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Io’s Volcanoes are in the Wrong Place

This five-frame sequence of images from NASA's New Horizons mission captures the giant plume from Io's Tvashtar volcano in March, 2007. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

This five-frame sequence of images from NASA’s New Horizons mission captures the giant plume from Io’s Tvashtar volcano in March, 2007. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

Jupiter’s moon Io features at least 400 active volcanoes, making it the most volcanically active world in our Solar System. However, the location of the volcanoes on Io just doesn’t match up with scientific models that predict how the moon’s interior is heated.

“Rigorous statistical analysis of the distribution of volcanoes in the new global geologic map of Io,” said Christopher Hamilton of the University of Maryland, College Park and the Goddard Spaceflight Center. “We found a systematic eastward offset between observed and predicted volcano locations that can’t be reconciled with any existing solid body tidal heating models.”

Io’s internal heat is created by the tidal forces inflicted from the giant planet Jupiter on one side and from two neighboring moons that orbit further from Jupiter – Europa and Ganymede on the other.

Researchers say there are questions about how this tidal heating affects the moon’s interior. Some propose it heats up the deep interior, but the prevailing view is that most of the heating occurs within a relatively shallow layer under the crust, called the asthenosphere. The asthenosphere is where rock behaves like putty, slowly deforming under heat and pressure.

“Our analysis supports the prevailing view that most of the heat is generated in the asthenosphere, but we found that volcanic activity is located 30 to 60 degrees East from where we expect it to be,” said Hamilton.

On Earth, a simple explanation how volcanoes are created is that when tectonic plates shift in such a way, the subsurface magma is able to flow onto the surface. On Io, the tidal forces from Jupiter actually force Io’s surface to bulge up and down by as much as 100 m, causing magma to flow continuously.

The scientists explained the tug-of-war between Jupiter’s massive gravity and the smaller but precisely timed pulls from two neighboring moons like this:

Io orbits faster than these other moons, completing two orbits every time Europa finishes one, and four orbits for each one Ganymede makes. This regular timing means that Io feels the strongest gravitational pull from its neighboring moons in the same orbital location, which distorts Io’s orbit into an oval shape. This in turn causes Io to flex as it moves around Jupiter.

For example, as Io gets closer to Jupiter, the giant planet’s powerful gravity deforms the moon toward it and then, as Io moves farther away, the gravitational pull decreases and the moon relaxes. The flexing from gravity causes tidal heating — in the same way that you can heat up a spot on a wire coat hanger by repeatedly bending it, the flexing creates friction in Io’s interior, which generates the tremendous heat that powers the moon’s extreme volcanism.

This is a map of the predicted heat flow at the surface of Io from different tidal heating models. Red areas are where more heat is expected at the surface while blue areas are where less heat is expected. Figure A shows the expected distribution of heat on Io's surface if tidal heating occurred primarily within the deep mantle, and figure B is the surface heat flow pattern expected if heating occurs primarily within the asthenosphere. In the deep mantle scenario, surface heat flow concentrates primarily at the poles, whereas in the asthenospheric heating scenario, surface heat flow concentrates near the equator. Credit: NASA/Christopher Hamilton.

This is a map of the predicted heat flow at the surface of Io from different tidal heating models. Red areas are where more heat is expected at the surface while blue areas are where less heat is expected. Figure A shows the expected distribution of heat on Io’s surface if tidal heating occurred primarily within the deep mantle, and figure B is the surface heat flow pattern expected if heating occurs primarily within the asthenosphere. In the deep mantle scenario, surface heat flow concentrates primarily at the poles, whereas in the asthenospheric heating scenario, surface heat flow concentrates near the equator. Credit: NASA/Christopher Hamilton.

But a new geologic map of Io showed the offset of the volcanoes from where the model predicted them to be.

Possibilities to explain the offset include a faster than expected rotation for Io, an interior structure that permits magma to travel significant distances from where the most heating occurs to the points where it is able erupt on the surface, or a missing component in existing tidal heating models, like fluid tides from an underground magma ocean, according to the team.

The magnetometer instrument on NASA’s Galileo mission detected a magnetic field around Io, suggesting the presence of a global subsurface magma ocean. As Io orbits Jupiter, it moves inside the planet’s vast magnetic field. Researchers think this could induce a magnetic field in Io if it had a global ocean of electrically conducting magma.

“Our analysis supports a global subsurface magma ocean scenario as one possible explanation for the offset between predicted and observed volcano locations on Io,” says Hamilton. “However, Io’s magma ocean would not be like the oceans on Earth. Instead of being a completely fluid layer, Io’s magma ocean would probably be more like a sponge with at least 20 percent silicate melt within a matrix of slowly deformable rock.”

Tidal heating is also thought to be responsible for oceans of liquid water likely to exist beneath the icy crusts of Europa and Saturn’s moon Enceladus. Since liquid water is a necessary ingredient for life, some researchers propose that life might exist in these subsurface seas if a useable energy source and a supply of raw materials are present as well. These worlds are far too cold to support liquid water on their surfaces, so a better understanding of how tidal heating works may reveal how it could sustain life in otherwise inhospitable places throughout the Universe.

“The unexpected eastward offset of the volcano locations is a clue that something is missing in our understanding of Io,” says Hamilton. “In a way, that’s our most important result. Our understanding of tidal heat production and its relationship to surface volcanism is incomplete. The interpretation for why we have the offset and other statistical patterns we observed is open, but I think we’ve enabled a lot of new questions, which is good.”

Io’s volcanism is so extensive that it gets completely resurfaced about once every million years or so, actually quite fast compared to the 4.5-billion-year age of the solar system. So in order to know more about Io’s past, we have to understand its interior structure better, because its surface is too young to record its full history, according to Hamilton.

Source: JPL

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • Me April 5, 2013, 2:18 AM

    lol@not supposed to be where they’re at. By who’s claim? Man or nature? Io is so tiny. 400 volcano’s? On this tiny moon? Whoa! That is so incredible. I know about plate tectonics, but the action(s) of Io being squeezed the way it is, is so amazing. The more I thought about it. I figured over 100’s of millions of years, it would of crumbled away by those actions as well as Jupiter’s gravity. Take care all.

    • Danny April 5, 2013, 9:51 AM

      You’re right it is a pretty hardy little moon to withstand all that flexing!

  • Zoutsteen from Holland April 5, 2013, 2:18 AM

    no doubt with vulcanic activity, mass is redistributed causing a snail’s pace balancing rotation to stay Jupiter faced according to mass.

    Kinda like the Earths rotation cause the moon’s Eb and Flow to be out of sinc with the moon. But with IO, its reversed, the vulcano’s plume preference to go one way is probably enough.

  • Skipdallas April 5, 2013, 11:19 AM

    Obviously the models are defective, and need to be re-thought.

  • KhanneaSuntzu April 5, 2013, 12:08 PM

    An adjustment for the model is that the areas with the most outgassing have been so thoroughly “paved over” by repeated volcanism they effectively “scabbed up” the equatorial surface, and the lava gets squeezed out elsewhere. Maybe Io is effectively “cystified”.

  • Torbjörn Larsson April 5, 2013, 2:07 PM

    It is nice to have such an extreme testbed in the system. The tidal habitable zone of gas giants may be where the largest biomass is at in the universe. Certainly Europa has us beaten for ocean mass if the current estimates are correct.

    So it is an important puzzle.

    *******************

    [OP]

    Old Sun System had a giant,

    Io-Io-Oh!

    And around his giant he had a moon,

    Io-Io- … D’oh!

    With a volcano here,

    and a volcano there,

    Here a jet, there a jet,

    Everywhere a jet set.

    Old Sun System had a giant,

    Io-Io-Oh!

    • Me April 5, 2013, 3:52 PM

      Pinch me! I don’t believe it!!! He has a sense of humor! Well done Tor,…well done! Humor is always needed. Makes any job fun as well as eases the tension at anyone job..
      Europa they say has a deep ice surface. Not sure.the depth, but its very thick. They want to take a probe, land it, melt the ice w/a diameter of -‘?’- to get to the liquid H2O. w/a sub-vehicle attached to cruise in the depths. Microbes? Possible. Fish swimming around? That is a huge step, but still possibe. To me it is very probable like for microbes. Take care Tor.

  • zetetic elench April 5, 2013, 3:11 PM

    interesting about the inductive heating of conductive magma. another way to keep things warm in ice moons around gas giants.

  • Aqua4U April 5, 2013, 8:14 PM

    Gravity flexing for sure, but what about Jupiter’s huge magnetic field? Io orbits Jupiter at an average of 17.334 km/s as it moves in and through that huge lopsided field – compressed on Sol’s side and extending to Saturn’s orbit on the other – the strength and direction must change rapidly as Io passes through? That would make Io the solar systems largest electric blender? A HOT electric blender!

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