‘Exotic’ lightning crackles across Jupiter’s cloud tops

The flashes of light could form thanks to ammonia antifreeze

Jupiter clouds

Wispy, white “pop-up” clouds on Jupiter, seen in this enhanced image from NASA’s Juno spacecraft, could mark spots where ice crystals are thrown upward by raging storms below. Those ice crystals could then help form newfound lightning in Jupiter’s cloud tops.

Gerald Eichstädt, Sean Doran, MSSS, SwRI, JPL-Caltech/NASA (CC BY-NC-SA)

Small, frequent lightning storms zip across Jupiter’s cloud tops. NASA’s Juno spacecraft spotted the flashes for the first time, scientists report August 5 in Nature.

“It’s a very exotic thing that doesn’t exist on Earth,” says physicist Heidi Becker of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

Previous spacecraft have revealed high-energy “superbolts” on Jupiter. That lightning originates 50 to 65 kilometers below Jupiter’s cloud tops, where liquid water droplets form. Scientists think superbolts form like lightning on Earth does: Colliding ice crystals and water droplets charge each other up, then stretch the charge between them when they separate (SN: 6/25/20).

Juno, which arrived at Jupiter in 2016, got much closer to the giant planet’s cloud tops than previous missions. Becker and her team turned the spacecraft’s navigation camera — which normally observes stars to track Juno’s position — on Jupiter’s nightside in February 2018. To the team’s surprise, the clouds crackled with electricity.

Lightning on Jupiter
Newly observed lightning showed up as bright dots (indicated with arrows) on Jupiter’s nightside, seen in this composite image from one of Juno’s cameras. The insets are pixelated representations of the events’ brightness (yellow is more bright; blue is less bright).H.N. Becker et al/Nature 2020

Superbolts are up to 100,000 times as strong as these small flashes. But the cloud-top lightning is 10 times as frequent. Strangely, the smaller bolts appeared to come from just 18 kilometers below the cloud tops, where it’s too cold for liquid water to exist alone.

Shallow lightning must have a different origin than the deeper lightning, Becker says. Perhaps ammonia in the upper cloud decks acts as antifreeze, creating droplets of ammonia and water combined. Juno has also seen evidence that violent storms in deeper cloud layers sometimes toss ice crystals high above where they’re normally found. When those crystals collide with the ammonia-water droplets, they may charge up and create lightning, Becker and her colleagues reason.

Similar small lightning storms may happen on other planets, including exoplanets, Becker says (SN: 5/13/16). “Every time you have a new realization, it feeds into new theories that will be developed not only for our solar system but for other solar systems.”

Lisa Grossman is the astronomy writer. She has a degree in astronomy from Cornell University and a graduate certificate in science writing from University of California, Santa Cruz. She lives near Boston.

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