Jupiter鈥檚 icy moon Europa may not be as ripe for life as previously thought. Its underground ocean has long made it one of the most promising candidates in our solar system to host life, but theoretical studies of its seafloor are putting a damper on its promise.
On Earth, much of the life in the oceans is supported by hydrothermal activity at the seafloor, where water interacts with rock. This activity provides nutrients and energy that are crucial to living organisms, and many researchers have theorised that similar processes could aid life on Europa.
However, these interactions require a regular supply of fresh rock. That supply can come from faults in the rock, or via volcanic activity that lets magma rise from deep underground. Research presented at the Lunar and Planetary Science Conference in Texas on 11 and 12 March suggests that both of those phenomena may be unlikely on Europa.
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鈥淭here鈥檚 been a lot of work done on the outer shell because we can see it鈥� but we don鈥檛 have much information on the seafloor, not surprisingly, because it鈥檚 extremely hard to get to,鈥� said at Washington University in St. Louis, Missouri. Instead of using direct observations, researchers who study Europa鈥檚 seafloor have relied on theoretical calculations, simulations and comparisons to what we see on Earth.
The most dramatic way Europa鈥檚 core could contribute to the habitability of its ocean is via volcanism 鈥� magma from deep underground seeping into the ocean through dikes. at NASA鈥檚 Jet Propulsion Laboratory in California and his colleagues simulated this process, but the dikes were not able to transport magma all the way from the molten areas deep in the core to its edge.
鈥淭hey did really, really, really, really bad,鈥� said Green. 鈥淥ur most successful one was an 11.5-kilometre dike.鈥� That dike would have had to penetrate 227 kilometres of rock to spill magma onto the seafloor. 鈥淚f this volcanism is necessary for habitability, Europa鈥檚 ocean is uninhabitable,鈥� said Green.
The faults in the seafloor don鈥檛 necessarily have to have magma in them to be useful, though. Even empty faults could fuel important water-rock interactions 鈥� but Byrne and his team found that it is incredibly unlikely that any new faults are forming under Europa鈥檚 sea. 鈥淲hat we鈥檙e finding is this big mismatch between stress and strength,鈥� said Byrne. 鈥淚 don鈥檛 think there鈥檚 anything happening at the ocean floor.鈥�
Yet another research group found that even simple erosion by sand is unlikely because the low gravity of a relatively small moon means that the sediment should sit lightly on the seafloor, not providing enough weight to wear it down. 鈥淯nfortunately I鈥檓 kind of adding to the depressing news that maybe the seafloor isn鈥檛 as active as we maybe thought it could be,鈥� said at the University of Texas at Austin, part of that group.
All this does not mean that Europa is completely uninhabitable. 鈥淚 think that what鈥檚 being shown here is that volcanism and habitability models that rely on the interior are starting to be less likely, but I still think that stuff coming through the ice shell from the top down is still a pretty promising avenue of research,鈥� said Green. We won鈥檛 be able to truly search for life on Europa until we can get into the ocean itself, which won鈥檛 be for decades to come.
