The surface of Jupiter's moon Europa likely experienced a dramatic shift within the last tens of million years, a new study suggests. Its poles are not where they used to be, and features on its surface indicate it rotated about 70 degrees with respect to its rotational axis. The surface is about 50 million years old and researchers expect it to shift over the course of about 12 million years. Known as a true polar wander, this requires the icy surface of Europa to be completely separated from the rocky interior, resting exclusively on an ocean.
The evidence for this, reported in Geophysical Research Letters, comes from maps of its surface by NASA’s Galileo and Voyager probes. The surface of Europa is marked with concentric fractures that the team believes could only be caused by a true polar wander. These deep fissures in the ice, some 1 to 2 kilometers (0.6 to 1.2 miles) across and 200 meters (660 feet) deep, also cross recent major craters, which strongly suggests the event happened in the last few million years.
“Our key finding is that the fractures associated with true polar wander on Europa cross-cut all terrains. This means that the true polar wander event is very young and that the ice shell and all features formed on it have moved more than 70 degrees of latitude from where they first formed,” lead author Dr Paul Schenk, from the Lunar and Planetary Institute, said in a statement. “If true, then the entire recorded history of tectonics on Europa should be reevaluated.”
This hypothesis is certainly intriguing and the researchers go a step further to discuss several testable predictions that a true polar wander would create on such a celestial body.
"In addition to generating global-scale tectonic features, true polar wander also produces global-scale gravity and shape perturbations, which affects gravity and shape constraints on the interior structure," said co-investigator Isamu Matsuyama from the University of Arizona.
To investigate those predictions, we’ll have to wait for another close-up study of Europa. Luckily, NASA’s Europa Clipper and the European Space Agency’s JUICE missions will return to the sixth-largest moon in the Solar System sometime between the end of this decade and the beginning of the next.