A Planet Twice Earth's Size Is Orbiting Its Star Backward

A planet 73 light-years away is circling its star the wrong way. GJ 3090 b has a highly misaligned orbit. It's traveling in the opposite direction to its star's rotation, which is not supposed to happen.

Stars and planets form from the same collapsing cloud of gas and dust, which flattens into a spinning disk. Everything that emerges from that disk should be traveling in the same direction.

There are known ways a planet can get flipped. Gravitational interference from a massive companion, such as a gas giant, a brown dwarf or another star, can torque an orbit over time into something that looks completely unhinged. Astronomers looked for one.

They didn't find one.

Researchers measured the tilt of GJ 3090 b's orbit at roughly 136 degrees. Anything past 90 means the planet is going backward. Earth's orbit, for comparison, sits about 7 degrees off the sun's spin. It's the first backward-orbiting planet found around an M dwarf, the small, cool type of star that makes up most of the stars in the galaxy.

That leaves a hypothesis stranger than the problem it's trying to solve: the star may have pulled in a second disk of gas and dust from its surrounding environment, one oriented differently from the first, and GJ 3090 b formed from that crooked material and simply inherited the mess. Researchers emphasize that this scenario still needs additional observations to confirm.

GJ 3090 b isn't alone. It shares its star with at least one other planet, and if the second-disk idea is right, that one is probably going backward too.

Read the full story at Space.com, September 22, 2026

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