Universe Today
The Juno spacecraft circling in Jovian space is the planetary science gift that just keeps on giving. Although it's spending a lot of time in the strong (and damaging) Jovian radiation belts, the spacecraft's instruments are hanging in there quite well. In the process, they're peering into Jupiter's cloud tops and looking beneath the surface of the volcanic moon Io.
Members of Juno's science team talked about the craft's discoveries at a meeting in Vienna, Austria, on April 29th. “Everything about Jupiter is extreme," said Juno principal investigator Scott Bolton. "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.”
Artist's concept of the Juno spacecraft at Jupiter. Courtesy NASA.
The recent studies the team reported on were conducted with several instruments, including the Microwave Radiometer (MWR), the Jovian Infrared Auroral Mapper (JIRAM), and the Radio and Plasma Wave Sensor (WAVES). Because Juno is in a variable orbit, scientists can get continued information about all aspects of the planet and its moons. “One of the great things about Juno is its orbit is ever-changing, which means we get a new vantage point each time as we perform a science flyby,” said 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.”
Probing Jovian Clouds
The MWR and JIRAM essentially provide temperature probes of the clouds on Jupiter and the maelstrom of volcanic activity on Io. Early in 2023, Juno's radio instruments began sending radio signals between Earth and Juno through Jupiter's clouds. As the radio signals passed through, the atmospheric layers "bent" the waves. Scientists measure the "bending" and get precise information about the temperatures and densities of the gases in the Jovian atmosphere.
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. Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM
The radio occultation soundings showed that the area of Jupiter's north polar stratospheric cap is a pretty balmy 11 degrees Celsius (about 51 F). The region is surrounded by high-speed winds that clock a decent 161 km/hour (100 mph). In addition, Juno's JunoCam and JIRAM have observed the motion of a giant polar cyclone, along with eight smaller ones that circle around it. These seem to stick to the polar region, although they tend to drift and migrate toward the poles in a cycle. As they move together, these interact and slow down over time. On Earth, most cyclones also drift to the poles, but break up as they lose access to moist air and warm temperatures that normally sustain them. Atmospheric modeling based on the Jovian cyclonic actions could well help explain how similar storms work on Earth and other planets.
“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. “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.”
Digging Into Io
Everybody knows about Io, the most volcanically active world in the solar system. It orbits Jupiter embedded inside the strong Jovian radiation belts, and its volcanoes spew out materials that end up in those belts. So, it makes sense that the Juno team uses everything at its disposal to learn more about that volcanic activity. That includes the MWR and JIRAM instruments, which combine to take infrared imagery and temperature measurements of Io on and beneath the surface.
“The Juno science team loves to combine very different datasets from very different instruments and see what we can learn,” said Shannon Brown, a Juno scientist at NASA’s Jet Propulsion Laboratory in Southern California. “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.”
A massive hotspot — larger than Earth’s Lake Superior — lies just to the right of Io’s south pole in this annotated image taken by the JIRAM infrared imager aboard NASA’s Juno on Dec. 27, 2024, during the spacecraft’s flyby of the Jovian moon. Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM
Io seems to rearrange itself over time through its intense volcanism. The activity fractures the surface and coats it with lava, often described as "turning itself inside out." Planetary scientists need more information about this constant churning. The Juno data shows that about 10 percent of the surface has remnants of slowly cooling lava lying just below the solid surface and that it acts like a car radiator, moving heat from the interior to the surface before it cools down. In addition, the JIRAM data show evidence for the most energetic eruption Io has experienced to date. It occurred in late 2024 and continues to belch lava and ashes out across the surface. Upcoming observations on May 6th should reveal whether or not the eruption is ongoing.
Juno Continues
The Juno mission has been probing the Jovian system since 2016. It was originally planned to end in 2017. However, it's now in an extended mission through September 2025. Eventually, its orbit will degrade under the strong pull of Jupiter's gravity. That will pull the spacecraft in, and eventually it will disappear into the Jovian atmosphere. Data from this mission will help guide future visits to Jupiter by spacecraft such as the Jupiter Icy Moons Explorer (JUICE) and the Europa Clipper, which is scheduled to arrive at its target in 2030.
For More Information
NASA’s Juno Mission Gets Under Jupiter’s and Io’s Surface
Video: Juno measurements of Io's volcanic hotspots and the most energetic eruption ever measured.
