NASA's Juno spacecraft is gearing up for a close encounter with Ganymede, the solar system's largest moon. Marking the first such flyby in 20 years, this pass will deliver fresh data to refine analyses and pave the way for future Jupiter missions.
On Monday, June 7, Juno will zip just over 1,000 kilometers above Ganymede's surface—the closest approach since NASA's Galileo probe on May 20, 2000. Equipped with JunoCam, the spacecraft will capture high-resolution images for comparison with prior missions, revealing any surface changes.
Traveling at 19 kilometers per second, Juno can snag up to five photos during this brief flyby. Two additional passes are slated for next week.
Scientists will also analyze the moon's crustal composition. "Ganymede's shell features light and dark regions, hinting at pure ice in some areas and 'dirty' ice in others," explains Scott Bolton of the Southwest Research Institute in San Antonio. These insights will clarify the moon's ice renewal processes over time.
The mission will probe Ganymede's ionosphere—the outermost atmospheric layer—using X and Ka band radio signals. "As Juno passes behind Ganymede, signals will traverse its ionosphere, producing detectable frequency shifts captured by Australia's Deep Space Network antennas," notes Dustin Buccino of NASA's Jet Propulsion Laboratory. These measurements could illuminate links between Ganymede's ionosphere, magnetic field, and Jupiter's magnetosphere.
Beyond updating Ganymede studies, these flybys support upcoming Jupiter missions.
The European Space Agency's Jupiter Icy Moons Explorer (JUICE), launched in 2022, will conduct repeated flybys of Callisto, Europa, and Ganymede before orbiting the latter around 2032.
NASA's Europa Clipper, launching in 2024 on a commercial rocket, targets Europa with an arrival in 2029 or 2030.
