Jupiter is a planet of storms, but also a planet of mysteries. How can an expanse of the gas giant that is swirling with cyclones also be a desert?
Expect anything from a planet famous (or infamous) for things like its Great Red Spot and a strange, stormy pentagon that could pass for a formation of UFOs. Jupiter’s “hot spots” (first glimpsed by NASA’s Galileo probe) were an enigma that have stayed in the dark until now. Now its Juno probe has had another look. They were previously thought to be local deserts. What Juno beamed back suggests that these hot spots, which glow deceptively bright in the infrared, may not be that different from the rest of Jupiter—at least the part of Jupiter they exist in. That entire region of the planet is a cosmic desert.
Turned out Galileo messed up without even knowing it. Because it plunged into one of the hot spots in the northern equatorial region of Jupiter and found how dry and windy it was, astronomers back on Earth automatically assumed each hot spot to be its own localized desert. They go much deeper and further than that, if you ask Juno co-investigator Tristan Guillot.
“We’re seeing that the entire area has low ammonia abundance and realizing that the hot spots may be just clearing in the clouds,” Guillot told SYFY WIRE. “The storms we see on the JunoCam images must have transported both ammonia and water deep down, not only where the hot spots are, but everywhere around these latitudes.”
Juno has revealed that the hot spots have something to do with cracks in Jupiter’s thick clouds, which could allow the probe to peer into the depths of the Jovian atmosphere where it is hotter and drier than anywhere else. Something else Juno saw was that a phenomenon known as shallow lightning was being powered by these desert storms. For lightning to form, there needs to be a liquid in the atmosphere to enlarge particles and transfer charge. Shallow lightning is so weird because it can occur at atmospheric levels that are too cold to keep water in its liquid state. This is where ammonia comes in. If you mix water and ammonia, you can keep water liquid so lightning can ignite even in such a deep freeze.
It only gets stranger from here. Juno’s microwave instrument can no longer see water and ammonia when they join forces. Not only that, but they also produce alien hailstones not-so-scientifically called mushballs. Gargantuan storms that arise from water condensing much deeper in the atmosphere give rise to mushball formation. Shallow lightning literally illuminates where these storms are forming, something that could eventually help with the understanding of how heat moves around inside the planet. If humans could actually live on Jupiter, shallow lightning would be a dread sign of incoming mushballs.
“Mushballs reveal that Jupiter’s atmosphere is quite different than expected,” said Guillot. “Instead of being convectively unstable and homogeneously mixed, we now envision the deep atmosphere as stable on average, with an increase in ammonia and water abundances as you’re going deeper.”
When mushballs grow heavy enough, they drop through the atmosphere and leave behind a region almost devoid of ammonia and water. They need to melt and evaporate for the ammonia and water to become gas again and therefore, once more visible to Juno. Guillot sees the behavior of ammonia and water in Jovian storms as analogous to slowly adding milk to water without mixing the liquids. The milk will sink to the bottom of the glass just like water and ammonia sink through Jupiter’s atmosphere during a storm. The difference is that, unlike a glass, Jupiter has no bottom—or surface that we know of. How deep ammonia and water can sink is something that will have to be investigated further. It could hypothetically sink all the way. Nobody knows.
What the Juno team needs to do now is figure out how efficient mushball formation really is, and in what way to apply it to Juno data. The probe has already allowed the Juno team to get an idea of how much water is hiding deep in Jupiter’s atmosphere. For a more precise estimate, they will need to understand how water makes its way to the depths of other regions. Juno may demystify that as it gradually heads towards the north pole of Jupiter, which is thought to have vastly different properties that could tell Guillot and his colleagues even more about bizarre Jovian weather.
“Our research has wide-reaching implications,” he said. “All planets in our solar system, as well as exoplanets, have atmospheres that are very light. The same process could occur when elements condense in these atmospheres. Understanding what is happening in Jupiter will be key when applying our models to interpret exoplanetary spectra soon to be measured by the James Webb Space Telescope.”