Since entering Jupiter’s orbit in 2016, NASA’s Juno spacecraft has completed 37 flybys of the giant planet, shedding light on the unseen processes raging beneath its clouds with each pass.
Now, scientists studying data taken by the spacecraft’s microwave radiometer (MWR) and NASA’s Earth-based Deep Space Network tracking antenna have made new insights into the structure of one of Jupiter’s most iconic features - the Great Red Spot. With its bright crimson hue and diameter wider than the Earth, this enigmatic anticyclone has captured the imagination of astronomers since its discovery two centuries ago.
Data from the MWR shows that cyclones within the giant planet’s atmosphere, large-scale air masses that rotate anticlockwise around a centre of low atmospheric pressure in the northern hemisphere, are warmer near the top and colder near the bottom. While anticyclones, such as the Great Red Spot, rotate in the opposite direction and are colder at the top but warmer at the bottom.
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The findings also indicate these storms are far taller than expected, with some extending 100km below the cloud tops and others, including the Great Red Spot, extending over 350km.
“Previously, Juno surprised us with hints that phenomena in Jupiter’s atmosphere went deeper than expected,” said Dr Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. “Now, we’re starting to put all these individual pieces together and getting our first real understanding of how Jupiter’s beautiful and violent atmosphere works – in 3D.”
A second team of researchers then used data on Jupiter’s gravity field recorded by NASA’s Earth-based Deep Space Network tracking antenna to produce a second estimate of the Great Red Spot’s depth. As the Great Red Spot is so large, Juno experiences small gravitational tugs as it flies over it.
By measuring tiny changes in Juno’s velocity as small as 0.01 millimetres per second due to the changes in gravitational pull, the team were able to produce an estimate of the Great Red Spot’s depth of around 500km. When combined with the MWR data this suggests the anticyclone is between 350 and 500km deep.
“The precision required to get the Great Red Spot’s gravity during the July 2019 flyby is staggering,” said lead author Marzia Parisi, a Juno scientist from NASA’s Jet Propulsion Laboratory in southern California. “Being able to complement MWR’s finding on the depth gives us great confidence that future gravity experiments at Jupiter will yield equally intriguing results.”