New Juno images of Io’s fiery volcanoes

JIRAM image of volcanic hotspots - bright red-orange dots - on Io.
Meet Io, Jupiter’s innermost large moon. The red dots – nicknamed the “fires of Io” – are active volcanoes. December 2018 image via NASA’s Juno spacecraft (NASA/JPL-Caltech/SwRI/INAF). Read more about this image.

Jupiter’s moon Io is the most volcanically active world in the solar system – even more active than Earth – with hundreds of volcanoes erupting at any almost given time. The Voyager spacecraft discovered that Io has active volcanoes, back in the late 1970s, and – in the late 1990s and early 2000s – the Galileo mission provided more stunning images of the “fires of Io.” Now, NASA’s current mission at Jupiter – the Juno orbiter spacecraft – has sent back new photos of a volcanic plume on this molten little world (image below). The news was announced by the Southwest Research Institute on December 31, 2018.

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The new images and other data were taken on the winter solstice in Earth’s Northern Hemisphere – December 21 – by various instruments such as the JunoCam camera. The Stellar Reference Unit (SRU), the Jovian Infrared Auroral Mapper (JIRAM) and the Ultraviolet Imaging Spectrograph (UVS) also observed Io for over an hour, to study the moon’s polar regions as well as look for evidence of any current active eruptions.

Juno isn’t designed to study the moons of Jupiter up close, as Galileo or Voyager did. Rather, Juno’s focus is on Jupiter itself. But Juno can and now has still made important observations from a distance. The observations of Io paid off, according to Scott Bolton, principal investigator of the Juno mission and an associate vice president of Southwest Research Institute’s Space Science and Engineering Division:

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

Io half-lit with small white dot on the dark side.
JunoCam image showing a volcanic plume illuminated beyond the terminator of Io, taken on December 21, 2018. Image via NASA/SwRI/MSSS.
Fuzzy image of volcanic eruptions on Io.
Stellar Reference Unit (SRU) image of Io taken on December 21, 2018. Io is softly illuminated by moonlight from another of Jupiter’s moons, Europa. The brightest feature on Io is suspected to be a penetrating radiation signature from an erupting volcano, and several of Io’s other volcanos can also be seen, including a plume circled in the image. Image via NASA/JPL-Caltech/SwRI.

The images were taken during the 17th flyby of Jupiter by Juno. Juno orbits Jupiter, although it never comes very close to any of the moons. The first images were obtained on December 21 at 12:00, 12:15 and 12:20 coordinated universal time (UTC; translate to your time zone), before Io entered Jupiter’s shadow. Io itself is seen as half-illuminated, with an eruption visible as a bright spot just past the edge of the terminator. As explained by Candice Hansen-Koharcheck, the JunoCam lead from the Planetary Science Institute:

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.

Io’s eruptions are so powerful they can be seen even from a long distance away from the moon. In this case, reflected light from the moon Europa also helped to make the plume more visible, as seen in images from the SRU, according to Heidi Becker, lead of Juno’s Radiation Monitoring Investigation, at the Jet Propulsion Laboratory.

As a low-light camera designed to track the stars, the SRU can only observe Io under very dimly lit conditions. Dec. 21 gave us a unique opportunity to observe Io’s volcanic activity with the SRU using only Europa’s moonlight as our lightbulb.

A blue geyser-like volcanic eruption at the edge of Io.
A volcanic eruption on Io seen by the Galileo spacecraft in 1997. Image via NASA/JPL/DLR.
Io's colorful and mottled surface, very many dots, circles, and blotches
Another view from Galileo – Io’s surface is very colorful and mottled, due to ongoing volcanic deposits. Image via NASA/JPL.

Juno’s JIRAM instrument is even more versatile, able to see volcanic hotspots on Io in both daylight and at night. According to Alberto Adriani, a researcher at Italy’s National Institute for Astrophysics:

Though Jupiter’s moons are not JIRAM’s primary objectives, every time we pass close enough to one of them, we take advantage of the opportunity for an observation. The instrument is sensitive to infrared wavelengths, which are perfect to study the volcanism of Io. This is one of the best images of Io that JIRAM has been able to collect so far.

While the new Juno images were taken a lot farther away from Io the the previous ones, there is still a lot of information that scientists can obtain from them. For instance, they can provide new insights into how Jupiter interacts with its five moons – causing phenomena such as Io’s volcanic activity or the freezing of the moon’s atmosphere during an eclipse. Even though Io is very small, its gravitational interaction with Jupiter drives the moon’s volcanoes, which produce huge umbrella-like plumes of sulfur dioxide gas and extensive lava fields. That “stretching” causes friction and intense heat in Io’s interior, sparking massive eruptions across its surface.

Smooth volcanic plains with some wide volcanoes
A closer view of volcanic plains near Io’s south pole, taken by Voyager 1 in 1979. Image via NASA/JPL/USGS.

Io’s volcanoes were first seen by NASA’s Voyager spacecraft in 1979, with the plumes arcing over the mottled and very colorful surface which made the moon look like a giant pizza. The eruptions continuously coat the surface with silicates and sulfur compounds. Io also has an extremely thin atmosphere consisting mostly of sulfur dioxide.

Juno – which orbits Jupiter every 53 days – is approximately halfway through its primary mission, and is scheduled to complete its mapping of Jupiter in July 2021.

Bottom line: Io’s volcanic eruptions are an incredible sight, surprising for a small moon so far from the sun. The earlier Voyager and Galileo missions imaged them in beautiful detail, and now the Juno spacecraft – even though much farther away from Io – has also seen them, providing new observations and data about this geological wonder orbiting Jupiter.

Via SwRI

January 6, 2019

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