Europa’s icy crust found to be at least 20 kilometres thick
The puzzling, fascinating surface of Jupiter's icy moon Europa looms large in this reprocessed color view, made from images taken by NASA's Galileo spacecraft in the late 1990s. Photo: NASA/JPL-Caltech/SETI Institute Scientists are studying Europa, one of Jupiter’s many moons, to see if it could support life. One of the key factors that could determine the likelihood of life on this natural satellite is the structure of the icy moon, which is as old as the Earth.
A new study published in journal Science Advances has estimated Europa’s ice shell to be at least 20 kilometres thick. Europa has a water ice crust, which hides a vast saltwater ocean below. Previous estimates of its ice shell thickness range from only a few kilometres thick up to a few tens of kilometres thick.
These differences in estimates are because scientists used different surface features on Europa, such as ridges, chaos regions, and craters, Shigeru Wakita, a research scientist at Purdue University and one of the study’s authors, told Down To Earth (DTE).
There has been a long debate about the thickness of Europa’s ice shell. “It is important to determine this because the ice shell thickness dictates what processes can occur within the ice,” Brandon Johnson, an associate professor at Purdue University, told DTE.
The thickness of Europa’s ice shell affects how much heat is generated by tides within it, or tidal heating and how materials move between the surface and the ocean underneath, the study said. These factors are crucial for figuring out if the icy moon could support life.
Europa is constantly stretching and flexing from its own orbit, Jupiter’s gravity and the orbits of nearby moons like Io and Ganymede, which creates tidal heating. This process keeps Europa geologically active.
The researchers analysed data and images from National Aeronautics and Space Administration’s (NASA) spacecraft Galileo, which studied Europa in 1998. They specifically looked at impact craters to gain insights into the thickness.
“To form craters on Europa, exogenic material, such as comets, is necessary. The morphology of craters is sensitive to ice shell thickness and structures. Thus, studying their formation is essential to reveal it,” Wakita explained.
The team then relied on numerical simulations to reproduce the formation of the craters and work out the thickness of Europa’s ice shell.
The study suggests that the icy moon’s shell is thick. “When it is thick enough, convection or continual overturn of a portion of the ice shell can occur,” Johnson explained.
A thick ice shell, he added, makes exchange between the ice and ocean more difficult. But other drivers — subduction and cryovolcanism — may still be important processes for exchanging material between the surface and ocean.
Subduction occurs when one of the plates is forced under the other. Europa’s icy plates behave like rocky tectonic plates on Earth.
Cryovolcanism is the eruption of water and other volatiles onto the surfaces of the icy satellites of giant planets.
Johnson expects to find more robust evidence on the ice shell thickness from NASA’s upcoming Europa Clipper mission, which is expected to be launched on October 10, 2024. The mission aims to study whether the icy moon harbours conditions suitable for life.
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