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Jupiter south pole, seen by Juno
This image shows Jupiter’s south pole, as seen by NASA’s Juno spacecraft from an altitude of 32,000 miles. The oval features are cyclones, up to 600 miles in diameter. (NASA / JPL-Caltech / SwRI / MSSS / Betsy Asher Hall / Gervasio Robles)

NASA’s Juno orbiter has been sending back stunning pictures of Jupiter for months, but now the mission’s scientists are sharing their first peer-reviewed findings about the planet’s previously unseen polar storms and powerful magnetic field.

“The results from Juno’s initial close passes of Jupiter are understanding of this gas giant,” the Juno science team, led by principal investigator Scott Bolton of the Southwest Research Institute, reports in the journal Science.

Bolton and his colleagues laid out those results today in a set of papers published by Science and Geophysical Research Letters, and in a NASA teleconference.

Jupiter has been previously studied at close range by NASA’s Pioneer and Voyager probes in the 1970s, and by the Galileo orbiter between 1995 and 2003, but Juno is filling in many of the remaining gaps in scientists’ picture of the planet.

Because of its highly elliptical, pole-to-pole orbit, Juno can track the chaotic storms at Jupiter’s poles that earlier observing campaigns have missed.

“They don’t look anything like Jupiter as we know it. … It almost looks like meteor craters, but of course it’s all atmosphere, it’s all gas,” Bolton said in a Science podcast. He said the polar storms are unlike the more regular zone-and-belt patterns seen at the planet’s equator. What’s more, the north pole’s storm patterns are unlike the south pole’s storms.

Some of the oval-shaped storms near the north pole spread wider than 850 miles. One roughly circular high-altitude cloud spans more than 4,000 miles. “It’s a towering, almost tornado-like structure,” Bolton said. “It’s a cyclone of some kind, but it’s three-dimensional.”

The science team says the chaotic scene is “fundamentally different” from the views of Saturn’s polar regions that have been captured by the Cassini orbiter.

The polar storms appear to be whipped up by processes similar to the dynamics that drive Earth’s weather, but it’s not yet clear whether they’re as stable as Jupiter’s better-known equatorial storms, such as the Great Red Spot.

Some of Juno’s pictures show white flecks floating above the main cloud deck. “It’s like it’s snowing on Jupiter and we’re seeing how it works,” Bolton said. But this snow probably contains frozen ammonia, he said.

This image from the Juno probe reveals bright high clouds that are about 16 miles across and in some areas appear to form “squall lines.” On Jupiter, clouds this high are almost certainly composed of water and/or ammonia ice. (NASA / JPL-Caltech / SwRI / Gerald Eichstädt / Seán Doran)

Bolton said Juno will continue to track how storms develop over the course of a primary mission that’s due to last more than a year. “We really need the rest of our mission in order to figure out how Jupiter works,” he told journalists during today’s teleconference.

The length of Juno’s mission is expected to be much shorter than Galileo’s eight-year run because the probe comes much closer to Jupiter’s cloud tops – as close as 3,000 miles – and repeatedly passes through its powerful radiation belts.

Juno’s measurements showed that Jupiter’s magnetic field reached a maximum strength of 7.766 gauss – which is more than 10 times as strong as Earth’s magnetic field, and twice as strong as what scientists predicted based on computer modeling.

Jack Connerney, the lead scientist for the mission’s magnetic field investigation at NASA’s Goddard Space Flight Center, said that Jupiter’s magnetic field is stronger in some places and weaker in others. That suggests that the field may be generated by dynamo action close to the surface, and not by action at its core, he said.

Scientists already knew that Jupiter’s magnetic field sparked intense auroras, based on data from Galileo, but Juno’s ultraviolet and infrared imaging capabilities are giving them a much better idea just how intense the auroras can get.

Some of the auroral emissions appear to be caused by magnetic interactions involving Jupiter’s moons, including volcanic Io and ice-covered Europa and Ganymede.

That’s just one example of how Jupiter’s auroras are different from Earth’s.

“On the Earth, the aurorae are largely dictated by the sun,” Bolton said. “It’s the solar wind interaction with Earth’s magnetosphere, or magnetic field, that creates the aurora. Jupiter’s is fundamentally different. … There’s a part of it that’s tied to the solar wind, but a large part of it is tied to Jupiter’s rotation.”

Connerney said the patterns of particle emissions observed by Juno suggest that electrons are being pulled into Jupiter’s magnetic field from below rather than from above, which is the case for Earth’s aurora.

Juno is also starting to get a handle on Jupiter’s internal structure, thanks to the magnetic field measurements as well as readings about its gravity field.

“It looks like there’s a lot of strange deep motions that possibly are going on inside of Jupiter,” Bolton said.

He said the initial observations suggest Jupiter has a “large, fuzzy core” beneath a layer of liquid metallic hydrogen – which is something scientists didn’t expect.

During one close flyby of Jupiter, Juno’s stellar navigation camera captured a view of the constellation Orion with the giant planet’s faint ring of dust in the foreground. “This is the first image of Jupiter’s ring that has ever been collected from the inside of it looking out,” Heidi Becker of NASA’s Jet Propulsion Laboratory said.

Jupiter's main ring
An image captured by the Juno probe’s Stellar Reference Unit shows the faint line of Jupiter’s main ring, 40,000 miles away, with the constellation Orion in the background. The lines of the constellation have been added to indicate the star Betelgeuse as well as the three stars of Orion’s belt. (NASA/ JPL-Caltech / SwRI)

Juno will continue making close flybys of Jupiter every 53 days. The next encounter, on July 11, will feature the probe’s first flight directly over the Great Red Spot.

There’ll be many more scientific papers to come, but Bolton said the initial results have already confirmed a big-picture observation about planets.

“What Juno’s results are showing us is that our ideas of giant planets may be a little bit oversimplified,” he said. “They’re more complex than we thought. The motions that are going on inside are more complicated. It’s possible that they formed differently than our simple ideas. And so it really is changing the most fundamental way that we think how solar systems are formed, and how giant planets work.”

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