Rubin Observatory Spots Object Past Neptune Orbiting Against the Planets

The Rubin Observatory in Chile has found an object just beyond Neptune that circles the sun on a steeply tilted, retrograde orbit, EarthSky reported. The object, temporarily labeled R631, moves in the opposite direction from most planets, and its orbit is inclined 142 degrees to the plane of the solar system.

Much of what is known so far, including its orbit and size, is an early estimate based on a few months of observations. Here are the main questions about the find.

What exactly is R631?

R631 is a distant object in the outer solar system. Its name is only a placeholder from the Rubin data, and EarthSky said the Minor Planet Center will soon give it an official designation. Both astronomers and citizen observers who watch Rubin's public alert stream noticed it. It showed up in observations made from December 2025 through March 2026, a span of four months.

According to EarthSky, R631 sits 32 astronomical units (AU) from the sun. An AU is the Earth-sun distance, so that is 30 times the distance from Earth to the sun. Neptune orbits at 30 AU.

What does retrograde mean here?

In everyday use, retrograde suggests something moving backward. In astronomy, EarthSky explained, the term has a precise meaning: any object whose orbit is tilted more than 90 degrees from the solar system's plane is in retrograde motion. Most planets, moons and asteroids move in the same direction around the sun, counterclockwise as seen from above Earth's north pole. At 142 degrees, R631's orbit is tilted past perpendicular and slices through the plane at a steep angle.

How big is it, and how long is its orbit?

If the orbit calculated so far is correct, R631 needs about 547.84 Earth-years to circle the sun once. It will reach its closest point to the sun, called perihelion, on Oct. 31, 2047, at a distance of 24 AU.

The size is much less certain. Physicist and astronomer Marshall Eubanks said on the Minor Planet Mailing List that the object could be 62 miles (100 km) across. He suggested it might resemble Comet Bernardinelli-Bernstein, the largest known Oort cloud comet. That is one researcher's comment, not a published measurement.

Where could such an orbit come from?

EarthSky outlined several possibilities, none confirmed. R631 might have formed around another star and been flung out of that system before being captured by the sun's gravity. It might instead have begun in an ordinary orbit in our own solar system and been kicked into a retrograde path by a close pass of a large object such as Jupiter or a passing star.

Amateur astronomer Sam Deen, who searches archival data for lost asteroids and comets, said the object most likely comes from the Kuiper belt. He said it was destabilized when it passed too close to Neptune at some point in the past billion years.

Is it related to the famous sungrazer comets?

The 142-degree tilt matches that of the Great Comet of 1882, which broke apart during a very close pass of the sun, and of Comet Ikeya-Seki, which did the same in October 1965. Both belong to the Kreutz sungrazer family, whose members follow similar orbits that carry them very near the sun. Scientists think the family descends from a single ancient comet that fragmented.

EarthSky said Tony Dunn ran a simulation comparing the Kreutz sungrazers with R631 and the rest of the solar system. According to the outlet, it showed that R631 is unrelated.

Why does it matter?

R631 is no threat and will not be visible to the naked eye, and the sources describe no effects on daily life. Its interest is scientific. An object on such a tilted orbit gives astronomers a test case for ideas about how bodies get thrown into unusual paths, whether from inside the solar system or from beyond it.

It also offers something to watch for. EarthSky said that if R631 is cometary, it might show activity such as outgassing around its 2047 perihelion. The outlet noted that Comet Bernardinelli-Bernstein was seen releasing jets from 16.6 AU in a June 2025 report. Whether R631 is a comet or a rocky body has not been settled.

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Around Prague, based on reporting by EarthSky