Volcanoes on Jupiter's Moon Io Are All Wrong

The hundreds of volcanoes on Io are strangely farther east than they're supposed to be.

The hundreds of volcanoes on Jupiter's moon Io aren't where they're supposed to be, scientists say.

Io's major volcanic activity is concentrated 30 to 60 degrees farther east than models of its internal heat profile predict, a recent study reports, suggesting that the exotic, volcanic Jupiter moon Io is even more mysterious than researchers had previously thought.

"The unexpected eastward offset of the volcano locations is a clue that something is missing in our understanding of Io," study lead author Christopher Hamilton, of the University of Maryland, said in a statement. "In a way, that's our most important result. Our understanding of tidal heat production and its relationship to surface volcanism is incomplete."

Io is the most volcanic body in the solar system, boasting activity 25 times that of Earth. Some of Io's volcanoes blast plumes of sulfur and other material 250 miles (400 kilometers) above the moon, which is completely resurfaced every million years or so. On Thursday (April 4), NASA released a video of Io's volcano plumes based on five images snapped by the agency's Pluto-bound New Horizons spacecraft in March 2007. (Amazing Photos of Io by NASA Spacecraft)

This intense activity is ultimately generated by gravitational tugs from Jupiter, with an assist from the nearby moons Europa and Ganymede.

Io completes two orbits for every one that Europa makes, and four for every one of Ganymede's laps. As a result of this regular timing, Europa and Ganymede have pulled the orbit of Io into an oval, with explosive consequences for the 2,260-mile-wide (3,640 km) moon.

As Io moves closer to Jupiter, the planet's powerful gravity pulls hard on the moon, deforming it. This force decreases as Io retreats, and the moon bounces back. This cycle of flexing creates friction in Io's interior, which in turn generates enormous amounts of volcano-driving tidal heat.

Common sense suggests that Io's volcanoes would be located above the spots with the most dramatic internal heating. But Hamilton and his colleagues found that the volcanoes are significantly farther to the east than expected.

They reached this surprising conclusion after studying data gathered by several ground-based telescopes and a number of spacecraft, including NASA's Voyager and Galileo probes, then comparing this information to a detailed geologic map of Io that scientists put together last year.

What's causing the disconnect between expected and observed volcano locations remains a mystery. It's possible that Io is rotating faster that scientists think, researchers said. Or models of Io's tidal heating may be missing some components, such as the complications caused by an underground 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," Hamilton said. "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."

Learning more about how Io's tidal heating works could shed light on the ability of other moons in the solar system to support life, researchers said. Tidal heating is thought to be the force making subsurface oceans of liquid water possible on frigid, ice-covered satellites, such as Europa and Saturn's moon Enceladus.

The study was published in January in the journal Earth and Planetary Science Letters.

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This still from five-frame photo sequence by NASA's New Horizons mission captures the giant plume from the Tvashtar volcano on Jupiter's moon Io. Only the upper part of the plume is visible from this vantage point.

On August 4, the much-anticipated "Wonders of the Solar System" documentary will premier on the Science Channel.

Presenter and physicist Prof. Brian Cox will show you the hidden mysteries of our interplanetary neighborhood, as well as breathtaking sights of the planets, moons and the sun. Cox will also examine some of Earth's extreme environments to see how life has adapted, perhaps helping us understand whether life can exist elsewhere in our solar system. To provide a taster of what you can expect from "Wonders," Discovery News has gathered some facts, figures and the best images of our solar system to assemble a special Wide Angle supporting this groundbreaking documentary. Let's begin, in the orbit of the solar system's biggest planet, Jupiter...

Moons of Jupiter: Io

Welcome to Jupiter, the solar system's biggest planet and host to more than 63 peculiar moons -- a steady contender for moons compared to satellite-strewn Saturn. From sulfur-spewing furnaces to ice-encrusted oceans, these Jovian satellites are anything but normal! Browse through 10 of our favorites here. If you're looking for a fiery, volcanic spectacle, head to Io, the innermost of Jupiter's "big four" moons. Jupiter's gravity pulls at Io so strongly that the land has tides of up to 300 feet (100 meters). This gravitational tug-of-war produces scorching heat and raises more volcanic activity here than anywhere else in the solar system. Io has a sulfurous surface, and its volcanoes spew silicate magma, causing the hellish moon's surface look like a pizza.

Moons of Jupiter: Metis

While it doesn't look like much in this image (the highest-resolution available!), Metis is Jupiter's closest companion -- for now. It's orbiting the gas giant at a distance of just 75,500 miles (128,000 kilometers) and moving faster than Jupiter spins. Metis is so close to Jupiter's surface, in fact, that it will gradually succumb to the planet's gravity and plunge into its churning clouds. This same principle applies to man-made satellites orbiting the Earth; if their orbit is too low, they'll eventually fall.

Moons of Jupiter: Adrastea

Like Metis, Adrastea is on its way down, eventually: Its orbit is just 1,000 kilometers (621 miles) outside of its fellow doomed moon. The two bodies probably provide lots of the material making up Jupiter's main ring, shown in this Galileo spacecraft image. Adrastea is also tiny at a wee 12 miles (20 kilometers) in diameter.

Moons of Jupiter: Ganymede

If Ganymede orbited the sun instead of Jupiter, it would be a planet of its own -- it's even bigger than Mercury. Its interior is made from layers surrounding a rocky core, and its surface is covered in water ice. Although Ganymede doesn't have much of an atmosphere, it does have some ozone gas near its surface. This gas comes from charged particles in Jupiter's magnetic field smacking into the moon's icy crust.

Moons of Jupiter: Themisto

We're not entirely sure what Themisto looks like, but scientists know it one odd little satellite. Unlike most other moons, Themisto is oblong and doesn't fit into the traditional groups of Jovian moons. Because this body is so small -- just 5 miles (8 kilometers) in diameter -- astronomers in 2000 confused it for a new object when it was originally found in 1975. Shown here is a speculative illustration of how the irregular moon might be shaped.

Moons of Jupiter: Callisto

Along with Io, Ganymede, and Europa (which is yet to come in this slide show), Callisto is one of the four Galilean satellites. These are the moons of Jupiter that Galileo discovered while looking through a telescope in 1610. Callisto is about the same size as Mercury, and it's a heavily cratered moon that has almost no geological activity. Callisto's surface may also be one of the oldest landscapes in the solar system, including Earth's moon -- about 4 billion years old.

Moons of Jupiter: Thebe

Along with Metis and Adrastea, Thebe was discovered by scientists studying images from the Voyager spacecraft in 1979 and 1980. It's closer to Jupiter than Io is, but it's not so close that it's in danger of losing its altitude. The material in Jupiter's Gossamer ring probably comes from Thebe and another moon, Amalthea.

Moons of Jupiter: Amalthea

Speaking of Amalthea, shown here is an artist's rendition of the mysterious moon (inset: our best real view so far). Astronomers don't know much about it, but they do know it's the reddest body in the solar system. Unlike the other three moons that lie within Io's orbit -- Thebe, Metis and Adrastea -- Amalthea wasn't discovered by the Voyager science team. Edward Emerson Barnard discovered Amalthea it in 1892, and it had been almost 300 years since anyone had discovered a new moon orbiting Jupiter. Before that, the last person to discover a Jovian moon was Galileo.

Moons of Jupiter: S/2000 J11

This not-to-be-named moon marks an interesting dividing line in the wealth of satellites orbiting Jupiter. S/2000 J11, named after it was found in 2000, moves in the same direction that Jupiter spins -- as do all the moons that are closer to the planet. Almost every distant moon, however, orbits in the opposite (retrograde) direction, as this diagram shows. The only known exception is Carpo, sometimes known as Karpo, which was discovered in 2003.

Moons of Jupiter: Europa

About two-thirds of the Earth is covered in water, but Europa has about twice as much water as our home planet. Europa's might surface is covered in ice, but astronomers are almost convinced there is an ocean of liquid water underneath -- an environment shielded from Jupiter's intense radiation that might be hospitable to life. A cold, salty planet might not seem like a good place to live, but there are species on Earth that thrive in just those conditions.

Slideshow originally posted Feb. 2009.