Astronomers have found a world beyond Neptune that orbits the Sun backwards.
The object, temporarily called R631, circles the Sun at a steep 142-degree tilt to the plane of the solar system. The Vera C. Rubin Observatory in Chile spotted it in data gathered between December 2025 and March 2026. It sits about 32 astronomical units from the Sun, just past Neptune, which orbits at 30.
Physicist Marshall Eubanks, who flagged the object on the Minor Planet Mailing List, estimated it at roughly 100 kilometres across. Astronomers have not yet settled whether R631 is a rocky body or a comet, and two ideas compete over how it got there. Neptune may have flipped its orbit long ago, or it may have arrived from another star system entirely.
R631 will reach its closest point to the Sun on 31 October 2047, at 24 astronomical units, and takes about 548 years to complete one orbit. The Minor Planet Center will assign it an official designation as astronomers keep tracking it.
Source: Gizmodo
