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Why this is the case, and how you actually measure \u201cspin\u201d on a gas giant like Jupiter, is an interesting question, something that scientists have only recently been able to grapple thanks to results from a NASA spacecraft orbiting Jupiter, called\u00a0Juno.<\/p>\n
Rotation, rotation, rotation<\/strong><\/p>\n Measuring spin on a gas giant like Jupiter compared to a rocky planet like Earth is a little tricky. \u201cIt\u2019s not like you can look at the surface,\u201d said Ravit Helled at the University of Zurich in Switzerland. Jupiter is\u00a0almost entirely composed of hydrogen and helium, a giant gaseous ball spinning in space. So how do we know how fast it\u2019s actually spinning?<\/p>\n We calculate this by studying the planet\u2019s magnetic field. Measuring the planet\u2019s radio emissions, we can work out the spin of its internal magnetic field, in turn giving us the spin of the planet. \u201cWe\u2019re finding periodicities in the magnetic fields,\u201d said Helled. This same technique allows us to measure the spins of the other gas giants, too.<\/p>\n Juno, which entered orbit around Jupiter in 2016, also used gravitational measurements to determine how Jupiter spins. The spacecraft has shown that the winds in the planet\u2019s outer atmosphere extend down about 3,000 kilometers (1,900 miles) into the planet. \u201cFor decades it was not known if the winds penetrate very deep into the interior,\u201d said Helled, a member of the Juno science team. \u201cThanks to Juno we could constrain the depth. Now we believe below 3,000 kilometers, the planet reaches uniform rotation.\u201d<\/p>\n Spinning up<\/strong><\/p>\n Where Jupiter gets this rotation rate from is another important question, and the answer might again lie in the planet\u2019s magnetic fields. When the planet first formed 4.6 billion years ago, it accumulated mass from the disk of material around the young Sun. As it grew in size it would have spun faster and faster as its angular momentum increased, like a spinning ice skater drawing in their arms.<\/p>\n<\/div>\n