Juno Observes Volcanic Plume on Io

NASA’s Juno orbiter has captured images of a volcanic plume on Jupiter’s moon Io during the mission’s 17th flyby of the giant planet.

JunoCam acquired three images of Io prior to when it entered eclipse, all showing a volcanic plume illuminated beyond the terminator; the image shown here, reconstructed from red, blue and green filter images, was acquired at 12:20 p.m. GMT on December 21, 2018; Juno was 186,411 miles (300,000 km) from Io. Image credit: NASA / SwRI / MSSS.

Four instruments onboard Juno — a camera called JunoCam, the Stellar Reference Unit, the Jovian Infrared Auroral Mapper and the Ultraviolet Imaging Spectrograph — observed Io for over an hour, providing a glimpse of the moon’s polar regions as well as evidence of an active eruption.

JunoCam acquired the new images of Io on December 21, 2018, at 12:00, 12:15 and 12:20 p.m. GMT before Io entered Jupiter’s shadow.

The images show the moon half-illuminated with a bright spot seen just beyond the terminator, the day-night boundary.

“The ground is already in shadow, but the height of the plume allows it to reflect sunlight, much like the way mountaintops or clouds on the Earth continue to be lit after the Sun has set,” said Dr. Candice Hansen-Koharcheck, JunoCam lead from the Planetary Science Institute.

At 12:40 p.m. GMT, after Io had passed into the darkness of total eclipse behind Jupiter, sunlight reflecting off nearby moon Europa helped to illuminate Io and its plume.

The brightest feature on Io in the images is thought to be a penetrating radiation signature, a reminder of this moon’s role in feeding Jupiter’s radiation belts, while other features show the glow of activity from several volcanoes.

“We knew we were breaking new ground with a multi-spectral campaign to view Io’s polar region, but no one expected we would get so lucky as to see an active volcanic plume shooting material off the moon’s surface,” said Juno mission principal investigator Dr. Scott Bolton, from the Southwest Research Institute’s Space Science and Engineering Division.

“This is quite a New Year’s present showing us that Juno has the ability to clearly see plumes.”

“The December 21 flyby gave us a unique opportunity to observe Io’s volcanic activity with Juno’s Stellar Reference Unit using only Europa’s moonlight as our lightbulb,” said Dr. Heidi Becker, lead of Juno’s Radiation Monitoring Investigation at NASA’s Jet Propulsion Laboratory.

“The latest images can lead to new insights into the gas giant’s interactions with its five moons, causing phenomena such as Io’s volcanic activity or freezing of the moon’s atmosphere during eclipse,” Dr. Bolton said.