In a groundbreaking discovery that reshapes our understanding of the giant planets within our solar system and beyond, planetary scientists at the University of California, Berkeley, have unveiled compelling evidence of unusual hailstorms on Jupiter—hailstones unlike anything seen on Earth, composed of ammonia and water slush encrusted within shells of water ice. Dubbed “mushballs,” these icy conglomerates are formed during Jupiter’s powerful storms and plunge deep into the planet’s atmosphere, challenging longstanding assumptions about atmospheric composition and mixing on gas giants.
For decades, astronomers have relied on the assumption that the atmospheres of giant planets such as Jupiter are well-mixed environments. However, recent observations, particularly from NASA’s Juno mission combined with sophisticated radio telescope data, have painted a far more complex picture. The new research reveals that what occurs in Jupiter’s upper atmosphere is only the tip of the iceberg. Most weather activity is shallow, limited to the upper 10 to 20 kilometers beneath the visible cloud decks, while certain dynamic events like massive storms and tornado-like vortices penetrate far deeper, influencing atmospheric chemistry in ways never before fully understood.
The idea of mushballs originated in 2020 as a theoretical solution to the perplexing nonuniform distribution of ammonia gas detected in Jupiter’s troposphere, a region just below the cloud tops. Ammonia is a critical tracer molecule whose presence and abundance typically help scientists infer atmospheric dynamics and chemical processes. Initial skepticism greeted the theory — it required a highly specific set of atmospheric conditions and complex storm behaviors that seemed almost too intricate to exist naturally. Yet, after years of rigorous study and failing to disprove the concept, researchers including Ph.D. graduate Chris Moeckel and his advisor Imke de Pater, professor emerita of astronomy and planetary science at UC Berkeley, embraced the new model, supported by sophisticated 3D visualizations of Jupiter’s atmosphere.
The visualizations depict a north-south swath crossing Jupiter’s equator revealing the depth and character of storms, with blue and red colors indicating regions of higher and lower than normal ammonia concentrations, respectively. These images uncover that while much of Jupiter’s colorful banded atmosphere is governed by shallow weather systems, powerful storms, such as those creating mushballs, reach deep enough to disrupt the expected homogeneity by transporting ammonia downward into the planet’s interior. This overturns previous assumptions that the atmosphere’s upper layers adequately represented the planet’s overall chemical makeup.
Unlike Earth, where raindrops fall until they meet a solid surface, Jupiter lacks a conventional surface; its atmosphere transitions gradually into its interior dense fluid phases. This raises a fundamental question that has fascinated planetary scientists for decades: To what depth do precipitation phenomena like rain and hail extend within the immense gaseous envelope? Answering this has implications not only for Jupiter but for interpreting atmospheric phenomena on all gas and ice giants, including distant exoplanets whose atmospheres we can probe only through limited remote sensing.
What makes mushballs particularly intriguing is their formation and dynamic behavior. According to the theory put forth by planetary scientist Tristan Guillot and supported by new data, intense storm updrafts on Jupiter—reaching nearly 100 meters per second—carry tiny frozen water droplets tens of kilometers above the cloud deck. At these extreme altitudes, the presence of ammonia vapor acts as an antifreeze, melting the frozen particles into slushy, semi-liquid mushballs. These grow as they cycle upward and downward within storm cells, becoming softball-sized hailstones capable of pulling vast quantities of ammonia and water downwards as they fall, far beyond the depths previously thought possible.
These mushballs, carrying ammonia-water mixtures in roughly a 3:1 ratio, explain the puzzling observation that ammonia is significantly depleted in Jupiter’s upper atmosphere at depths approaching 150 kilometers. Traditional models could not account for such deep, lasting deficiencies without invoking a mechanism like heavy precipitation that physically removes ammonia from the upper layers. The mushball hypothesis bridges this gap elegantly, describing a weather-driven vertical conveyor that effectively “unmixes” Jupiter’s atmosphere, sequestering ammonia deep inside the planet where it becomes nearly invisible to conventional observation methods.
The groundbreaking 3D atmospheric tomography developed for this research was vital in confirming this complex weather-driven system. By integrating data from NASA’s Juno spacecraft, the Hubble Space Telescope’s visible imagery, and the Very Large Array (VLA) radio observations from New Mexico, the scientists reconstructed a comprehensive picture of Jupiter’s troposphere. Their method transformed the radio signals into volumetric renderings, exposing the stratification of storms and the depths to which they extend. This approach uncovered that while layers near the visible cloud deck churn vigorously, a deeper atmosphere lies relatively stable but is occasionally punctured by deep-reaching storms responsible for mushball formation.
One of the most striking confirmations came from the unique radio signatures detected beneath storm clouds. These signatures matched neither simple ammonia enhancements nor melting ice alone but were consistent only with ammonia-rich melting mushballs in mid-flight. The findings also counter the expectation that precipitation such as water droplets or ammonia snow would fully explain the observations, lending powerful observational support to the previously speculative mushball model.
Interestingly, the discovery also highlights a broader issue in planetary science: the often-limited availability of fully calibrated observational data from space missions. Moeckel’s team had to painstakingly reconstruct much of Juno’s data processing independently due to delays in public data release. Ultimately, their efforts to create openly accessible calibration tools and data sets promise to accelerate independent research and collaborative advancement in the field, democratizing the exploration of planetary atmospheres.
This revelation about Jovian weather systems has profound implications beyond our solar system. Since many exoplanets discovered to date are gas giants showing atmospheric signatures via transits or direct imaging, understanding that upper atmosphere readings may not reflect internal compositions challenges how scientists interpret exoplanetary atmospheres and their potential for habitability or formation history. “What we’re really seeing is that the upper atmosphere is a poor proxy for the planet’s interior,” Moeckel noted, emphasizing that atmospheric storms and precipitation processes cause significant chemical stratification.
In the broader context, the data and modeling emerging from this research will steer future missions and telescopic observations aimed at the outer planets. The role of water condensation layers as gatekeepers controlling storm dynamics, and how only the most powerful atmospheric disturbances can penetrate these, become crucial knowledge as humanity prepares for the next generation of exploratory spacecraft and more sensitive telescopes like the James Webb Space Telescope.
Ultimately, these insights unify observations, theory, and simulation to illuminate the spectacular and alien meteorology of the largest planet in our solar system. From the exotic mushball hailstorms plunging kilometers below cloud tops to the vast and colorful swirling bands shaped by shallow and deep dynamics alike, Jupiter’s atmosphere is an ever-evolving laboratory for understanding the physics of atmospheric circulation and chemical processes on a scale utterly unlike anything on Earth.
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Subject of Research: Jupiter’s atmospheric dynamics and deep storm systems involving ammonia-water mushballs
Article Title: Tempests in the Troposphere: Mapping the Impact of Giant Storms on Jupiter’s Deep Atmosphere
News Publication Date: 28-Mar-2025
Web References:
– DOI: 10.1126/sciadv.ado9779
– Preprint: https://arxiv.org/abs/2504.09943
References: Science Advances journal article, NASA’s Juno mission data
Image Credits: Chris Moeckel, UC Berkeley
Keywords
Jupiter, mushballs, ammonia, troposphere, planetary storms, gas giants, atmospheric dynamics, Juno mission, radio tomography, exoplanets, atmospheric chemistry, water condensation
