Bristling with volcanoes like a prickly pig with feathers, Jupiter’s moon Io is the most volcanically active world in the Solar System. At any given time, about 150 of Io’s roughly 400 active volcanoes are erupting. Constantly spews lava and gas; a veritable volcanic excrement factory.
And thanks to Juno’s Jovian Infrared Auroral Mapper (JIRAM), which images Jupiter and its surroundings, we now know a lot more about what a gloriously hot mess Io is.
“The high spatial resolution of JIRAM’s infrared images, combined with Juno’s favorable position during the flyby, revealed that Io’s entire surface is covered with lava lakes contained within caldera-like features,” says astrophysicist Alessandro Mura of National Institute of Astrophysics in Italy.
“In the region of Io’s surface for which we have the most complete data, we think about 3 percent of it is covered by one of these molten lava lakes.”
Yo is the victim of an elaborate game of gravitational tug-of-war. Its orbit around Jupiter is not perfectly circular, meaning that the attraction between the moon and the planet changes in intensity over time. In addition, Jupiter’s other Galilean moons—Callisto, Europa, and Ganymede—have enough mass to exert their own gravitational influence on Io.
The result of all this conflicting gravitational influence is stress on Io’s interior, which generates heat that erupts in the form of volcanism. The little moon is a hot potato.
While we have a pretty good understanding of the dynamics that squeeze and stretch Io’s interior, and the effect it all has on the wider environment around Jupiter and the gas giant itself, there’s a lot we don’t know about how volcanism plays out on the surface of Io.
That, fortunately, fell within Juno’s purview. As the probe explores Jovian space, it makes flybys of some of the moons, using its instruments to gather data more up close and personal than we’ve ever gotten before. The probe recently performed a series of very close flybys of Io, revealing the sulphurous moon in incredible detail.
We’ve seen plumes from actual volcanic eruptions and lakes of lava glistening on the surface. Scientists have now analyzed some of that data, particularly the infrared observations taken by JIRAM, which reveal heat signatures on Io’s surface.
From this, scientists have been able to observe lava lakes that consist of a ring of exposed liquid lava flowing in at the edges, with a solidifying crust in the center of the molten lake and forming high walls of the lake around the bowl-shaped patera in which the lava gathers. This finally reveals the most dominant form of volcanism on Io.
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“We now have an idea of what the most common type of volcanism is on Io: huge lava lakes where magma moves up and down,” says Mura.
“The lava crust is forced to break against the lake walls, forming the typical lava ring seen in Hawaiian lava lakes. The walls are probably hundreds of meters high, which explains why magma is not usually observed pouring out of the patera and moving through on the moon surface.”
This suggests that lava enters the patera from a magma reservoir below the surface and drains in the same way, causing the lakes to rise and fall. The central crust rubs against the walls of the lake as it moves up and down, breaking the edges and as a result a ring of lava forms around the perimeter of the lake.
The other possibility is that the edges of the crust become heavy and sink under the lava, again resulting in a ring.
“The observations reveal fascinating new information about Io’s volcanic processes,” said Juno principal investigator Scott Bolton of the Southwest Research Institute in the US.
“Combining these new results with Juno’s long-term campaign to observe and map the volcanoes at Io’s previously unseen north and south poles, JIRAM is proving to be one of the most valuable tools for learning how this tortured world works.”
The study was published in Nature Communications.
