Images taken by NASA’s Cassini spacecraft as it flew past Jupiter in 2000 have been used to discover an atmospheric phenomenon known as “Rossby waves” in a jet stream in the gas giant’s southern hemisphere.
The study was conducted by scientists and amateur astronomers led by Amy Simon-Miller at NASA's Goddard Space Flight Center. John Rogers, Jupiter Section Director of the British Astronomical Assocation and one of the authors of the paper explaining the discovery, said that Jupiter's jet streams had always appeared to be "straight and narrow".
Jet streams are rapidly blowing winds that encircle Jupiter, but they are also present on Earth, which allows an analogy to be made between the two planetary atmospheres.
“By comparing this type of interaction in Earth's atmosphere to what happens on a planet as radically different as Jupiter, we can learn a lot about both planets," says Amy Simon-Miller, lead author of the Icarus paper explaining the phenomenon.
The strongest of Earth’s jet streams blow from west to east around the North and South Poles. However, sometimes the jet streams deviate from this circular path, and move north and south. The north and south motion of the jet streams is actually a wave motion called Rossby waves, and they are responsible for bringing cool air to southern latitudes.
The north and south motion of a Rossby wave is seen in this simulation of the jet stream that circles the Earth's North Pole. Credit: NASA/GSFC
Rossby waves were detected in a jet stream in Jupiter’s northern hemisphere around 20 years ago, but until now there had been no evidence of them in the southern hemisphere.
To get to the bottom of this matter, a team of scientists poured over Cassini images, as well as those taken with the Hubble Space Telescope, and years worth of amateur astronomer observations.
By zooming in on a jet stream in Jupiter’s southern hemisphere, they discovered a series of v-shaped dark spots, dubbed “chevrons,” which move along with the wind in a west to east direction. Further along the jet stream, the chevrons start oscillating up and down, similar to what happens on Earth.
"The chevrons in the fast-moving jet stream interact with the slower-moving Rossby wave, and that's when we see the chevrons oscillate," said David Choi from NASA’s Goddard Space Flight Center. The oscillating chevrons thus betray the presence of the Rossby waves.
The chevrons also revealed that they are connected to another type of wave in Jupiter’s atmosphere known as a gravity inertia wave, which are also seen in Earth’s atmosphere. By studying the gravity inertia waves, scientists will be able to delve deeper into Jupiter’s atmosphere than is currently possible with remote sensing.
Also seen in the main image is the transient storm called the South Equatorial Disturbance (SED) which has been monitored since 1999. This storm also influences the chevrons as they move at slower speeds east of the storm.
Jupiter is the largest planet in our solar system and the fifth planet from the Sun, orbiting at a distance of 778 million kilometres (482 million miles). With a diameter of 141,000 kilometres (87,000 miles) it is about 11 times the diameter of Earth and has 1,000 times the volume.
Jupiter is made primarily of hydrogen and helium gas stretching tens of thousands of kilometres towards what is maybe an inner rocky or icy core.
Jupiter is a swirling violent mass of gas with storms raging constantly. The most recognisable of the Jovian storms is the great red spot which is a huge anticyclonic storm measuring 40,000 kilometres (25,000 miles) across and 14,000 kilometres from north to south. The great red spot has been raging for centuries.