A unified model explains extreme jet streams on all giant planets

One of the most remarkable properties of our solar system’s giant planets – Jupiter, Saturn, Uranus and Neptune – is the extreme winds observed around their equators. While some of these planets have eastward equatorial winds, others have a westward jet stream. For the first time, an international team of scientists led by the Leiden Observatory and SRON can explain the winds on all giant planets using a single model.

So-called rapidly rotating convection in the atmospheres of giant planets can play a crucial role in pushing jet streams eastward and westward. This was discovered by a team of astronomers led by postdoctoral researcher Keren Duer-Milner from the Leiden Observatory and SRON. The research was published in the journal Scientific advances.

Using global circulation models, the team found that differences in atmospheric depth can produce eastward jets on Jupiter and Saturn and westward jets on Uranus and Neptune. The system exhibits what is called a bifurcation: under the same conditions, the atmosphere can stabilize in one of two stable states – either eastward or westward equatorial jets – establishing a direct link between jet direction and atmospheric depth.

The fastest winds in the solar system

For decades, scientists have been intrigued by the mechanism that drives the ultra-fast winds on giant planets, with speeds between 500 and 2,000 km/h. Jet streams are the fastest winds observed in the solar system and far exceed typical wind speeds on Earth.

Particularly puzzling was the fact that Jupiter and Saturn have eastward winds, while Uranus and Neptune’s jets blow westward. The main factors that may influence waterways on these planets are thought to be similar. The planets receive little sunlight, they have a moderate internal heat source and a rapid rotation. No known force could explain the different wind directions. Until now, it was thought that the different wind directions of jet planes came from different mechanisms driving them.

Duer-Milner and colleagues found that rapidly rotating convection cells on the equator can act like a “conveyor belt” on the surface, driving jet streams east and west on different planets. Convection is the process that, through circulation, can transport heat into an atmosphere or liquid. This is believed to be the primary process by which heat from the interior of gaseous planets is transported to the surface.

Atmospheres across the galaxy

“We hoped to demonstrate that the mechanism we believe operates in the gas giants Jupiter and Saturn can also explain the equatorial jets in the ice giants Uranus and Neptune,” explains Duer-Milner. “We are delighted because we have finally found a simple and elegant explanation for a complex phenomenon.” Scientists are now using measurements from the Juno spacecraft to find evidence of the proposed mechanism in Jupiter’s atmosphere.

Duer-Milner hopes that their results can also be applied to planets outside our solar system. “Understanding these winds is crucial because it helps us understand the fundamental processes that govern planetary atmospheres, not only in our solar system but across the galaxy. This discovery gives us a new tool for understanding the diversity of planetary atmospheres and climates across the universe,” she says.