NASA’s Juno spacecraft successfully made the second of two close flybys of Io, the most volcanic moon in the solar system, on February 3, giving scientists their best look at this satellite of Jupiter in more than two decades.
The data gathered from these flybys could resolve a mystery about the source of Io’s volcanoes and indicate whether a magma ocean is hiding beneath its surface.
Juno launched in 2011 and arrived at Jupiter in 2016. The spacecraft’s original quest involved exploring the most massive planet in the solar system and its iconic striped atmosphere. But once Juno completed that mandate in 2021, its operators sketched out a new plan for the craft to examine three of Jupiter’s moons, as well as the behemoth’s dainty rings.
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After zipping past the massive Ganymede in 2021 and the icy Europa in 2022, Juno executed its first close flyby of Jupiter’s volcanic moon Io, the innermost of the planet’s four large satellites, on December 30, 2023, followed by its second one on February 3. Each time, the spacecraft flew within about 930 miles (1,500 kilometers) of the surface. Many of the data await scientific analysis and aren’t yet publicly available. But the stunning photographs of this moon’s surface that have been released offer a teaser of the mission’s view of the remarkable world.
“We really saw Io in a new light,” says Scott Bolton, a planetary scientist at the Southwest Research Institute and principal investigator on the Juno mission.
Juno is not the first spacecraft to glimpse Io: both Voyager probes flew by the natural satellite in 1979 and discovered a volcanic nightmare where scientists had expected a quiet gray world like our own moon. And the Galileo,…
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