Why Is Particular Moon of Jupiter So Volcanically Active?

gravitational tug-of-war between Jupiter and large moons is significant

By Jonny Lupsha, Wondrium Staff Writer

Jupiter is orbited by nearly 80 moons, including four discovered by Galileo. The third largest moon, Io, regularly bursts with explosive volcanic activity. Why does Io have so much volcanic activity?

The third largest moon of Jupiter, Io, is known for its splotchy yellow surface, covered by black spots of volcanic activity. Photo by NASA / Wikimedia Commons / Public Domain

Jupiter may be the largest planet in our solar system, but that’s not its only record-setting feature. One of its moons, Io, is the most volcanically active world in the entire solar system. In fact, while Earth’s volcanoes only emit sulfur compounds up to six miles above Earth’s surface, the sulfur from Io’s volcanoes reaches up to 208 miles above Jupiter’s surface. Io’s volcanoes erupt due to very different reasons than their counterparts on Mercury, Venus, Earth, and Mars.

News recently broke that scientists have detected a different kind of eruption occurring on Io’s surface. While a coronagraphic technique, in use since 2017, is being used to observe this new volcanic activity, we know plenty about Io’s other volcanic activities. In her video series A Field Guide to the Planets, Dr. Sabine Stanley, Bloomberg Distinguished Professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at Johns Hopkins University, sheds light on the mysterious world of Io.

What Makes Io Unique?

Astronomers and planetary scientists have long observed Io’s splotchy yellow surface, which is covered by black spots. Each of those spots is a volcano surrounded by sulfur-rich magma from its eruptions.

“Mercury, Venus, Earth, and Mars also have volcanoes, but what’s different at Io is that its volcanoes are powered by gravitational tidal forces from Jupiter and are still active today,” Dr. Stanley said. “We can actually see them erupt in real-time as witnessed by the New Horizons spacecraft, which zipped by Jupiter in 2007 on its way to Pluto.”

Before New Horizons, the Galileo mission spent several years around Jupiter, repeatedly observing Io’s surface, which changes due to its volcanoes. When the volcanoes erupt and spit matter high into the sky, some of the volcanic material becomes part of Io’s thin atmosphere. Other material escapes the moon, entirely.

“Io loses about one metric ton per second of gases and dust,” Dr. Stanley said. “In a sense, Io is a terrible polluter of the Jovian system, spewing sulfur and other material all over the place. Io is the most volcanically active world in the solar system.”

Why Is Io So Volcanically Active?

Over 400 volcanoes have been mapped on Io. The reason for its high volcanic activity is that Io’s interior is constantly being squeezed and stretched, like a stress ball, by tidal interactions. These tidal forces come from Jupiter and one of its other large moons—Europa—playing a sort of tug-of-war over Io.

“Io orbits Jupiter and is tidally flexed, just like our Moon is squeezed and stretched while orbiting Earth,” Dr. Stanley said. “This gives Io a tidal bulge, making it fatter at the equator than the poles, but there’s a difference between our Moon and Io: Io also feels the gravitational tug of Europa since that moon is so close. The tug-of-war between Jupiter and Europa has given Io’s orbit a small but important ellipticity.”

Io’s elliptical orbit means the distance between Io and Jupiter changes, which in turn constantly changes those tidal forces. One consequence of this is that Io is always changing shape, causing heating from frictional forces. Due to that, Io’s interior is partially molten, all of which adds up to increased volcanic activity.

A Field Guide to the Planets is now available to stream on Wondrium.

Edited by Angela Shoemaker, Wondrium Daily