A thunderstorm that raged in Jupiter鈥檚 atmosphere for weeks was fortuitously captured by NASA鈥檚 Juno spacecraft, giving astronomers the most detailed look ever at a storm on the gas giant.
On 29 November 2021, Juno passed directly over a 3400-kilometre-wide thunderstorm that had been tracked by astronomers on Earth since it started nearly two weeks earlier. Juno鈥檚 close approach, about 5700 kilometres above the storm, meant that at Michigan Technological University and his colleagues could analyse data from three of Juno鈥檚 on-board instruments, in visible, microwave and infrared light.
鈥淲e haven鈥檛 flown over another Jupiter thunderstorm with this level of detail,鈥� says Brueshaber. 鈥淭he microwave radiometer and the visible camera have to be able to sweep the storm almost over the top to get this really good data. We haven鈥檛 done that yet again, and we might not鈥� this was very fortuitous.鈥�
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One puzzling feature of the storm was its persistence, he says. 鈥淎ll the numerical models to date that have tried to simulate a single thunderstorm, they last maybe hours, not weeks.鈥� This might be explained by an unusually strong concentration of ammonia and water vapour humidity and a relative absence of it nearby, says Brueshaber, which is similar to thunderstorms on Earth that are formed and sustained by strong gradients of water vapour.
The ammonia-rich storm could also produce rain-like 鈥渕ush balls鈥� of water and ammonia that rain down into the atmosphere below, he says.
They also found the storm was relatively unconnected to deeper features lower in Jupiter鈥檚 atmosphere, unlike some of the more permanent features such as its Great Red Spot, and is self-contained in a weather layer, similar to storms on Earth. 鈥淲e鈥檙e starting to get some ideas of how thunderstorm mechanics might work in a hydrogen-dominated atmosphere,鈥� says Brueshaber. 鈥淲e鈥檙e learning that maybe they鈥檙e more alike with Earth than we thought previously.鈥�
Icarus
