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Juno what? Jupiter's Great Red Spot is much deeper than originally thought

Boffins release treasure trove of findings from NASA probe, including weird cyclones around the poles

Revelations that Jupiter's Great Red Spot is much deeper than believed and details on the planet's famous banded structures below its cloud layer were among the atmospheric insights collected by NASA's Juno probe and published in science journals today.

Juno entered a polar orbit of Jupiter in 2016 and is the first mission that has been able to peek behind the massive gas giant's dense layer of clouds. It has flown by the planet 37 times to date, equipped with, among other measuring instruments, a microwave radiometer (MWR) that collects data on Jupiter's atmospheric structure, movement, and chemical composition up to 342 miles below the top of the clouds.

The studies published in Science and the Journal of Geophysical Research: Planets cover discoveries about the cloud layer's belts and zones, polar cyclones, and the legendary Great Red Spot.

When it comes to Jupiter's famous beauty mark, general assumptions over at least two centuries have been that it was a shallow storm. However, data analyzing microwave and gravity measurements from 12 of the encounters, including two direct overflights of the vortex, now suggest the mysterious storm reaches down over 200 miles (321km+) below the atmosphere's cloud tops.

Additionally, scientists can now say the massive storm's roots plunge past where the water condenses in the atmosphere to form the clouds where sunlight does not reach. The storm does change shape and may be getting smaller.

Another distinctive mark for Jupiter is its belts and zones, the white and red cloud bands wrapping around the planet. These bands have winds that move in alternate directions, thus separating them out. Scientists already knew that these jet streams were up to 2,000 miles (3,200km) deep, but they couldn't quite pick up how they formed. Now, the belief is that ammonia gas that accompanies the jet streams might have something to do with it, thanks to the data from the MWR.

Furthermore, the belts and zones make a distinct transition at about 40 miles (65km) beneath the clouds where they turn into a darker hue that resembles Earth's oceans. Above that transition line, which the boffins dubbed the "jovicline" in a nod to Earth's "thermoclines", the belts are brighter in microwave light than areas surrounding them.

"Belts and zones do persist to pressures of 100 bars or more, but they flip their character at a level which we call the 'jovicline', coinciding with the depths at which water clouds are expected to form and generate a stable layer," wrote researchers.

As for the cyclones that collect around the poles, they've been known to gather in groups of eight at the north and five at the south with an additional cyclone centered at each pole.

Scientists now feel safe saying those shapes are here to stay, thanks to data from the spacecraft's Jovian Infrared Auroral Mapper (JIRAM). While the cyclones are attracted to the poles, they keep each other in check, affecting each other's motion and oscillating about an equilibrium position, likely with deep roots.

"Previously, Juno surprised us with hints that phenomena in Jupiter's atmosphere went deeper than expected," said Juno's principal investigator Scott Bolton. "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."

When Juno is finished with the massive central part of the planet itself, it's due to fly by the gas giant's large moons, Europa and Io, and explore the small rings around the planet. ®

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