On Monday, NASA’s Juno spacecraft will come within 645 miles of the surface of Jupiter’s largest moon, Ganymede. “The flyby will be the closest a spacecraft has come to the solar system’s largest natural satellite since NASA’s Galileo spacecraft made its penultimate close approach back on May 20, 2000,” reports Phys.Org. From the report: Along with striking imagery, the solar-powered spacecraft’s flyby will yield insights into the moon’s composition, ionosphere, magnetosphere, and ice shell. Juno’s measurements of the radiation environment near the moon will also benefit future missions to the Jovian system. Ganymede is bigger than the planet Mercury and is the only moon in the solar system with its own magnetosphere — a bubble-shaped region of charged particles surrounding the celestial body.
Juno’s science instruments will begin collecting data about three hours before the spacecraft’s closest approach. Along with the Ultraviolet Spectrograph (UVS) and Jovian Infrared Auroral Mapper (JIRAM) instruments, Juno’s Microwave Radiometer’s (MWR) will peer into Ganymede’s water-ice crust, obtaining data on its composition and temperature. Signals from Juno’s X-band and Ka-band radio wavelengths will be used to perform a radio occultation experiment to probe the moon’s tenuous ionosphere (the outer layer of an atmosphere where gases are excited by solar radiation to form ions, which have an electrical charge).