NASA Captures Stunning Images of Jupiter’s Moon Io on Closest Flyby in 20 Years

The Juno spacecraft’s instruments will help scientists better understand volcanic activity on the volatile moon’s surface

red-looking moon with volcanoes appearing as raised dots, the left half in shadow
A view of Jupiter's moon Io captured by NASA's Juno spacecraft on December 30, 2023. NASA / SWRI / MSSS / Jason Perry under CC BY-NC-SA 3.0 DEED

On Saturday, NASA’s Juno spacecraft traveled closer to Jupiter’s moon Io than any spacecraft has in more than 20 years. At its closest, Juno was expected to be around 930 miles from the moon’s surface, NASA said in a statement prior to the flyby.

The spacecraft’s JunoCam instrument, which takes color images in visible light, captured six pictures of Io, the most volcanically active planetary body in our solar system. Juno’s scientific instruments are expected to have gathered a large amount of additional data on the moon during the flyby.

“By combining data from this flyby with our previous observations, the Juno science team is studying how Io’s volcanoes vary,” Scott Bolton, Juno’s principal investigator, says in the statement. “We are looking for how often they erupt, how bright and hot they are, how the shape of the lava flow changes, and how Io’s activity is connected to the flow of charged particles in Jupiter’s magnetosphere.”

NASA’s Juno spacecraft launched from Earth on August 5, 2011, with a mission to study Jupiter. It entered orbit around the gas giant on July 4, 2016. Since then, it has studied the king of planets and its moons, collecting data on Jupiter’s atmosphere and interior. Juno has flown closely by the Jovian moons Ganymede and Europa, and it previously took the first images of Io’s north and south poles.

Beyond the JunoCam, two other cameras aboard the spacecraft imaged Io on the recent flyby: a navigational star camera that can take high-resolution images of the moon’s surface and an infrared camera for detecting heat from volcanoes. Juno is also equipped with a handful of other scientific instruments, including an energetic particle detector, an ultraviolet imaging spectrograph and a microwave radiometer.

The images spotlight the volatile world of Io, which is about one-fourth as wide as Earth. The moon is covered with hundreds of volcanoes, some of which spew lava dozens of miles into the sky. Its surface features lakes of molten lava, and its volcanoes can sometimes be seen from telescopes on Earth. Jupiter’s powerful gravity—as well as that of the large moons Europa, Ganymede and Callisto—contributes to the formation of the volcanoes, per’s Robert Lea.

The recent flyby came during Juno’s 57th orbit around Jupiter. When Juno first reached the gas giant, it took the spacecraft 53 days to complete an orbit. The recent flyby of Io reduced its orbit from 38 days to 35 days.

Juno is expected to once again perform a close flyby of Io from around 930 miles away on February 3. This upcoming flyby and the one from last weekend are the closest approaches to the moon since NASA’s Galileo spacecraft reached 112 miles from Io’s surface in 2001, reports NPR’s Joe Hernandez.

“With our pair of close flybys in December and February, Juno will investigate the source of Io’s massive volcanic activity, whether a magma ocean exists underneath its crust, and the importance of tidal forces from Jupiter, which are relentlessly squeezing this tortured moon,” Bolton says in NASA’s statement.

After the February 3 flyby, the spacecraft will only approach Io every other trip around Jupiter and will progressively travel farther and farther from the volcanic moon.

Juno will start studying the composition of Jupiter’s upper atmosphere in April. Then, in September 2025, the spacecraft’s life will come to an end. In the future, NASA’s Europa Clipper spacecraft, set to launch in October this year, will study Jupiter’s moon Europa and its vast, subsurface ocean.

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