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Caltech researchers have developed a new simulation of the hydrological cycle on Jupiter, modeling how water vapor condenses into clouds and falls as rain throughout the giant planet's swirled, turbulent atmosphere. The research shows that Jupiter's water is not uniformly distributed, giving missions like NASA's Juno orbiter important guidance about where to look for water on the planet.

Jupiter was considered the first planet in our solar system to form, and its massive gravitational influence shaped the orbital architecture of Earth and the other planets in the solar system. Understanding how much water Jupiter has—and where to look for it—gives clues to how water arrived on Earth, which is still an open question in planetary science.

The research is in Proceedings of the National Academy of Sciences. The study's first author is Huazhi Ge, a postdoctoral scholar in the group of Andrew P. Ingersoll, professor of planetary science, emeritus.

"While we are focusing on Jupiter, ultimately we are trying to create a theory about water and atmospheric dynamics that can broadly be applied to other planets, including exoplanets," Ge says.

Jupiter's swirled appearance results from its atmospheric dynamics, which—while visually striking—make it difficult to determine the abundances of chemical species such as water and metals. The Galileo mission first detected water on Jupiter near its equator in the 1990s, but it remained uncertain whether that water was distributed evenly across the giant planet.

The new model accounts for Jupiter's rapid rotation—one full rotation (one day) on Jupiter takes only about 10 Earth hours. This fast rotation causes the turbulent stripes visible in Jupiter's atmosphere. The new model suggests that this turbulence in the subtropic and mid-latitudes leads to rain that draws water deeper beneath the cloud layer, making the planet's lower atmosphere more humid tens of kilometers beneath the clouds.

Jupiter is different from Earth in many ways, so modeling its atmospheric dynamics—and then comparing those models with observations—leads to a better understanding of a diverse range of planets more broadly. Next, the team plans to create a more global model, expanding past the mid-latitudes. Ideally, the theory can be applied to other gas giants like Uranus and Neptune that also have nonuniform distributions of chemical species like methane rather than water.