The weather gets a little wild and weird on Jupiter. How wild?
Spacecraft instruments have measured strong winds, tracked fierce lightning, and found huge methane plume storms rising from deep beneath the clouds.
How weird? Think: mushballs raining down like hailstones. They’re made of ammonia and water encased in a water ice shell.
According to planetary scientists, these mushballs plunge through the Jovian atmosphere. What’s more, they probably form on the other gas and ice giants, too.
According to planetary scientist Chris Moeckel and his former advisor Imke de Pater at UC Berkeley, the proof for these strange Jovian slushies came from 3D visualizations of the Jovian atmosphere.
You can’t tell they’re there just by looking at the clouds, however.
You have to find a way to peer into the atmosphere and measure the chemical fingerprints of the gases it contains. In 2020, data from the Juno mission and observations by radio telescopes on Earth uncovered strange “nonuniformities” in ammonia gas distribution around the planet.
In other words, it isn’t distributed evenly throughout the atmosphere.
The Juno data in particular showed that ammonia isn’t just poorly distributed – it’s actually depleted to atmospheric depths of about 150 kilometers, according to de Pater.
“Juno really shows that ammonia is depleted at all latitudes down to about 150 km (93 miles), which is really odd,” said de Pater, who discovered 10 years ago that ammonia was depleted down to about 50 km (31 miles). “That’s what Chris is trying to explain with his storm systems going much deeper than we expected.”
Follow the Ammonia Trail
To explain that missing ammonia, another scientist named Tristan Guillot proposed a wild idea: that strong updrafts during storms on Jupiter can lift ice particles high above the clouds.
There, the ice mixes with ammonia vapor, which melts the ice into a slush. Just like on Earth, as the ice balls rise and fall, they grow. Eventually, these softball-sized mushballs fall back into the atmosphere, taking the ammonia with them. This helps explain why ammonia appears to be missing from the upper atmosphere: it’s being dragged down and hidden deep inside the planet, where it leaves faint signatures to be observed with radio telescopes.
To Moeckel and others, that idea seemed like an “out there” explanation. “Imke and I both were like, ‘There’s no way in the world this is true,’” said Moeckel. “So many things have to come together to actually explain this, it seems so exotic. I basically spent three years trying to prove this wrong. And I couldn’t prove it wrong.”
Jovian Conditions Conducive to Mushballs
It turns out that conditions in Jupiter’s atmosphere could support the formation of mushballs. That atmosphere is mostly hydrogen and helium, inhabited by clouds in its upper layers. Beneath the clouds and upper atmosphere lies a deeper layer of fluid metallic hydrogen. A rocky inner core lives deep inside the planet.
The atmosphere contains smaller amounts of ammonia molecules and water vapor, which rise and freeze into droplets. On Earth, droplets of water fall onto the surface as rain or hail. However, Jupiter has no surface until you get to the core. So, if those droplets do fall, how far down do they go? How big do they get?
This is where the mushballs come in. First, scientists began trying to figure out the strange distribution of ammonia in particular. There were proposals that water and ammonia ice get locked up in hailstones.
However, nobody could quite explain how to form them heavy enough to fall hundreds of kilometers through Jupiter’s messy atmosphere. That’s when Guillot made his proposal for the growth of slushy hailstones.
Making a 3D Model
To understand the weather conditions and the possible formation of those weird mushballs, Moeckel began working on a different approach based on the observational data.
“I essentially developed a tomography method that takes the radio observations and turns them into a three-dimensional rendering of that part of the atmosphere that is seen by Juno,” Moeckel said.
Moeckel’s 3D picture of Jupiter’s troposphere shows that the majority of the weather systems on Jupiter really are shallow.
Most extend down perhaps only 10 to 20 kilometers below the visible clouds. Most of the colorful, swirling patterns in the bands encircling the planet are part of that shallow contingent of clouds.
Some weather, however, emerges much deeper in the troposphere, redistributing ammonia and water and essentially unmixing what was long thought to be a uniform atmosphere. The three types of weather events responsible are hurricane-like vortices, hotspots coupled to ammonia-rich plumes that wrap around the planet in a wave-like structure, and large storms that generate mushballs and lightning.
Tripping with a Mushball
“The mushball journey essentially starts about 50 to 60 kilometers below the cloud deck as water droplets. The water droplets get rapidly lofted all the way to the top of the cloud deck, where they freeze out and then fall over a hundred kilometers into the planet, where they start to evaporate and deposit material down there,” Moeckel said.
“And so you have, essentially, this weird system that gets triggered far below the cloud deck, goes all the way to the top of the atmosphere, and then sinks deep into the planet.”
Unique signatures in the Juno radio data for one storm cloud provided an important clue to the mushball formation. “There was a small spot under a cloud that either looked like cooling, that is, melting ice, or an ammonia enhancement, that is, melting and release of ammonia,” Moeckel said. “It was the fact that either explanation was only possible with mushballs that eventually convinced me.”
What About Other Planets?
The 3D model and explanations of mushballs on Jupiter offer a more complete look at the complicated dynamics of the Jovian atmosphere.
Interestingly, it’s very likely that similar conditions for mushball creation could exist at the other gas and ice giants of the solar system.
If so, that would give planetary scientists much more insight into the interiors of those worlds as well as the activities going on in their atmospheres.
In an age of exoplanet research, it’s also likely that researchers can use Moeckel’s tools to extrapolate what they’ve seen at Jupiter to similar-type worlds around other stars.
Since they can see only the upper atmospheres of distant worlds, the ability to interpret chemical signatures in those atmospheres using radio and other observations is important.
Written by Carolyn Collins Petersen/Universe Today.
