NASA mission takes first close-up images of Ganymede in two decades

NASA’s Juno probe dove low over Jupiter’s largest moon Ganymede on 7 June, providing the first up-close views of its icy surface in more than two decades.

At its closest, Juno will fly roughly 1000 kilometres above the frozen moon. Ganymede, which at 5260 kilometres wide is larger than the planet Mercury, was previously explored in detail by NASA’s Galileo spacecraft around the turn of the millennium and the Voyager missions in the late 1970s.

This latest visit will also see the probe gather a trove of valuable scientific data, including measurements of the moon’s magnetic field and its mottled crust, which is made of water ice.

“We are very excited about this fly-by,” says Candice Hansen at the Planetary Science Institute in Tucson, Arizona, who leads the team working with the spacecraft’s JunoCam camera.

JunoCam should be able to snap pictures of Ganymede with a resolution of about 1 to 2 kilometres. That level of detail may give researchers a chance to see whether any areas on the moon have been altered – by events such as asteroid impacts – since our last clear view.

“Both Galileo and Voyager imaged Ganymede, and it just turns out that the portion of the surface we will be imaging was best mapped by Voyager, which of course gives us an even longer time base for changes,” says Hansen.

The Juno spacecraft itself is just a month or so away from the end of its primary mission, but earlier this year NASA extended the probe’s time surveying the giant of our solar system. It will go on studying Jupiter and its storm-flecked atmosphere until 2025 and will make further visits to some of the planet’s largest moons, with close swings past Europa next year and Io in 2023.

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