 ED138 — ScienceAlert

Astronomers have discovered a large trans-Neptunian object, 2026 ED138, in the Kuiper Belt that may qualify for dwarf planet status. According to ScienceAlert, it was detected by the Vera C. Rubin Observatory during a survey of the southern sky. The object's diameter is preliminarily estimated at between 600 and 1,500 kilometers.

2026 ED138 may be one of the largest objects discovered in trans-Neptunian space. Its possible size is compared with those of the dwarf planets Makemake and Haumea, although the body's precise parameters have yet to be determined.

Archival data on the object

On October 13, 2026, astrophysicist Matthew Holman of the Harvard-Smithsonian Center for Astrophysics was analyzing Rubin Observatory data using software developed with his colleague Kevin Napier when he noticed the object's unusual motion. The researchers tracked 2026 ED138 through 30 detections over 20 nights, from March 4 to July 11, 2026.

Later, the team found the object in archival images from the Dark Energy Camera taken as early as February 2016. It was also recorded in 2017, 2018, 2019, and 2023. These archival data made it possible to characterize the celestial body's orbit.

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Orbit and size

According to the Minor Planet Center, 2026 ED138 orbits the Sun in approximately 281 years. At the point of its orbit closest to the Sun, it is at a distance of 36.86 astronomical units, and at the farthest point, 49.04 astronomical units. By comparison, Pluto travels in an orbit ranging from 29.6 to 49.08 astronomical units from the Sun.

The average distance of 2026 ED138 from the Sun is about 42.95 astronomical units. The object's orbit is inclined by approximately 24.5 degrees to the plane of the Solar System, and its position against the dense star field of the Milky Way made detection by previous surveys more difficult.

The exact diameter of 2026 ED138 remains unknown, since brightness depends not only on size but also on the surface's reflectivity. If the size estimate is confirmed, the object's gravity may be sufficient to form an approximately spherical shape, one of the characteristics of a dwarf planet. Further infrared observations should help refine its size and status.