[LINK] "'Super Earth' May Really Be New Planet Type: Super-Io"

[rfmcdonald]

Jupiter's moon Io, innermost of the four planet-sized Galilean moons, has been famed since the close flyby of the Voyager 1 probe as one of the most exorbitantly volcanic worlds out there, tidal stresses produced by its interactions with Jupiter and the other Galilean moons making this Moon-sized body more volcanically active than Earth, even. Now, it seems like the extraterrestrial planet COROT-7b, a roughly Earth-sized body orbiting a Sun-like star a few hundred light years away, might be the prototype for a new class of planet.

Like Jupiter's moon Io, CoRoT-7b could easily be in the right kind of orbit to experience what's known as tidal heating, according to study co-author Rory Barnes of the University of Washington in Seattle.

On Io, tidal heating is a result of the crust being constantly deformed by the push and pull of Jupiter's gravity. This action generates enough internal heat to drive hundreds of active volcanoes—and the same could be true for CoRoT-7b, Barnes said.

But unlike Io, CoRoT-7b closely orbits a star, not a planet, so tides aren't its only source of heat. Based on previous observations, astronomers know that CoRoT-7b's surface is between 1,832 and 2,732 degrees Fahrenheit (1,000 and 1,500 degrees Celsius).

That's hot enough for there to be "ponds or possibly even oceans of magma," Barnes said. Scientists also know that the planet is tidally locked, which means that only one side ever faces the star.

"There could be volcanism on the back side of the planet," Barnes said. "It could be that on one side the surface is molten, and on the other side there's raging volcanoes."

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In the recent study, presented last month at a meeting of the American Astronomical Society, Barnes and colleagues looked at the possible orbits for CoRoT-7b based on its size and mass, its proximity to its star, and its interactions with a nearby sister planet, CoRoT-7c.

The researchers found that even a slight eccentricity in CoRoT-7b's orbit would generate enough tidal heating to spawn bunches of volcanoes, making the planet much more Io-like than Earthlike.

For starters, just as Io circles close to massive Jupiter, CoRoT-7b orbits very close to its host star, so the influence of gravity is especially strong, Barnes said.

What's more, both Io and CoRoT-7b are tidally locked. In Io's case, this means that one side always faces Jupiter. That side of the moon is being tugged so much harder by gravity that the otherwise round world becomes slightly elongated, with a bulge around the middle.

"Earth does this—we have a tidal bulge due to interactions with the sun and our moon," Barnes noted. "The ocean tides are the result of [gravitational] tides, but rock is also distorted due to tidal effects."

In addition, Io maintains an irregular, elliptical orbit due to interactions with other Jovian moons close by, so its distance to Jupiter changes over time. As Io gets closer to Jupiter, it becomes more elongated, and as it moves away it becomes more spherical.

"If you had a tennis ball and you kept squeezing it, you would get heat from friction," Barnes said. "For Io it's like that, except you're doing it to a planet."