Ammonia-water mushballs raining on Jupiter, says new theory

An artist’s concept animation of what it is like in the upper atmosphere of Jupiter. Ammonia-water mushballs could be raining out of violent thunderstorms, just like hailstorms on Earth. Via NASA.

Scientists think that “mushballs” – slushy ammonia-water ice balls – form in Jupiter’s violent storms and fall deep into its atmosphere.
These mushballs may explain why ammonia appears depleted in Jupiter’s upper atmosphere.
A new 3D visualization of Jupiter’s upper atmosphere, using data from Juno, Hubble and Earth-based radio telescopes, supports this theory.

Millions come to EarthSky for night sky news and trusted science.
Your donation keeps us free and accessible for all.

Mushballs on Jupiter?

Jupiter’s outer atmosphere consists of hydrogen and helium with small amounts of other gases like water and ammonia. But the ammonia distribution is not uniform in the upper clouds and appears depleted in some sections. Scientists wondered why the planet’s upper atmosphere isn’t more uniformly mixed. In 2020, a group of researchers proposed a bizarre theory. They said violent thunderstorms formed ice-encrusted ammonia-water slush balls, or mushballs. These mushballs then rained down to lower depths of the atmosphere. On April 15, 2025, researchers at the University of California at Berkeley said new research into Jupiter’s upper atmosphere lends further evidence to this theory.

The researchers published their findings in a peer-reviewed paper in Science Advances on March 28, 2025. They also released a preprint describing a visualization of Jupiter’s upper atmosphere in the arXiv preprint server on April 14, 2025.

Back when the original mushball theory was published, Chris Moeckel, the lead author of this new study, was a graduate student at the University of California at Berkeley. He and his advisor, Imke de Pater, thought that the theory seemed too elaborate to be true.

Moeckel said:

Imke and I both were like: ‘There’s no way in the world this is true.’ 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.

How do ammonia-water mushballs form?

Data from the Juno spacecraft orbiting Jupiter and radio telescopes on Earth have shown there’s an uneven distribution of ammonia in the giant planet’s upper atmosphere.

Why is ammonia missing in parts of Jupiter’s atmosphere? In 2020, Tristan Guillot and colleagues proposed the mushball theory. They suggested that strong updrafts in violent storms carry small ice particles to the cold high reaches of the upper atmosphere. There, the ice quickly mixes with ammonia vapor. Ammonia acts like an antifreeze, converting the ice to a slushy liquid. As the particles rise and fall in the storm, similar to how hailstones grow in thunderstorms on Earth, the ammonia-water mushballs grow larger.

Eventually, the ammonia-water mushballs reach a large enough size – perhaps as large as a softball – and can no longer stay aloft. Then they rain down to much lower sections of the upper atmosphere. In other words, the ammonia falls deeper into the planet.

Illustration of a thundercloud on Jupiter showing the formation of ammonia-water mushballs. — An illustration of a violent storm on Jupiter that generates mushballs. The formation of mushballs on large gaseous planets is similar to that of hailstones in thunderstorms on Earth. On Jupiter, thunderstorm clouds create mushballs about 40 miles (64 km) beneath the cloud tops. Strong updrafts carry water ice upward. About 14 miles (22.5 km) below the top cloud layer, ammonia acts on the ice like an antifreeze, creating a mushball, a slushy ammonia-water ball coated in water ice. The mushballs keep moving and growing in size until they become too heavy and fall back down. This system moves water and ammonia (green and blue layer) to deeper parts of the upper atmosphere. Image via NASA/ JPL-Caltech/ SwRI/ CNRS.

Visualizing Jupiter’s upper atmosphere

Moeckel and his collaborators created a 3D visualization of Jupiter’s upper atmosphere. They used data from three sources: the Juno spacecraft orbiting Jupiter, the Hubble Space Telescope, and the Very Large Array radio telescopes in New Mexico. Data from Hubble and the Very Large Array are from February 2017 and April 2019, timed with Juno’s close encounter with Jupiter.

Hubble provided data on the cloud tops, while the Very Large Array probed further below the cloud tops. In addition, a microwave radiometer (an instrument that measures microwave radiation) on the Juno spacecraft collected data even deeper in Jupiter’s atmosphere over a smaller area.

The resulting 3D model of Jupiter’s upper atmosphere showed much of the weather was happening at the top 6 miles (10 km) of the upper atmosphere. In addition, most of Jupiter’s weather systems reached just 6 to 12 miles (10 to 20 km) below the visible clouds. (For comparison, the distance from Jupiter’s outer atmosphere to the center of the planet is 43,500 miles [70,000 km].)

A complex figure, colored red and blue, showing three weather phenomena on Jupiter. Ammonia-water mushballs are formed in the center feature that illustrate an ammonia plume. — This figure, from the April 14, 2025, preprint, shows a 3D cross-section of weather features in Jupiter’s upper atmosphere. The data are from Juno, Hubble and the Very Large Array. Blue features represent higher levels of ammonia, while red shows depleted levels of the gas. The left feature illustrates how weather systems in Jupiter’s upper atmosphere are generally quite shallow. The center feature shows rising plumes of ammonia, and the right feature shows hurricane-like vortices. Mushballs form where there are ammonia plumes (center feature). Image via Chris Moeckel/ UC Berkeley.

Mushballs punch through to deeper layers

Moeckel said:

Every time you look at Jupiter, it’s mostly just surface level. It’s shallow, but a few things – vortices and these big storms – can punch through.

These “punch through” weather systems on Jupiter are hurricane-like vortices, hotspots linked to ammonia-rich plumes that encircle the planet, and large storms that generate lightning and mushballs. They affect the composition of Jupiter’s outer atmosphere.

He continued:

The mushball journey essentially starts about 50 to 60 kilometers [31 to 37 miles] 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 [62 miles] into the planet, where they start to evaporate and deposit material down there. 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.

He added that unique radio data from Juno convinced him that the ammonia-water mushballs theory was in fact playing out in Jupiter’s atmosphere:

There was a small spot under the cloud that either looked like cooling, that is, melting ice, or an ammonia enhancement, that is, melting and release of ammonia. It was the fact that either explanation was only possible with mushballs that eventually convinced me.

Half a disk with bands of heavily textured clouds in bands of reddish-brown, blue and white. — An image of Jupiter by the Juno spacecraft on September 7, 2023, during a close fly-by. Ammonia in Jupiter’s clouds is not uniform in the upper atmosphere. Scientists have found evidence that it rains out of the clouds as ammonia-water mushballs (ice-encrusted ammonia and water sludge balls). Image via NASA/JPL-Caltech/ SwRI/ MSSS/ Tanya Oleksuik. (CC BY NC SA 3.0)

You can’t tell a planet’s composition by its outer atmosphere

Rain and storms mix the vertical layers of planetary atmospheres. For a long time, scientists thought large gas giants like Jupiter had a homogenous atmosphere.

Moeckel noted:

The turbulent cloud tops would lead you to believe that the atmosphere is well mixed. 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.

We’re basically showing that the top of the atmosphere is actually a pretty bad representative of what is inside the planet.

He and his co-author, Imke de Pater, think ammonia-water mushballs are also raining down on Saturn, Uranus and Neptune. In addition, mushballs could be falling in many large gaseous exoplanets, that is, planets outside our solar system.

Bottom line: Scientists have found evidence that ice-encrusted ammonia-water slush balls are raining down on Jupiter. This could explain why some parts of its upper atmosphere are deficient in ammonia.

Source: Tempests in the troposphere: Mapping the impact of giant storms on Jupiter’s deep atmosphere

Source: The Tropical Atmosphere of Jupiter – Shallow Weather, Deep Plumes, and Vortices

Via University of California Berkeley

Read more: Citizen scientists study Jupiter’s storms using Juno images

#Ammoniawater #mushballs #raining #Jupiter #theory