New research shows that star-snuggling hot Jupiters, despite being only a thousandth of the mass of their host suns, make their host stars wobble like a spinning top.

Top image: Artistic impression via Hubble Space Telescope.

Hot Jupiters were among the very first exoplanets ever discovered. Their existence caught astronomers completely off-guard, not only because they defied notions of what solar systems were supposed to look like, but also because they had no idea how gas giants could exist so closely to their parent stars, distances that are shorter than Mercury is to our own Sun.

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What's more, unlike our solar system, in which the sun's rotational axis is (approximately) aligned with the orbital axis of all the planets, Hot Jupiters feature orbital axes that are misaligned with those of their host stars. This spin-orbit misalignment has puzzled astronomers for years.

Astronomers are starting to understand what's going on — and the fact that Hot Jupiters only exist in binary star systems is an important clue.

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These gas giants end up where they are as the result of an inward migration from the outer realms of the solar system. As noted by Cornell astronomer and study co-author Dong Lai , partner binary stars — which can be as far away as hundreds of astronomical units — influence the giant Jupiter-like planets with gravity, causing them to falter into uncommon orbits. That, in turn, is what causes them to migrate inward close to their sun.

Image: Lai/Cornell

But that's not the whole story. By simulating the dynamics of these odd planetary system, Lai and his team showed that when the gas giant approaches its host star, it can force the star's spin axis to precess (i.e. to change the orientation of their rotational axis), much like a wobbling, spinning top.

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"Also, it can make the star's spin axis change direction in a rather complex — or even a chaotic — way," added Lai in a Cornell press release. "This provides a possible explanation to the observed spin-orbit misalignments and will be helpful for understanding the origin of these enigmatic planets."

Read the entire scientific article: "Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters."