In 2020, a group of scientists came up with an explanation for strange inconsistencies in Jupiter’s upper atmosphere. They suggested that ice-encrusted mushballs rain down during intense thunderstorms on the gas giant. At the time, however, the notion of ammonia-packed slushee hailstones seemed too weird to be true, so they spent the next several years trying to prove it wrong.
But Jupiter’s mushballs could not be denied. New research confirmed the bizarre phenomenon not only exists—it could be taking place on all gaseous planets of the solar system.
In the recent finding, reported in the journal Science Advances, planetary scientists at the University of California, Berkeley (UC Berkeley) confirmed that hailstorms of mushballs, accompanied by fierce lightning, occur on Jupiter. The mushballs—slushy orbs of ammonia and water encased in a hard shell of water ice—deliver ammonia to deeper layers of Jupiter, unmixing its atmosphere.
UC Berkeley graduate student Chris Moeckel and astronomy professor Imke de Pater co-authored the study, which is currently under peer review. They admit they initially thought the theory was too elaborate to be true. “Imke and I both were like, ‘There’s no way in the world this is true,’” Moeckel said in a statement. “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.”
Jupiter is known for its stormy weather, featuring cyclones, anticyclones, large storms, and ammonia-rich plumes that engulf the planet. The planet’s atmosphere is primarily made of hydrogen and helium gas with trace amounts of ammonia and water.
Violent storms within Jupiter’s tumultuous atmosphere are generating the mushballs and shallow lightning, according to the new research. These mushballs are created by thunderstorm clouds located around 40 miles (64 kilometers) beneath Jupiter’s cloud tops. The thunderstorm clouds carry water ice all the way up toward extreme altitudes that are sometimes above the visible layer of clouds. Once they’re at the top, ammonia acts like an antifreeze, melting the ice and combining with it, eventually forming a slushy ammonia-water liquid that is then coated with water ice, thus creating a mushball.
The idea of mushballs was first presented as an explanation for a long-held Jovian mystery: why ammonia is missing from parts of Jupiter’s atmosphere. According to the paper, the mushballs rise up through the atmosphere until they become too heavy and fall back down until they evaporate. In doing so, the mushballs redistribute ammonia and water from the upper atmosphere to layers deep below the clouds, creating areas of depleted ammonia that are visible in radio observations of Jupiter.
“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,” Moeckel said. This results in the chemical composition of the cloud tops not necessarily reflecting the composition deeper in Jupiter’s atmosphere.
The researchers behind the study created the first 3D visualization of Jupiter’s upper atmosphere, which confirmed that mushballs do exist. In fact, the slushy hailstorms could exist on other giant planets like Saturn, Uranus, and Neptune.
Using observations from the Juno spacecraft’s Microwave Radiometer, the Very Large Array, and the Hubble Space Telescope, the researchers were able to probe the depth and impact of weather on Jupiter. The 3D visualization showed that, while the majority of the weather systems on Jupiter are shallow, taking place around 6 to 12 miles (10 to 20 kilometers) below the visible cloud deck of the planet, other weather events go much deeper into Jupiter’s stratosphere. “Every time you look at Jupiter, it’s mostly just surface level,” Moeckel said. “It’s shallow, but a few things—vortices and these big storms—can punch through.”
The study concludes that the shallow weather events on Jupiter cannot explain the depletion of ammonia in the deeper parts of Jupiter’s atmosphere. Instead, the interplay of large-scale events, such as plumes and vortices, combined with storm-scale phenomenon, such as the mushball hailstorms, may be responsible for depleting Jupiter’s atmosphere.
Missions sent to Jupiter and other distant planets of the solar system can only see the upper atmospheres, which is “actually a pretty bad representative of what is inside the planet,” Moeckel said. “The turbulent cloud tops would lead you to believe that the atmosphere is well mixed,” he added. “If you look at the top, you see it boiling, and you would assume that the whole pot is boiling. But these findings show that even though the top looks like it’s boiling, below is a layer that really is very steady and sluggish.”