Jupiter weather forecast: Lightning with a chance of mushballs

New Juno observations suggest the gas giant’s thunderstorms are filled with antifreeze.
By | Published: August 14, 2020 | Last updated on May 18, 2023
This artist’s rendition shows shallow lightning like the kind the Juno spacecraft spotted in storms on Jupiter’s dark side.
NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt/Heidi N. Becker/Koji Kuramura

During late summer, the U.S. is often hammered by roiling storms and buffeted by icy hail. But on Jupiter, it’s always thunderstorm season.

Scientists have known about lightning on the gas giant since the Voyager spacecraft spotted it in 1979. Now, observations made by the Juno spacecraft, which is currently orbiting the planet, are tweaking our understanding of where and how Jupiter produces its lightning, as well as what kind of weather accompanies it.

Earth’s clouds, which are made of water vapor, can become electrically charged and generate lightning. When enough charge is built up within the cloud, it sparks a lightning bolt. Jupiter has water clouds, too, but they’re fairly deep in its atmosphere — between 28 and 40 miles (45 to 65 kilometers) below the visible cloud tops, where the temperature is almost freezing. But Juno spotted shallow lightning striking much higher, about 16 miles (25 km) above where these water clouds are thought to exist. At that altitude, temperatures drop below –126 degrees Fahrenheit (–88 degrees Celsius), which is far too cold for liquid water or water vapor.

From Astronomy’s February 2018 issue:
A planetary science expert explains how clouds form on Jupiter.

This artist’s illustration outlines how Jupiter produces “shallow lightning” and “mushballs.”
But Jupiter’s atmosphere contains much more than just water. And one of those components is ammonia, which makes great antifreeze. Based on the shallow lightning sightings, researchers now think that Jupiter’s deeper thunderstorms fling water closer to the cloud tops, where it mixes with ammonia and forms clouds capable of developing electric charge.

There’s one more consequence of these strange, ammonia-water storms: ammonia-water hail, known on Jupiter as “mushballs.” On Earth, hail forms when an airborne drop of water freezes into a core. This frozen drop then gets tossed around within thunderclouds by high winds, gaining more and more ice layers. Eventually, it gets too heavy for the winds to keep it afloat and it falls down to the ground. The cores of Jupiter’s hail are water-ammonia slushballs rather than hard, icy pellets (remember, ammonia acts as antifreeze, so the balls are slushy instead of solid ice). These, too, are flung around thunderstorms, gathering layer after layer of ice, until they’re too heavy and fall lower in the atmosphere, where warmer temperatures evaporate them.

Such mushballs are the slushy solution to an ongoing problem: Jupiter’s missing ammonia. For some time, scientists have noticed small “pockets” in Jupiter’s atmosphere that are strangely devoid of ammonia, despite it being so widespread. If the ammonia in these regions is swept up by thunderstorms and dropped lower into the atmosphere — below where we can detect it — as mushballs, the conundrum disappears.

Earth’s weather may seem violent and extreme at times, but at least we don’t have to worry about slushy, antifreeze-laden hail falling from the sky.