Europa, one of the four large moons of Jupiter, has a surface alive with the motions of icy plate tectonics, according to new findings from the Galileo spacecraft.

On Earth, plate tectonics push rock plates bearing continents on a bed of magma under the crust. As one plate comes in contact with another, old crust can be forced under the other sheet, or rise up as mountains.

Europa's shell of ice is believed to measure 10 to 20 miles thick. One of the plates making up the outer surface of the satellite was observed subducting, or going under, another plate. There, the thick ice sheet melted into water the same way rock melts into magma on Earth. This is the first time this process has been observed on a world other than our own.

An international group of astronomers and other scientists examined data recorded by the Galileo orbiter early in the century. That robotic observatory was launched to the largest planet in the solar system in 1989, arriving in 1995. Researchers examined areas where new ice is rising from beneath the surface of the moon.

"And unless the moon is expanding, which we don't think is the case, you have to remove surface from somewhere else in order to accommodate the new surface area being created," Simon Kattenhorn of the University of Idaho, said.

Louise Prockter, a colleague of Kattenhorn, worked with the researcher to investigate images of Europa stretching over 51,700 square miles. A fragment of ice plate 12,000 square miles in size seemed to disappear in the images recorded by Galileo. Investigators believe the material which was subducted was absorbed in the neighboring ice plate, rather than melting in liquid water lying under the frozen crust.

Mars may have once exhibited plate tectonics, although those processes have ceased over eons.

Europa has one of the youngest surfaces seen anywhere in the solar system, which suggested old crust had to be recycled to make room for new material.

"Europa may be more Earth-like than we imagined, if it has a global plate tectonic system. Not only does this discovery make it one of the most geologically interesting bodies in the solar system, it also implies... a way to move material from the surface into the ocean - a process which has significant implications for Europa's potential as a habitable world," Kattenhorn said.

Recycling of material, combined with radiation from Jupiter, could make areas around plate collisions rich in complex materials. These could prove to be prime places in which primitive, alien life may one day be found.

Discovery of plate tectonics on the surface of Europa was detailed in the journal Nature Geoscience.