The largest moon in our solar system got its first close-up in more than 20 years on Monday.
NASA’s Juno mission took the images as it swung within 645 miles (1,038 kilometers) of Ganymede’s surface during a flyby, the nearest a spacecraft has been to the moon since the Galileo spacecraft made its approach in May 2000.
“This is the closest any spacecraft has come to this mammoth moon in a generation,” said Juno Principal Investigator Scott Bolton of the Southwest Research Institute in San Antonio, Texas.
“We are going to take our time before we draw any scientific conclusions, but until then we can simply marvel at this celestial wonder.”
At 3,270 miles across (5,262.4 kilometers), this giant moon is larger than the planet Mercury.
The photos – taken by two of three cameras on the spacecraft – show the surface in incredible detail, with craters, distinct dark and bright terrain, and long structural features, which NASA said were possibly linked to tectonic faults.
The spacecraft has been observing Jupiter and its moons since July 2016.
The moon is named for a cupbearer to the ancient Greek gods. In addition to being the largest natural satellite in our solar system, Ganymede is also the only moon to have a magnetic field. This causes auroras to glow around the moon’s north and south poles.
Ganymede has an iron core covered by a layer of rock that is topped off with a thick ice shell. It’s possible that there is a subsurface ocean and astronomers discovered evidence of a thin oxygen atmosphere on the moon in 1996 using the Hubble Space Telescope. This atmosphere is too thin to support life.
Dark side of Ganymede
Using its green filter, the spacecraft’s JunoCam visible-light imager captured almost an entire side of the moon, which is encrusted in water ice, NASA said.
NASA said it hoped to later provide a “color portrait” when it has versions of the same image taken with the camera’s red and blue filters.
In addition, Juno’s Stellar Reference Unit, a navigation camera that keeps the spacecraft on course, snapped a black-and-white image of Ganymede’s dark side (the side opposite the sun).
“The conditions in which we collected the dark side image of Ganymede were ideal for a low-light camera like our Stellar Reference Unit,” said Heidi Becker, Juno’s radiation monitoring lead at the NASA Jet Propulsion Laboratory. “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.”
The spacecraft will send more images from its Ganymede flyby in the coming days. NASA said the raw images would be made available on its website.
The solar-powered spacecraft’s encounter with the moon is expected to shed light on its composition, its magnetic field and icy shell.