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NASA: Io’s volcanoes are in the wrong place

Io’s volcanoes are in the wrong place, according to NASA and European Space Agency researchers. Jupiter’s moon Io has hundreds of volcanoes, making it the most volcanically active world in the Solar System. However, models that predict how Io’s interior is heated make the case that the location of these volcanoes is wrong.

Io orbits faster than two neighboring moons, Europa and Ganymede. In fact, Io completes two orbits every time Europa finishes one, and four orbits every time Ganymede completes one. This means that Io experiences the strongest gravitational pull from its neighboring moons in the same location, which alters Io’s orbit into an oval shape and causes the moon to flex as it circles Jupiter.

According to a news release from NASA’s Goddard Space Flight Center, the flexing creates friction in Io’s interior, which produces extreme heat that drives the moon’s volcanism. Scientists are still unsure exactly how this tidal heating impacts the moon’s interior. Some theorize that it heats up the deep interior, but the most widely accepted view is that most of the heating takes places within a shallow layer under the crust, known as the asthenosphere.

According to lead author Christopher Hamilton of the University of Maryland, the researchers found evidence to support the theory that most of the heat is produced in the asthenosphere. However, he and his colleagues discovered that volcanic activity is located 30 to 60 degrees East from where they expected it to be.

Hamilton and his colleagues conducted a spatial analysis utilizing a new geologic map of Io. The map offers the most inclusive inventory of Io’s volcanoes to date, allowing patterns of volcanism to be studied in exceptional detail.  Operating under the assumption that volcanoes are typically found above where the most internal heating takes place, the researchers tried out a number of interior models by comparing observed places of volcanic activity to predicted tidal heating patterns.

Hamilton and his colleagues discovered a “systematic eastward offset between observed and predicted volcano locations.” He added that these locations “can’t be reconciled with any existing solid body tidal heating models.”

According to the researchers, there could be numerous explanations for this finding, including a quicker than expected rotation for Io, a mysterious interior structure that allows magma to move major distances from where the most heating takes place to the locations where it can erupt, or something missing in existing tidal heating modals.

According to the news release, the magnetometer instrument on NASA’s Galileo mission identified a magnetic field around Io, suggesting the existence of a global subsurface magma ocean.

“Our analysis supports a global subsurface magma ocean scenario as one possible explanation for the offset between predicted and observed volcano locations on Io,” said Hamilton. He noted, however, that Io’s magma ocean would be more “like a sponge with at least 20 percent silicate melt within a matrix of slowly deformable rock.”

Io gets completely resurfaced approximately once every million years of so because of the moon’s intense volcanism. Hamilton noted that scientists have to learn more about Io’s interior to learn more about its past, because its surface is too young.

The study’s findings are described in detail in the journal Earth and Planetary Science Letters.

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