Left shows an image of Jupiter’s clouds and swirling wind patterns, with corresponding computer simulations shown on the right. Credit: NASA/JPL/University of Alberta/MPS
Computer simulations have offered an explanation as to the location and cause of Jupiter’s whirlwinds, including the reason why they rotate in the opposite direction to those found on Earth.
The study found that Jupiter’s whirlwinds are caused by gas flows that rise from deep under the planet’s surface.
Simulations have shown the winds occurring in wide bands north and south of Jupiter’s equator for the first time, in the area where the Great Red Spot is located.
Jupiter’s Great Red Spot is a massive anticyclone that measures up to twice Earth’s diameter and is about 350 years old.
The term ‘anticyclone’ refers to the fact that Earth’s storms rotate anticlockwise in the northern hemisphere and clockwise in the south, while Jupiter’s whirlwinds spin the other way.
"Our high-resolution computer simulation now shows that an interaction between the movements in the deep interior of the planet and an outer stable layer is crucial," says Johannes Wicht from the Max Planck Institute for Solar Research (MPS), which worked with the University of Alberta in Canada on the simulations.
Jupiter consists mostly of hydrogen of helium; a mixture that becomes metallic and electrically conductive deep within the planet due to the high pressure caused by the surface layers.
Closer to the surface, these gases exist in their non-metallic state in a more stable, outer layer, where the whirlwinds occur.
Simulations depicted this stable layer for the first time, showing just the top 7,000 kilometres of the non-metallic region.
Further inside the core of Jupiter, in the electrically conductive region, immense heat causes gas to rise upwards, but the stable layers closer to the surface provide a sort of barrier.
"Only when the buoyancy of the gas package is strong enough, it can penetrate into this layer and spreads out horizontally. Under the influence of planetary rotation, the horizontal movement is swirled, just as is observed for hurricanes on Earth”, says Wicht.
When this gas then cools, it sinks again.
The various rotational and horizontal motions that occur as this process happens in the simulations correspond to actual observations of the planet’s surface.
On Earth, cyclones are formed as a result of air converging and rising, while on Jupiter these vortices form when the rising gas is pulled apart in the upper atmosphere.
This solution explains why the cyclones on Jupiter swirl the opposite way from those found on Earth.
"Simulating the conditions in Jupiter’s atmosphere is tricky since many properties of this region are not well known," says MPS scientist Thomas Gastine.
The researchers are still unable to define exactly what causes Jupiter’s Great Red Spot using these simulations, however.
"We are just beginning to understand Jupiter’s weather phenomena", Wicht says.
"In addition to its size and durability, the Red Spot has other special features such as its characteristic colour.
Additional processes seem to be involved here that we don’t yet comprehend.”