Massive 'Hot Jupiters' Cause Their Host Stars to Wobble Like a Spinning Top

It turns out that "hot Jupiters" have more of an effect on their host stars than scientists once though. Astronomers have found that these large, gaseous exoplanets can make their stars wobble when they pass through their own solar systems and wind up near their suns.

"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, senior author of the new paper describing the findings, in a news release.

Hot Jupiters are large, gaseous planets that can be found throughout the universe in distant planetary systems. They orbit extraordinarily close to their own host stars.

In our own solar system, the sun's rotation axis is aligned with the orbital axis of all of the planets. This orbital axis is perpendicular to the flat plane in which the planets revolve around the sun. In systems with hot Jupiters, though, the orbital axis of these planets is misaligned with the rotation axis of the host star.

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

In order to examine the dynamics occurring between host stars and hot Jupiters, the scientists simulated the interactions of these planetary systems. They found that when a Jupiter-like planet approaches its host star, the planet can force the star's spin axis to precess, which means that it changes the orientation of its rotational axis. To put it more simply, it causes the star to wobble slightly like a spinning top.

"Also, 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."

The findings are published in the journal Science.