NASA’s Juno mission is scheduled to acquire images of the Jovian moon on Dec. 15 as part of its ongoing exploration of Jupiter’s inner moons. Now in the second year of its extended mission exploring Jupiter’s interior, the solar-powered probe made a close flyby of Ganymede in 2021 and a flyby of Europa earlier this year. “The team is really excited that Juno’s extended mission includes the study of Jupiter’s moons. With each close flyby, we were able to gain a lot of new information,” said Juno principal investigator Scott Bolton of the Southwest Research Institute in San Antonio.
“Juno’s sensors are designed to study Jupiter, but we were excited about how well they could do double duty observing Jupiter’s moons.” Several papers based on the June 7, 2021 Ganymede flyby were recently published in the Journal of Geophysical Research and Geophysical Research Letters. They include insights into the moon’s interior, surface composition and ionosphere, along with its interaction with Jupiter’s magnetosphere, from data collected during the flyby. Preliminary results from Juno’s September 9 flyby of Europa include the first 3D observations of Europa’s icy shell.
Under the ice
During the flybys, Juno’s Microwave Radiometer (MWR) added a third dimension to the mission’s exploration of the Jovian moons: it provided a groundbreaking look beneath the water ice crust of Ganymede and Europa to obtain data on its structure, purity and temperature down to about 15 miles (24 kilometers) below the surface . Visible light images obtained by the spacecraft’s JunoCam probe, as well as previous missions to Jupiter, indicate that Ganymede’s surface is characterized by a mixture of older dark terrain, younger bright terrain, and bright craters, as well as linear features that are potentially associated with tectonic activity.
“When we combined the MWR data with the surface imagery, we found that the differences between these different terrain types are not just profound,” Bolton said. “The young, light terrain appears cooler than the dark, with the city-sized impact crater Tros being the coolest area of the sample. Initial analysis by the science team suggests that Ganymede’s conductive ice shell may have an average thickness of about 30 miles or more, with the possibility that the ice may be significantly thicker in certain areas.
Magnetospheric fireworks
During the probe’s close approach to Ganymede in June 2021, Juno’s Magnetic Field (MAG) and Jovian Auroral Distributions Experiment (JADE) instruments recorded data showing evidence of disruption and reformation of the magnetic field connection between Jupiter and Ganymede. Juno’s Ultraviolet Spectrograph (UVS) observed similar events with the moon’s ultraviolet auroral emissions, arranged in two ovals that wrap around Ganymede.
“Nothing is easy—or small—when you have the largest planet in the solar system as your neighbor,” said Thomas Greathouse, Juno scientist at SwRI. “This was the first measurement of this complicated interaction on Ganymede. This gives us a very early tantalizing taste of the information we expect to hear from JUICE” – ESA’s (European Space Agency) JUpiter ICy moon explorer – “and NASA’s Europa Clipper mission.”
Volcanic future
Jupiter’s moon Io, the most volcanic place in the solar system, will remain the focus of the Juno team for the next year and a half. Their exploration of the moon on Dec. 15 will be the first of nine flybys — two of them from a distance of just 930 miles (1,500 kilometers). Juno scientists will use these flybys to conduct the first high-resolution monitoring campaign on a magma-covered moon, studying Io’s volcanoes and how volcanic eruptions interact with Jupiter’s powerful magnetosphere and auroras.
More about the mission
NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Juno mission for principal investigator Scott J. Bolton of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama for the agency’s Science Mission Directorate in Washington. Lockheed Martin Space in Denver built and operates the spacecraft.
