Scientists discover backward star, spinning in the opposite direction to its planets


Artist’s rendering of the exoplanetary system K2-290, showing the main star K2-290 A, its two planets, and the smaller companion star K2-290 B in the background.

Christoffer Grønne (artist)

In planetary systems, it’s generally expected planets and their stars rotate in the same direction. Take our own solar system, for example.

Our sun spins in almost the exact same direction as Earth and the rest of the planets orbits, with a small six degree tilt. It was once assumed that all systems work in a similar way, but research has shown that isn’t necessarily the case

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There have been a few stars discovered that spin differently to a planet that orbits them, but a recent study has found one star rotating in the opposite direction to not one, but two planets in its system.

The K2-290 system contains a total of three stars, with two planets orbiting its main star, K2-290 A. The interesting part? K2-290 A is rotating at a 124 degree tilt compared to the two planets that orbit it. Meaning it’s rotating in the opposite direction. 

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Maria Hjorth and Simon Albrecht from Aarhus University in Denmark made the discovery, and published their findings in the journal Proceedings of the National Academy of Sciences on Monday.

The two planets orbiting K2-290 A exist on the same plane, so explaining the direction difference becomes a little more complex.

“The fact that [the planets] appear to be coplanar means that maybe it wasn’t a dynamically violent mechanism that caused them to migrate, maybe it was the disc,” Chris Watson of Queen’s University Belfast, told New Scientist. “So then, you have to look at how did you end up with the star and the planet-forming disc tilted in the first place?”

Albrecht and his colleagues believe that, given this system has three stars, “gravitational torques from companion stars” are most likely the cause of K2-290 A’s unique rotation. The other stars in the K2-290 system might be playing havoc with the spins and orbits. 

“The unique aspect of K2-290 is that a companion star has been detected (K2-290 B),” read the study, “with properties that make it a good candidate for the misalignment of the protoplanetary disk.”


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