Extraterrestrial Superstorms

Gas giants host storms that dwarf anything on Earth—planet-sized vortices driven by internal heat and atmospheric chemistry rather than ocean evaporation. The largest and most famous example, Jupiter’s Great Red Spot, can persist for centuries, with winds that remain strong even as the storm’s shape and size appear to change. Understanding why these anti-cyclonic systems last so long—and whether they are beginning to fade—has become a central goal for planetary science.

On Earth, hurricanes, cyclones, and typhoons share a common engine: warm, moisture-laden air rises, cools, and condenses, while precipitation and cooler air sink, sustaining a vertical convection cell. The storm’s rotation comes from the Coriolis force acting on air moving over a rotating planet, producing cyclonic rotation—clockwise in the Southern Hemisphere and counterclockwise in the Northern. Hurricanes weaken when they lose access to warm ocean water, because convection and moisture supply stall. Low-pressure cores tend to support longevity by drawing in moist air, while high-pressure cores push air outward, depleting moisture and shortening the storm’s life.

Gas giant storms follow a different rulebook. They are often anti-cyclonic, high-pressure systems, powered largely by the slow gravitational contraction of the planet rather than solar heating of a surface ocean. As Jupiter and other gas giants shrink over time, gravitational potential energy converts into heat. That heat drives convection: rising gas cools, and—unlike Earth’s relatively narrow condensation chemistry—gas giants span wide temperature and pressure ranges that allow many molecular species to condense. Phase changes release latent heat, lifting storms higher through the troposphere, which can extend roughly 100 miles into a gas giant’s interior. Strong storms can even breach into the stratosphere, warming upper layers; in Jupiter’s case, activity associated with the Great Red Spot warms the upper atmosphere to about 1,600 Kelvin.

The longevity puzzle remains unsolved, but several factors appear to help. The Great Red Spot likely benefits from a near-continuous internal heat supply, abundant condensable molecules, frequent “cannibalization” of smaller storms, and a surrounding environment shaped by jet streams moving in opposite directions at roughly 300–400 miles per hour. Even so, recent observations suggest the storm may be changing. Its size has shrunk dramatically since the 1800s—from about 37,000 kilometers across (roughly three Earths wide) to about 16,350 kilometers (about 1.3 Earths) as of April of this year. It is also becoming more circular, while wind speeds appear not to have dropped.

To probe the structure behind those changes, NASA’s Juno mission—launched in 2011—has been flying close to Jupiter, coming within about 3,400 kilometers of the cloud tops and ultimately designed to crash into them to protect potentially life-bearing moons like Europa. Juno carries eight instruments, including a radiometer, imaging spectrograph, magnetometer, and JunoCam. Every 53 days, it dips into Jupiter’s radiation belt and collects high-cadence imagery during a two-hour pole-to-pole transit, snapping pictures every 60 seconds to measure cloud heights and horizontal drift.

JunoCam images processed with help from citizen scientists have revealed new internal behavior within the Great Red Spot: more “storms within storms,” a shift from long streaks to smaller eddies, and a calm central region reminiscent of a hurricane’s eye. The emerging picture links increased turbulence—acting like friction that saps rotational energy—to the spot’s shrinking and circularization. With dozens more flybys still ahead, scientists are now working through a growing dataset to determine whether the Great Red Spot is merely evolving or truly entering a long decline.