This moon’s surface slides, just like Earth’s

Europa, one of Jupiter’s moons, looks nothing like Earth. It has an icy surface covered with cracks and ridges. But a new study finds that Europa shares at least one feature with our home planet. Its surface slides around, ferried by tectonic plates. In this case, the plates are huge slabs of ice that fit together like giant pieces of a jigsaw puzzle.

Planetary scientist Simon Kattenhorn works at the University of Idaho in Moscow. On many moons in our solar system, he notes, features such as volcanoes or geysers shape the surface. But the new study is the first to find drifting plates on a foreign world, he told Science News. “We’ve found another body in the solar system with plate tectonics. This tells us that this process can happen on more than just rocky planets like Earth.” 

Kattenhorn worked on the new study with Louise Prockter of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

Many scientists believe Europa could be a good place to look for extraterrestrial life because it has an ocean of liquid water beneath its icy surface. The moon’s shifting plates may help ferry nutrients from the surface to the ocean, Kattenhorn says. That kind of motion boosts scientists’ hopes of finding marine life there.

Indeed, finding plate tectonics “is very exciting,” astrobiologist Britney Schmidt told Science News. Astrobiologists study life, wherever it may thrive — including on other planets. She says that tectonics heighten “Europa’s chances for supporting life.” Schmidt, who works at Georgia Tech University in Atlanta, did not take part in the new study.

How the motion was found

Two years ago, Kattenhorn and Prockter spotted something odd on Europa. They’d been studying maps of the moon taken in 1998 by Galileo, a NASA spacecraft. They noticed that criss-crossing ridges on Europa didn’t line up. A swath of the moon’s surface looked as though a piece had been torn out of it, with another piece laid on top.

This mismatch marks the spot where two giant slabs collided, the researchers propose in the September 7 Nature. One of those slabs is sliding beneath the other. The sinking slab submerges into Europa’s interior and combines with warmer interior ice, the researchers suggest. A similar event happens in a subduction zone on Earth. In that case, one slab of the planet’s rocky crust slides beneath another, where it eventually melts and is recycled.

Kattenhorn and Prockter measured the intersection of the two segments. It appears to be more than 1,700 kilometers (1,100 miles) long. In their study, they suggest that similar segments may cover Europa’s entire surface.

Their finding may help explain a puzzle about this moon. It formed more than 4 billion years ago with the rest of the solar system. However, the moon’s surface is only 40 million to 90 million years old. Astronomers have long wondered why it appears so young.

The new study suggests older segments of the surface slid down into Europa’s subsurface ocean. By the researcher’s estimate, Europa’s entire surface may renew itself at least once every 90 million years.

“We now have a mechanism that explains the young surface,” Kattenhorn told Science News.

Schmidt, at Georgia Tech, says the timing of the new finding couldn’t be better. NASA has proposed sending a spacecraft to Europa in 2022.

“Everything we’ve discovered about Europa makes it more and more Earth-like and exciting for the potential of life beyond our planet,” she says. “This research shows we need to go back to Europa and we should to go back soon.”

Power Words

astrobiology  The study of life everywhere in the universe, including on Earth and in space.

astronomy    The area of science that deals with celestial objects, space and the physical universe as a whole. People who work in this field are called astronomers.

Europa  One of the moons of Jupiter and the sixth-closest satellite to the planet. Europa, 1,951 miles across, has a network of dark lines on a bright, icy surface

extraterrestrial  Anything of or from regions beyond Earth.

Jupiter  (in astronomy) The solar system’s largest planet, it has the shortest day length (10 hours). A gas giant, its low density indicates that this planet is composed of light elements, such as hydrogen and helium. This planet also releases more heat than it receives from the sun, as gravity compresses its mass (and slowly shrinks the planet).

marine  Having to do with the ocean world or environment.

moon  The natural satellite of any planet.

NASA   (short for National Aeronautics and Space Administration)Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It has also sent research craft to study planets and other celestial objects in our solar system.

solar system  The eight major planets and their moons in orbit around the sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

subduction zone    A large fault where one tectonic plate sinks beneath another as they collide.  Subduction zones usually have a deep trench along the top

tectonic plates  Gigantic slabs — some spanning thousands of kilometers (or miles) across — that make up Earth’s outer layer. Now it appears an ice analog of these plates exists on the surface of Jupiter’s moon Europa.

volcano  A place on Earth’s crust that opens, allowing magma and gases to spew out from the mantle. The magma rises through a system of pipes or channels, sometimes spending time in chambers where it bubbles with gas and undergoes chemical transformations. This plumbing system can become more complex over time. This can result in a change, over time, to the chemical composition of the lava as well. The surface around a volcano’s opening can grow into a mound or cone shape as successive eruptions send more lava onto the surface, where it cools into hard rock.