Hot Jupiters can make their host stars wobble

New observations show exoplanets can knock their suns off balance

Distant companion stars can knock planetary orbits wildly off course.
Image credit: Cornell University

Large, gaseous exoplanets close to their parent sun, known as hot Jupiters, can knock their stars off balance, despite the vast difference in size.

In our Solar System, the rotation axis of our Sun is roughly at right angles to the plane of the planets in orbit around it. However in systems with hot Jupiters recent observations show that the parent stars are sometimes misaligned.

"Although the planet's mass is only one-thousandth of the mass of the sun, the stars in these other solar systems are being affected by these planets and making the stars themselves act in a crazy way," said Dong Lai, a professor of astronomy at Cornell University.

These massive exoplanets weren’t always this close to their parent star, instead having orbits similar to Jupiter and Saturn around our own Sun. But when the sun’s partner binary star passed nearby it influenced the gravity of the giant planet and threw its orbit into chaos, resulting in an unlikely orbit, close to the stellar surface.

"When exoplanets were first found in the 1990s, it was large planets like Jupiter that were discovered. It was surprising that such giant planets can be so close to parent star," Lai said. "Our own planet Mercury is very close to our sun. But these hot Jupiters are much closer to their suns."

As the hot Jupiters get in close the planet can knock the stars’ spin axis, causing it to wobble like a spinning top, according to simulations run at Cornell.

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


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