Researchers have found evidence that Jupiter’s moon Europa could have tectonic plates, making it the only world found to date that has geological features just like Earth.
By scrutinising images of the large moon fetched by NASA’s Galileo spacecraft back in the early 2000s, a pair of planetary scientists – University of Idaho’s Simon Kattenhorn and Louise Prockter of the John Hopkins University Applied Physics Laboratory – have found some unusual geological boundaries on the Galilean moon, which strongly point to plate tectonics. On our planet, we recognise these as jigsaw pieces of the Earth’s crust, which make mountainous peaks and volcanoes and that trigger the earthquakes that shake the ground beneath our feet.
Currently, we have clear visual evidence that Europa’s icy crust is expanding, with its surface being riddled with cracks and ridges. Plates thought to be shifting around on this frozen world have been likened to the movement of plates either side of San Andreas fault, which rub against each other in California. Large gaps where Earth’s surface has been torn apart – just like Europa’s icy surface – can also be found across Europe.
In some regards though, Europa’s crust seems to be different with planetary scientists scratching their heads over the moon’s expanding icy crust for years. They have struggled to find areas where the old crust was destroyed to make room for the new, but Kattenhorn and Prockter think they might have made some headway in solving the mystery.
“We have been puzzled for years as to how all this terrain could be formed, but we couldn’t figure out how it was accommodated,” says Prockter. “We finally think we’ve found the answer.”
By reconstructing the moon’s plates into their original configuration to get an idea of what the surface looked like before the destruction, Prockter and Kattenhorn quickly realised that almost 20,000 square kilometres (more than 12,000 square miles) of the moon’s surface seemed to be missing in Europa’s northern latitudes.
The team’s findings suggest that this missing terrain is likely to have slid under a second surface plate – which very commonly happens with Earth’s tectonic plates. Both Prockter and Katternhorn could visualise ice volcanoes on the overriding plate, most likely made when the slab drove into the surface beneath it. This means that material is likely to have been forced into the interior rather than being crumpled up as the plates crashed into each other.
It’s likely that this subducted area sunk into the Europa’s ice shell, which we currently understand to be up to 30 kilometres (20 miles thick), rather than breaking through into the moon’s ocean underneath.
“Europa may be more Earth-like than we imagined, if it has a global plate tectonic system,” Kattenhorn says. “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.”