On June 7, NASA's Juno spacecraft reached within 645 miles (1,038 km) of the surface of Jupiter's largest moon, Ganymede, making the flyby the closest a spacecraft has come to the solar system's largest natural satellite since NASA's Galileo spacecraft.
Besides the striking imagery, the solar-powered spacecraft's flyby yielded insights into the moon's composition, ionosphere, magnetosphere, and ice shell and is likely to provide measurements of the radiation environment near the moon to 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. The photographs reveal the surface in incredible detail, with craters, clearly distinguishable dark and bright landscapes, and extensive structural patterns that could be linked to tectonic faults.
"This is the closest any spacecraft has come to this mammoth moon in a generation, we are going to take our time before we draw any scientific conclusions, but until then we can simply marvel at this celestial wonder" said Scott Bolton of the Southwest Research Institute in San Antonio.
The JunoCam visible-light imager on the spacecraft caught nearly a full side of the water-ice-encrusted moon using its green filter. When variations of the same image with the camera's red and blue filters become available, imaging professionals will be able to create a color portrait of Ganymede. The image resolution is approximately 0.6 mile (1 kilometre) per pixel.
Furthermore, Juno's Stellar Reference Unit, a navigational camera that keeps the spacecraft on track, captured a black-and-white image of Ganymede's dark side (the side opposite the Sun) awash in weak light dispersed off Jupiter. The pixel resolution ranges from 0.37 to 0.56 miles (600 to 900 metres).
Heidi Becker, Juno's radiation monitoring lead at JPL says, "The conditions in which we collected the dark side image of Ganymede were ideal for a low-light camera like our Stellar Reference Unit, so this is a different part of the surface than seen by JunoCam in direct sunlight. It will be fun to see what the two teams can piece together."
In the coming days, the spacecraft will send more photographs from its Ganymede flyby.
