How did Io dislodge the current theory of volcanism?

Jupiter’s moon, Io, is the only solar system body known, besides Earth, which has igneous volcanic activity. New Horizons took measurements of Io’s volcanic activity in 2013, while on its way to Pluto. The results were surprising.

Io’s volcanic activity was unusual in 2013.

Astronomers imaged three monster eruptions on Jupiter’s volcanic moon Io over a two-week span in August 2013, and released the photos Monday (Aug. 4). The frequency of the blasts surprised researchers, who had recorded just 13 giant Io eruptions from 1978 to 2006.

“We typically expect one huge outburst every one or two years, and they’re usually not this bright,” Imke de Pater of the University of California, Berkeley, lead author of one of two new studies describing the blasts, said in a statement. “Here we had three extremely bright outbursts, which suggest that if we looked more frequently we might see many more of them on Io.” [Jupiter Moon’s Volcanic Plume Seen By Spacecraft (Video)]

At 2,300 miles (3,630 kilometers) wide, Io is about the same size as Earth’s moon. In the past, scientists have referred to Io as a “pizza moon” because the volcanoes dotting its surface give it a pockmarked look.

The gravitational influence of Jupiter and several neighboring moons pull hard on Io, heating up its insides and setting the stage for the satellite’s impressive and unusual volcanism. (While some moons in the outer solar system feature frigid “cryovolcanoes,” Io is the only solar system body besides Earth known to feature volcanoes of hot, molten rock.)

Source: Go here to see the 2013 New Horizons pictures of Io’s eruptions, which were considered to have “astonishingly high thermal emissions.”

In 2013, Io’s volcanoes did not fit an expected pattern.

At the time of the New Horizons flyby, in 2013, the location of Io’s volcanos did not match up with scientific predictions.

Io’s volcanoes are in the wrong place.

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.

Source: See the possible variables the need to be considered in Io’s volcanic model, here.

As a test of its equipment, in the Fall of 2008, New Horizons pointed its Long Range Reconnaissance Imager, LORRI, towards Neptune’s moon, Triton, in an annual test during the 9-year voyage. To see why Triton was the selected target, visit the next page.