NASA’s Juno mission has gathered new findings after peering below Jupiter’s cloud-covered atmosphere and the surface of its fiery moon, Io.
Not only has the data helped develop a new model to better understand the fast-moving jet stream that encircles Jupiter’s cyclone-festooned north pole, it’s also revealed for the first time the subsurface temperature profile of Io, providing insights into the moon’s inner structure and volcanic activity.
Team members presented the findings during a recent news briefing in Vienna at the European Geosciences Union General Assembly.
“Everything about Jupiter is extreme,” says Scott Bolton, principal investigator of Juno at the Southwest Research Institute. “The planet is home to gigantic polar cyclones bigger than Australia, fierce jet streams, the most volcanic body in our solar system, the most powerful aurora, and the harshest radiation belts. As Juno’s orbit takes us to new regions of Jupiter’s complex system, we’re getting a closer look at the immensity of energy this gas giant wields.”
Made with data from the JIRAM instrument aboard NASA’s Juno, this animation shows the south polar region of Jupiter’s moon Io during a 27 December 2024 flyby. The bright spots are locations with higher temperatures caused by volcanic activity; the gray areas resulted when Io left the field of view.
NASA/JPL/SwRI/ASI – JIRAM Team (A.M.)
Lunar radiator
While Juno’s microwave radiometer (MWR) was designed to peer beneath Jupiter’s cloud tops, the team has also trained the instrument on Io, combining its data with Jovian Infrared Auroral Mapper (JIRAM) data for deeper insights.
“The Juno science team loves to combine very different datasets from very different instruments and see what we can learn,” says Shannon Brown, a Juno scientist at 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 cooled crust. At every latitude and longitude, there were cooling lava flows.”
The data suggests that about 10% of the moon’s surface has these remnants of slowly cooling lava just below the surface. The result may help provide insight into how the moon renews its surface so quickly, as well as how heat moves from its deep interior to the surface.
“Io’s volcanos, 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,” says Brown.
Looking at JIRAM data alone, the team also determined that the most energetic eruption in Io’s history (first identified by the infrared imager during Juno’s 27 December 2024 Io flyby) was still spewing lava and ash as recently as 2 March. Juno mission scientists believe it remains active today and expect more observations when the solar-powered spacecraft flies by the fiery moon at a distance of about 89 000 kilometers.
This composite image, derived from data collected in 2017 by the JIRAM instrument aboard NASA’s Juno, shows the central cyclone at Jupiter’s north pole and the eight cyclones that encircle it. Data from the mission indicates these storms are enduring features.
NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM
Colder climes
On its 53rd orbit (18 February 2023), Juno began radio occultation experiments to explore the gas giant’s atmospheric temperature structure. With this technique, a radio signal is transmitted from Earth to Juno and back, passing through Jupiter’s atmosphere on both legs of the journey.
As the planet’s atmospheric layers bend the radio waves, scientists can precisely measure the effects of this refraction to derive detailed information about the temperature and density of the atmosphere.
So far, Juno has completed 26 radio occultation soundings. Among the most compelling discoveries: the first-ever temperature measurement of Jupiter’s north polar stratospheric cap reveals the region is about 11 degrees Celsius cooler than its surroundings and is encircled by winds exceeding 161 kph.
Polar cyclones
The team’s recent findings also focus on the cyclones that haunt Jupiter’s north. Years of data from the JunoCam visible light imager and JIRAM have allowed Juno scientists to observe the long-term movement of Jupiter’s massive northern polar cyclone and the eight cyclones that encircle it. Unlike hurricanes on Earth, which typically occur in isolation and at lower latitudes, Jupiter’s are confined to the polar region.
By tracking the cyclones’ movements across multiple orbits, the scientists observed that each storm gradually drifts toward the pole due to a process called “beta drift” (the interaction between the Coriolis force and the cyclone’s circular wind pattern).
This is similar to how hurricanes on our planet migrate, but Earthly cyclones break up before reaching the pole due to the lack of warm, moist air needed to fuel them, as well as the weakening of the Coriolis force near the poles. What’s more, Jupiter’s cyclones cluster together while approaching the pole, and their motion slows as they begin interacting with neighboring cyclones.
“These competing forces result in the cyclones ‘bouncing’ off one another in a manner reminiscent of springs in a mechanical system,” says Yohai Kaspi, a Juno co-investigator from the Weizmann Institute of Science in Israel. “This interaction not only stabilises the entire configuration, but also causes the cyclones to oscillate around their central positions, as they slowly drift westward, clockwise, around the pole.”
The new atmospheric model helps explain the motion of cyclones not only on Jupiter, but potentially on other planets, including Earth.
“One of the great things about Juno is its orbit is ever-changing, which means we get a new vantage point each time we perform a science flyby,” says Bolton. “In the extended mission, that means we’re continuing to go where no spacecraft has gone before, including spending more time in the strongest planetary radiation belts in the solar system. It’s a little scary, but we’ve built Juno like a tank and are learning more about this intense environment each time we go through it.”
Featured picture: JunoCam, the visible light imager aboard NASA’s Juno, captured this enhanced-color view of Jupiter’s northern high latitudes from an altitude of about 58 000 kilometers above the giant planet’s cloud tops during the spacecraft’s 69th flyby on 28 January 2025.
Image data: NASA/JPL-Caltech/SwRI/MSSS Image processing: Jackie Branc (CC BY)