Just when you thought Jupiter's icy moon Europa couldn't possibly get more interesting, it does. Scientists have announced that the celestial body might in fact have giant moving tectonic plates. As they wrote in their paper published in Nature Geoscience, that could make it "the only Solar System body other than Earth to exhibit a system of plate tectonics."
Using high-resolution images collected by NASA's Galileo spacecraft between 1995 and 2003, geologist Simon Kattenhorn and planetary scientist Louise Prockter studied a specific region of Europa that was lucky enough to have been photographed in-depth by the spacecraft.
Having scrutinized the images, the team suggested the existence of "a thin (~several km) brittle lid overlying a thicker, convecting ice layer with plate motions and subduction restricted to the brittle lid" in an abstract presented at the 45th Lunar and Planetary Science Conference earlier this year.
To put it simply, Kattenhorn and Prockter suggest a form of plate tectonics on Europa whereby a thin surface layer of ice slides around on a slightly warmer and far more fluid section of ice. When one of these plates collides with another, the surface plate is forced downwards. As the plate dives further from the surface it begins to melt and therefore fuses with this warmer, convecting layer.
"Europa may be the only Solar System body other than Earth to exhibit a system of plate tectonics."
Among evidence they found for this was the apparent removal of 20,000km squared patch of Europa's surface. Their tectonic theory could explain where it went.
Placing this study in the wider context of what we already know about Europa paints a fascinating picture of how the moon's ice-covered surface could be connected with its subterranean ocean. The proposition of tectonic plates proposes a highway within which minerals and salts could travel from the surface of the moon down to the ocean and back again.
Yet without high-resolution images from other areas of Europa, scientists cannot ascertain whether similar forms of subduction are taking place all over its surface—which is another reason we desperately need a mission to visit Europa.
As one of the solar system's most fascinating moons, not least because there's a chance life could exist beneath its surface, Europa represents an uncharted icy bastion of potential scientific discovery. This theory of tectonic plates comes less then a year after water vapour was discovered being ejected from Europa's south pole.
The question that now faces NASA is what kind of mission would be best suited to exploring such discoveries.
In March of this year, NASA set aside 15 million dollars for "pre formulation work for a potential mission" to Europa. Leading the way in a potential mission to Europa is the Jet Propulsion Laboratory, which has proposed a concept design, dubbed the Europa Clipper, that would put a spacecraft in orbit around the moon. To protect it from radiation damage, the probe would be put into an eccentric orbit, which would allow it to examine Europa during close fly-bys.
But there's a catch. The Clipper comes with an estimated two billion dollar price tag, which during a time of NASA budget cuts seems rather unappealing. Hope nevertheless remains for a lower budget Europa-bound mission, with NASA calling for a mission that would come in at less than $1 billion.
There's also some promising talk within the US political establishment. In April, a subcommittee of the House Appropriations Committee allocated NASA's planetary-science division, which is working on concept studies for a Europa mission, millions of dollars more than the White House requested for 2015.
And as more discoveries like this are made, the list of reasons to get a mission off the ground only grows longer.