NASA’s Juno spacecraft will make the closest flyby of Jupiter’s moon Io, that any spacecraft has made in over 20 years, on Saturday, Dec. 30. Coming within roughly 930 miles (1,500 kilometers) from the surface of the most volcanic world in our solar system, the pass is expected to allow Juno instruments to generate a firehose of data.

“By combining data from this flyby with our previous observations, the Juno science team is studying how Io’s volcanoes vary,” said Juno’s principal investigator, Scott Bolton of the Southwest Research Institute in San Antonio, Texas. “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.”

A second ultra-close flyby of Io is scheduled for Feb. 3, 2024, in which Juno will again come within about 930 miles (1,500 kilometers) of the surface.

The spacecraft has been monitoring Io’s volcanic activity from distances ranging from about 6,830 miles (11,000 kilometers) to over 62,100 miles (100,000 kilometers), and has provided the first views of the moon’s north and south poles. The spacecraft has also performed close flybys of Jupiter’s icy moons Ganymede and Europa.

“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,” said Bolton.

Now in the third year of its extended mission to investigate the origin of Jupiter, the solar-powered spacecraft will also explore the ring system where some of the gas giant’s inner moons reside.

All three cameras aboard Juno will be active during the Io flyby. The Jovian Infrared Auroral Mapper (JIRAM), which takes images in infrared, will be collecting the heat signatures emitted by volcanoes and calderas covering the moon’s surface. The mission’s Stellar Reference Unit (a navigational star camera that has also provided valuable science) will obtain the highest-resolution image of the surface to date. And the JunoCam imager will take visible-light color images.

JunoCam was included on the spacecraft for the public’s engagement and was designed to operate for up to eight flybys of Jupiter. The upcoming flyby of Io will be Juno’s 57th orbit around Jupiter, where the spacecraft and cameras have endured one of the solar system’s most punishing radiation environments.

“The cumulative effects of all that radiation has begun to show on JunoCam over the last few orbits,” said Ed Hirst, project manager of Juno at NASA’s Jet Propulsion Laboratory in Southern California. “Pictures from the last flyby show a reduction in the imager’s dynamic range and the appearance of ‘striping’ noise. Our engineering team has been working on solutions to alleviate the radiation damage and to keep the imager going.”

Click here to learn more about NASA's Juno Mission.