NASA’s Juno spacecraft is on a mission to study Jupiter, but that’s not the only celestial object in range of its instruments. Jupiter has plenty of moons, and Juno can take a peek at those while it loops around the gas giant. On its most recent orbit of Jupiter, Juno spied something interesting on the moon Io: volcanic activity.
Juno launched in 2011 on a mission to study Jupiter’s atmosphere and internal structure, which it began upon reaching the gas giant in 2016. Juno is currently on a 53-day orbit of Jupiter. NASA initially intended to shorten that orbit considerably, but problems with the spacecraft’s engines made that too risky. One upshot of the longer orbit is that NASA gets more opportunity to observe other elements of the Jovian system like Io.
Scientists have known that Io is geologically active since 1979 when Voyager 1 passed by on its way out of the solar system. Io is slightly larger than Earth’s moon, but its internal heating is driven by tidal forces from Jupiter’s massive gravity. Over the years, it has become apparent just how active Io is — with more than 400 volcanos, Io is considered the most geologically active object in the solar system. So, it’s not unthinkable Juno would spy an eruption if it went looking.
During its 16th orbit of Jupiter (the halfway point of the mission), scientists turned Juno’s instruments to Io just as it began passing into the shadow of Jupiter. Four of Juno’s cameras spotted a bright flash across the terminator on the dark side of Io (see above) indicating a volcanic eruption.
Juno first spotted the eruption at 12:00 UTC on December 21st. The ground is already in shadow, but the bright spot indicates the volcanic cloud is tall enough to reflect sunlight. The above image came from the JunoCam in the visible range, reconstructed from red, blue, and green images. Below, you can see the eruption via the Jovian Infrared Auroral Mapper (JIRAM). The bright spot of the eruption indicates exceptionally high temperatures. While not the intended use case for JIRAM, the team was pleasantly surprised at how well it worked for observing the plume on Io.
NASA expects to wrap up Juno’s primary science mission in July 2021 when the probe will complete its map of Jupiter. Juno has already helped scientists understand Jupiter’s atmosphere and magnetic field. The second half of the mission could shed light on the planet’s zonal winds and internal structure.
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