Unified model explains extreme jet streams on all giant planets

One of the most notable properties of the giant planets in our solar system—Jupiter, Saturn, Uranus and Neptune—are 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 Leiden Observatory and SRON, can explain the winds on all the giant planets using one model.

So-called fast rotating convection in the atmospheres of the giant planets can play a crucial role in driving both east and westward jet streams. This is what a team of astronomers led by postdoctoral researcher Keren Duer-Milner from Leiden Observatory and SRON has found. The research has been published in the journal Science Advances.

Using global circulation models, the team found that differences in atmospheric depth can produce the eastward jets on Jupiter and Saturn and the westward jets on Uranus and Neptune. The system shows a so-called bifurcation: Under the same conditions, the atmosphere can settle into one of two stable states—either eastward or westward equatorial jets—establishing a direct link between jet direction and atmospheric depth.

Fastest winds in the solar system

For decades, scientists were puzzled by the mechanism that drives the super-fast winds on the giant planets, with speeds between 500 and 2,000 km/h. The jet streams are the fastest winds observed in the solar system and greatly exceed typical wind speeds on Earth.

Especially the fact that Jupiter and Saturn have eastward winds, while the jets on Uranus and Neptune blow westward, was enigmatic. The main factors that could influence streams on these planets are thought to be similar. The planets receive little sunlight, they have a moderate internal heating source and a fast rotation. There are no known forces that could explain the different direction of the winds. Until now, the different direction of jet winds was thought to come from different mechanisms driving them.

Now, Duer-Milner and colleagues found that fast rotating convection cells on the equator can act as a “conveyor belt” on the surface, driving the jet streams both eastward and westward on different planets. Convection is the process that by circulation can transport heat within an atmosphere or liquid. It is believed to be the main process by which heat from the inside of the gas planets is transported to the surface.

Atmospheres across the galaxy

“We hoped to demonstrate that the mechanism we believe acting in the gas giants Jupiter and Saturn can explain equatorial jets in the ice giants Uranus and Neptune as well,” says Duer-Milner. “We’re excited because we’ve finally found a simple, elegant explanation for a complex phenomenon.” The scientists are now using measurements from the Juno spacecraft to find evidence that the proposed mechanism exists within Jupiter’s atmosphere.

Duer-Milner hopes 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 throughout the universe,” she says.