NASA’s Juno spacecraft arrived in orbit around Jupiter in 2016. Its primary mission was to peek below the dense gas clouds that comprise the giant. But it has just spotted a whole lot of lighting in the upper atmosphere. That, and mushballs.
Juno, as well as several other NASA missions, had previously revealed that lightning occurs in Jupiter’s lower atmospheres, where water clouds exist. But thanks to its ongoing mission and the use of a camera designed to pick up dim light, the craft has just detected copious amounts of shallow lighting on the planet’s dark side, close to its outer atmosphere where ammonia plays a significant role.
“On the night side of Jupiter, you see fairly frequent flashes—as if you were above an active thunderstorm on Earth,” said Jonathan I. Lunine, chair of the Department of Astronomy in the College of Arts and Sciences at Cornell University. “You get these tall columns and anvils of clouds, and the lightning is going continuously.”
The ammonia works as a kind of antifreeze, say the researchers in a paper published in the journal Nature, dissolving particles of ice into liquid water, despite the cold temperatures (approximately -150°F) found in Jupiter’s upper atmosphere. This mixture of ammonia and water falls toward the planet’s core, where it collides with ice particles, creating the charge that sparks the lightning.
“Shallow lightning hadn’t really been expected and indicates that there’s an unexpected process causing it,” said co-author and doctoral candidate, Youry Aglyamov. “It’s one more way in which Juno’s observations show a much more complex atmosphere of Jupiter than had been predicted. We know enough now to ask the right questions about processes going on there, but as Juno shows, we’re in a stage where every answer also tends to multiply the questions.”
Ammonia has also been found to play a role in creating “mushballs,” a kind of wet Jovian hail that has likely led to the depletion of ammonia in the planet’s upper atmosphere as found by Juno. Reporting in a separate paper, the researchers state the following about the ammonia slurry:
During Jupiter’s violent storms, hailstones form from this liquid, similar to the process in terrestrial storms where hail forms in the presence of supercooled liquid water. Growth of the hailstones creates a slush‐like substance surrounded by a layer of ice, and these “mushballs” fall, evaporate, and continue sinking further in the planet’s deep atmosphere, creating both ammonia depletion and variability, potentially explaining the Juno observations.
Juno’s mission was extended in June of 2018 because its orbit had to be adjusted due to concerns about valves on its fuel system that caused its orbit to jump to 53 days versus 14 days. It is now scheduled to plunge into the Jovian atmosphere in July 2021. During that time, scientists are hoping to discover even more perception-shifting discoveries about the gas giant.
“Giant planets, in general, are a fundamentally different kind of world from Earth and other terrestrial planets,” said Aglyamov. “There are hydrogen seas transitioning gradually into skies stacked with cloud decks, weather systems the size of the Earth, and who-knows-what in the interior.”