Planetary Spins

A day on Jupiter and on Saturn lasts about 10 hours. What set this spin rate? Spin measurements of younger gas giant planets, orbiting other stars, may hold the answer.​

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When planets are born, they contract by orders of magnitude, spinning up due to conservation of angular momentum. However, the planet's magnetic field can interact with a surrounding gas disk to spin the planet down. We think that the interplay of these two effects sets the planetary spins that we observe.​

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See Ginzburg & Chiang (2020) for details.