Scientists say they have evidence the surface on Jupiter's moon Europa has been shaped through plate tectonics, the same type of surface-shifting geological activity that's molded the face of Earth.

New research revealed that, while Europa's icy crust appears to be expanding, there weren't any locations on the moon where old crust appeared to be destroyed in the process.

Then, as they were studying images of Europa capured by the National Aeronautics and Space Administration's unmanned orbiter Galileo in the early 2000s, planetary geologists Simon Kattenhorn, of the University of Idaho, Moscow, and Louise Prockter, from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, spotted some geological boundaries on the moon that look more than a little familiar.

"We have been puzzled for years as to how all this new terrain could be formed, but we couldn't figure out how it was accommodated," Prockter in a space agency news release.

"We finally think we've found the answer, she said: Plate tectonics.

The team's results have appeared in the online edition of the journal Nature Geoscience.

Based on a scientific notion that the earth's outer crust is actually a collection of plates, or blocks, that shift against and often overtake one another, plate tectonic theory explains the formation of mountain and volcanoes and the reasons for earthquakes.

It was previously determined surface blocks on Europa -- which is slightly smaller than Earth's moon, but is one of Jupiter's four largest natural satellites -- moved similarly to Earth's surface shift along the side of the San Andreas fault in California.

Many parts of Europa's surface show evidence of extension, where zones many miles wide were formed, as the surface ripped apart and fresh icy material from the underlying shell moved into the newly created void -- like what happens during seafloor spreading here, where new surface material is along mid-ocean ridges and old material is ground up at subduction zones, where two tectonic plates converge and overlap as one is forced under the other.

Still, despite the clear signs of extension on Europa's surface, researchers were not able to figure out how the surface could accommodate all the new material.

When Kattenhorn and Prockter attempted to calculate the original configuration of the chunks of icy terrain seen in Galileo's images of the moon, they discovered more than 12,000 square miles of the surface were missing in Europa's's high northern latitudes.

Further evidence led them to suspect the missing material had slid under a second surface plate -- the emergence of ice volcanoes on the overriding plate, possibly formed through the melting and absorption of the former slab as it was thrust below the surface, and a lack of mountains at the subduction zone, which suggested material was pushed into the interior of the moon instead of rather than being crumpled where the two surface black met.

All that said, Kattenhorn and Prockter concluded the subducted surface material was absorbed into Europa's ice shell, estimated to range up to 20 miles thick, and didn't reach into the underlying ocean.

"Europa may be more Earth-like than we imagined, if it has a global plate tectonic system," Kattenhorn said. "Not only does this discovery make it one of the most geologically interesting bodies in the solar system, it also implies two-way communication between the exterior and interior -- 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."

In July, NASA issued a call for proposed science instruments that could be carried aboard a future mission to Europa.

"Europa continues to reveal itself as a dynamic world with compelling similarities to our own planet Earth," said Curt Niebur, Outer Planets program scientist at NASA Headquarters in Washington. "Studying Europa addresses fundamental questions about this potentially habitable icy moon and the search for life beyond Earth."

Launched in 1989, NASA's Galileo spacecraft was the only space mission to make repeated visits to Europa, passing near the moon about a dozen times.

The mission officially ended when Galileo plunged into Jupiter's atmosphere in September 2003 -- to prevent any possible impact with Europa.