When Voyager 1 flew past Jupiter more than four decades ago, it recorded radio waves produced by the planet. Scientists use these and other radio studies to learn about the solar system’s largest planet — its auroras, the strength of its magnetic field, links to its big moons, and more.

The radio waves have been especially helpful in figuring out the length of Jupiter’s day. Because the planet is a big ball of gas, there are no solid features to tell us how fast Jupiter spins. To make it even tougher, cloud bands in Jupiter’s upper atmosphere move in opposite directions.

The radio waves are produced by the motions of different layers deep within the planet. The motions generate a powerful magnetic field. As Jupiter spins, the magnetic field gives particles around the planet a charge. That causes them to emit radio waves. So those waves tell us Jupiter’s internal rotation rate, which is the official definition of a Jovian day: nine hours, 55 minutes, and 30 seconds — the shortest day of any planet in the solar system.

Jupiter is putting in its best showing of the year. It’s opposite the Sun, so it’s in view all night. It’s also closest for the year, so it shines brightest. It looks like a brilliant star. It’s low in the east at nightfall, arcs across the south later on, and is low in the west at first light.

More tomorrow.
 

Script by Damond Benningfield

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