A flurry of new discoveries from NASA’s Juno mission Jupiter have taken us beneath the surface of the gas giant’s volcanic moon, Io, and into the world of cyclones playing bumper cars at the north Jovian pole.
Juno arrived at the Jupiter system in 2016, but a failed thruster meant that it is now stuck in a wide, polar orbit that brings it close to Jupiter and its moons every 53 days. Still, during those flybys, Juno has amassed a bevy of high-quality data about Jupiter’s atmosphere, including at the planet’s poles, which had not previously been studied in detail.
At Jupiter’s north pole is a cap of stratospheric haze, which Juno has measured to be cooler than its surroundings by 52 degrees Fahrenheit (11 degrees Celsius). Around the polar cap are jet streams blowing faster than 100 miles per hour (161 kilometers per hour). Below the haze, the north polar region is inhabited by one giant, central cyclone about 1,864 miles (3,000 kilometers) across, surrounded by its “groupies” — eight smaller cyclones between 1,490 and 1,790 miles (2,400 and 2,800 kilometers) in size, far surpassing any similar phenomena we have on Earth.
Juno has been tracking the motion of this system of cyclones in visible and infrared light (in the guise of heat coming from deeper within the atmosphere) since 2016, using its JunoCam and Jovian Infrared Aurora Mapper (JIRAM), respectively. These two instruments have shown that each of the eight cyclones drift towards the pole via a process called “beta drift.” The same process occurs to cyclones on Earth, and is the result of the Coriolis force interacting with the whirling wind pattern belonging to each cyclone. However, on Earth, cyclones never get anywhere near the poles. That’s because the closer they get to cold, dry poles, the more they run out of the warm, moist air that gives them energy. On Jupiter, the atmospheric dynamics are different, and this is not a problem. But once at the pole, Jupiter’s cyclones start bumping into each other.
“These competing forces result in the cyclones ‘bouncing’ off one another in a manner reminiscent of springs in a mechanical system,” said Yohai Kaspi, a Juno co-investigator from the Weizmann Institute of Science in Israel, in a statement. “This interaction not only stabilizes the entire configuration, but also causes the cyclones to oscillate around their central positions, as they slowly drift westward, clockwise, around the pole.”
Meanwhile, away from Jupiter’s atmosphere, Juno has recently been making recurring fly-bys of the innermost Jovian moon, Io — the most volcanic body in the solar system.
During Juno’s flyby of Io on Dec. 27, 2024, the spacecraft spotted what has turned out to be the most energetic volcanic eruption ever recorded on Io. When Juno returned on March 2, the volcano was still spewing lava, and it is expected to still be active during Juno’s next flyby, which takes place on May 6 at a distance of 55,300 miles (89,000 kilometers) from the surface of Io.
But it’s what lies below the surface of Io that has got Juno’s science team excited. By combining the spacecraft’s Microwave Radiometer (MWR) with JIRAM, scientists were able to measure the underground temperature on Io, revealing the presence of subterranean magma flows.
“The Juno science team loves to combine very different datasets from very different instruments and see what we can learn,” said Shannon Brown of NASA’s Jet Propulsion Laboratory. “When we incorporated the MWR data with JIRAM’s infrared imagery, we were surprised by what we saw: evidence of still-warm magma that hasn’t yet solidified below Io’s cooling crust. At every latitude and longitude, there were cooling lava flows.”
Juno has previously ruled out the existence of a large magma ocean beneath Io’s surface that could feed the volcanoes, but these cooling, rising flows could explain how Io’s volcanoes erupt. The science team calculates that about 10% of the moon’s subsurface has these cooling flows, which tells us more about how heat is transported from Io’s hot interior to its surface, allowing the world to frequently resurface itself through lava flows spilling out above ground.
“Io’s volcanoes, lava fields and subterranean lava flows act like a car radiator, efficiently moving heat from the interior to the surface, cooling itself down in the vacuum of space,” said Brown.
The latest Juno results were presented on April 29 at the European Geosciences Union General Assembly in Vienna.
