Astrology

Rubin Observatory finds an object orbiting backward beyond Neptune

The Vera C. Rubin Observatory in Chile has found an object beyond Neptune that orbits the sun in the opposite direction from most planets, EarthSky reports. The object, temporarily designated R631, follows a steeply tilted path through the solar system.

R631 appeared in Rubin data over four months, from December 2025 through March 2026, according to EarthSky. Astronomers and members of the public who follow the observatory's alert stream noticed it in the observations.

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R631 follows a steep retrograde orbit#

EarthSky reports that R631 has an orbital inclination, or tilt relative to the solar system's plane, of 142 degrees. Astronomers classify an orbit as retrograde when its tilt exceeds 90 degrees. Most planets, moons and asteroids travel in roughly the same direction and in a relatively flat plane.

The object is about 32 astronomical units from the sun, EarthSky reports. An astronomical unit is the Earth-sun distance. Neptune, the eighth planet, orbits at about 30 astronomical units, placing R631 just beyond its orbit at present.

R631 is not the first object found on a retrograde orbit. EarthSky notes that the Great Comet of 1882 also had an inclination of 142 degrees. The Minor Planet Center is expected to give R631 an official designation; its current label is temporary.

Rubin has found other distant objects#

Rubin's survey has also identified a separate object beyond Neptune, provisionally named 2026 ED138, that may qualify as a dwarf planet. Sci.News reports that researchers used its brightness, distance and assumed reflectivity to estimate a diameter of between 600 and 1,500 kilometers.

Astrophysicist Matthew Holman identified 2026 ED138 while processing Rubin observations, and astronomer Mario Jurić found additional detections. According to Yahoo, images from archives showed it had been observed as early as 2016, and Rubin recorded it 30 times between March and July 2026.

Infrared observations are needed to establish the size of 2026 ED138 more precisely, Sci.News reports. For R631, EarthSky gives October 31, 2047, as the date it reaches its closest point to the sun, at a distance of 24 astronomical units.

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