NASA's Juno Mission Makes Closest Flyby Past Io

NASA’s Juno mission has made its closest approach yet to Io, Jupiter’s innermost Galilean moon, passing within 1,500 kilometers (930 miles) of the surface on February 3rd. These were the closest Io passes that Juno will make (though the record still goes to the Galileo mission, which passed 112 miles (181 kilometers) from Io in 2001). We now have some new stunning views of the tormented surface, many of which can be viewed on the JunoCam Gallery.

The latest close pass came just before perijove 58, meaning it's the 58th time the probe has circled the giant planet. It has been just over a month since Juno's last close pass of the moon, on December 30, 2023. NASA has revamped Juno's extended mission plan to schedule seven more flybys of Io, for 18 in all, although the remaining passes will be progressively farther away.

The recent set of flybys probed the moon's interior as well as its surface. "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," says Scott Bolton (Southwest Research Institute) in a recent press release.

As other missions have done before it, Juno spied active volcanoes spewing out material along the moon's limb:

And to think, early mission proposals originally didn't even call for the mission to have a camera! Besides proving handy for publish outreach, the probe's JunoCam has also provided great closeup views of the major Jovian moons during the extended phase of the mission, which began in 2021. Lots of these images are worked though by online volunteers, with amazing results.

Close Flybys

Other recent close passes also revealed volcanic activity, including this JunoCam image from late last year:

Io, which is a little larger than Earth's Moon, is the most geologically active world in the solar system. Its core gets a real workout from Jupiter's enormous gravitational field, whose tidal forces heat the moon's interior. The volcanoes in turn spew energetic charged particles into the powerful Io plasma torus, which connects via magnetic field lines back to Jupiter, creating a complex, interactive system.

JunoCam was actually impacted by radiation exposure during the December 30th perijove pass. Engineers used a method known as 'annealing' to use internal heaters on the camera to warm it up and repair the imager for this month's pass.

Juno's End Phase

The Juno mission has thus far spent over seven years at Jupiter, working as the first solar-powered mission in the outer solar system. For most of its mission, Juno has stayed well out of range of the major moons, for safety reasons. The primary mission was to measure Jupiter’s magnetic field and interior, something Juno could do safely from a distance.

Now, though, a series of close passes have shortened Juno's orbit, bringing it down to 33 days. That puts the probe ever closer to Jupiter and its potentially lethal radiation, but also in scientifically interesting regions.

As of this writing, Juno is funded through September 2025. Ultimately, Juno won't share the same fate as the Galileo mission, which burned up in the Jovian atmosphere... such a final deposal orbit is unnecessary, as Juno is now safely within the interior of Europa and cannot contaminate the icy moon. Instead, Juno will spend its days derelict, until it either burns up in the atmosphere of Jupiter or impacts a small interior moon.

Juno is currently the only mission active at Jupiter, but ESA’s Jupiter Icy Moons (JUICE) mission launched just last year and will arrive at Jupiter in 2031. NASA’s Europa Clipper, set to launch on a Falcon Heavy rocket on October 10th, will beat JUICE to Jupiter, arriving in 2030.

In the meantime, we’ll ride with Juno for one more year of awe-inspiring exploration.