NASA’s Juno spacecraft peeked under the clouds of the most iconic weather feature in the solar system, Jupiter’s Great Red Spot, revealing a complex structure deep below the surface.

NASA’s Juno spacecraft has been orbiting Jupiter for roughly a year and a half and has already provided us with many stunning views of the giant planet. But now NASA has revealed an unprecedented view of what’s below the clouds of one of its most distinctive features: the Great Red Spot.

In June 2017 Juno took the best pictures of the swirling storm to date from a distance of just 9,000 kilometers (5,600 miles). During that pass, Juno’s microwave radiometer (MWR) recorded temperature changes deep below the surface of Jupiter’s long-lasting storm. Juno co-investigator Andy Ingersoll (Caltech) displayed the results at the meeting of the American Geophysical Union in New Orleans.

The microwave data show the temperature structure below the Great Red Spot, revealing that the base is warmer than the top. The warm base probably helps drive the storm’s furious winds. “These winds are three times faster than the jet stream on Earth,” Ingersoll says. “That’s three times hurricane force.”

Although this is the deepest any instrument has ever probed, the Red Spot’s roots are still buried beyond the 200-mile detection range of Juno’s microwave radiometer.

New Radiation Zone

Juno has made some other surprising discoveries during its eight Jupiter flybys (the next one will occur on December 16th).

During its sixth science orbit, Juno passed only 2,200 miles from the equatorial zone’s upper atmosphere, There, the Jupiter Energetic Particle Detector Instrument (JEDI) detected hydrogen, oxygen, and sulfur ions moving at almost the speed of light — markers of a new radiation zone surrounding the planet.

Researchers think this radiation originates in gas around the moons Io and Europa. Energetic neutral atoms from this gas hit Jupiter’s upper atmosphere, which strips away electrons and turns the particles into high-energy ions.

At higher latitudes, Juno’s Stellar Reference Unit (SRU-1) found a different population of heavy ions within Jupiter’s already-known radiation belts. The belts contain mostly electrons streaming around the planet at close to the speed of light. Yet somehow heavy, high-energy ions are finding their way into the belts too.

“We knew we'd see lots of relativistic electrons in the high latitudes but the high energy ions were a surprise," says Heidi Becker (NASA/JPL), who leads Juno’s radiation monitoring investigation.

The find itself is mysterious, as the SRU-1 is a navigation system that’s heavily shielded against radiation. Yet these particles manage to reach the detector inside the unit, where they appear as bright white spots in the detector's output.

Juno has just completed the first quarter of its science mission, which calls for 32 orbits around Jupiter. Juno's principal investigator, Scott Bolton (Southwest Research Institute), says the spacecraft systems appear to be in good shape, but he warns that the second half of the mission will be more technically demanding for the spacecraft.

“The way [the mission] is designed, at the end of the mission it's getting more and more radiation and so the last few orbits are the very worst,” Bolton said. “My guess is that if we're able to do an extended mission, it won't be something that goes for three more years.”