Mapping Jupiter’s Skies: A Full-Atmosphere Model

Antonín Knížek and colleagues present a new model of Jupiter’s atmosphere that spans from the deep interior up through the high stratosphere. Jupiter, the largest planet in the Solar System, is made mostly of hydrogen and helium, but also contains water, methane, ammonia, hydrogen sulfide, and nitrogen. Past missions such as Voyager, Galileo, and Juno have provided snapshots of the atmosphere, but existing models usually focused on only one region or one type of chemistry. This work is the first to combine thermochemistry, kinetics, and photochemistry into a single model, while also including sulfur chemistry across the entire vertical extent of Jupiter’s atmosphere.

Building the Model

The team used a one-dimensional computer code called ARGO, which accounts for chemical reactions, atmospheric mixing, and the effects of sunlight. They combined pressure and temperature data from Galileo and other studies and set the lower boundary of the model at 1400 K, a temperature where equilibrium chemistry is expected. To make the model realistic, they updated reaction rates, added chemistry for ammonium hydrosulfide (NH4SH), and included condensation and evaporation of key species like ammonia and hydrogen sulfide. They then compared their results with earlier models and observations to ensure accuracy.

Gas and Cloud Chemistry

The model reproduces the expected behavior of major gases like methane, carbon monoxide, and hydrocarbons. It predicts that both ammonia (NH3) and ammonium hydrosulfide condense to form a cloud layer between 0.1 and 1 bar, consistent with the orange-brown clouds seen on Jupiter. This mixed NH3–NH4SH layer is important because it locks sulfur deep below the cloud tops, while ammonia reappears higher up due to sunlight-driven chemistry. The model also matches observed methane distributions, though some hydrocarbons such as acetylene (C2H2) appear in slightly different amounts than previous studies suggested.

Deep Troposphere and Nitrogen Quenching

In the deep atmosphere, the chemistry is dominated by equilibrium, but as gases rise, reactions slow down and molecules become “quenched,” meaning their abundances freeze at certain levels. For nitrogen, the model predicts a nearly constant N2 mixing ratio of about 11 ppm up to 10⁻⁶ bar, much higher than what equilibrium would suggest. This finding bridges gaps between earlier equilibrium models and upper-atmosphere studies and helps explain Jupiter’s observed nitrogen chemistry.

Hydrogen Cyanide

One of the most striking results concerns hydrogen cyanide (HCN), a molecule tied to nitrogen chemistry and even prebiotic processes. HCN has been observed on Jupiter before, but its origin was uncertain. The new model finds a region in the stratosphere, between 10⁻⁶ and 10⁻⁷ bar, where HCN forms through radical chemistry involving sunlight. At 2.9×10⁻⁷ bar, the predicted abundance peaks at 33 parts per billion, a value within reach of future telescopic measurements. This is a testable prediction that could confirm the model’s accuracy and improve our understanding of how disequilibrium chemistry shapes Jupiter’s atmosphere.

Conclusion

Knížek and colleagues successfully bring together different layers of Jupiter’s atmosphere into a unified model. Their work not only matches many existing observations but also makes new predictions, particularly about cloud formation and the production of hydrogen cyanide. By capturing both equilibrium and disequilibrium processes, the model provides a framework that can guide future missions like JUICE and upcoming telescope studies. It is a step toward connecting what we see at the cloud tops with the hidden processes deep below.

Source: Knížek