There Might be Volcanoes at the Bottom of Europa’s sub-ice Oceans

In about three years, NASA plans to launch a robotic orbiter that will study Jupiter’s mysterious moon Europa. It’s called the Europa Clipper mission, which will spend four years orbiting Europa to learn more about its ice sheet, interior structure, chemical composition, and plume activity. In the process, NASA hopes to find evidence that will help resolve the ongoing debate as to whether or not Europa harbors life in its interior.

Naturally, scientists are especially curious about what the Clipper mission might find, especially in Europa’s interior. According to new research and modeling supported by NASA, it’s possible that volcanic activity occurred on the seafloor in the recent past – which could be happening still. This research is the most detailed and thorough 3D modeling on how internal heat is produced and transferred and what effect this will have on a moon.

The research, which was published recently in Geophysical Research Letters, was also presented at the 52nd Lunar and Planetary Science Conference, which was held virtually from March 15th to 19th. The team responsible was led by geophysicist Marie Behounkova Charles University in the Czech Republic, who was joined by researchers from the Laboratoire de Planétologie et Géodynamique at the University of Nantes and NASA’s Jet Propulsion Laboratory (JPL).

Radiation from Jupiter can destroy molecules on Europa’s surface. Material from Europa’s ocean that ends up on the surface will be bombarded by radiation, possibly destroying any biosignatures, or chemical signs that could imply the presence of life. Credit: NASA/JPL-Caltech

Ever since the Voyager 1 and 2 and passed through the Jupiter systems in 1979, scientists have speculated that there might be an ocean lurking beneath Europa’s icy crust. Since then, multiple lines of evidence have emerged that confirm this theory, from data on the moon’s magnetic field to plume activity on its surface. To break it down, they theorized that Europa’s interaction with Jupiter’s powerful gravitational pull causes tidal flexing in its interior.

This flexing generates energy, which is converted to heat and slowly leaked from the core (composed of iron-nickel and silicate minerals) into the icy mantle, leading to hydrothermal vents and a warm-water ocean. Beyond allowing for an interior ocean, scientists have also speculated for decades that Europa may also experience volcanic activity at its core-mantle boundary in a way that is similar to Jupiter’s moon Io.

As the innermost of Jupiter’s largest satellites, Io experiences intense tidal flexing in its interior, which is why it is covered by hundreds of volcanoes. These eject lava, volcanic gas, and dust up to 400 km (250 mi) from the surface, which is then charged by Jupiter’s magnetic field to create a torus of energized plasma. This plasma is linked to the intense auroral activity in Jupiter’s upper atmosphere.

Since Europa is farther away than Io is from its host planet, scientists have naturally wondered if the effect of tidal flexing would be enough to generate volcanic activity beneath the moon’s icy surface. Now, the models created by Behounkova and her colleagues have shown that there may be enough heating to partially melt the rocky layer at the core-mantle boundary, resulting in volcanic activity on the ocean floor.

Graphic showing how volcanism in Europa’s interior works. Credit: NASA/JPL-Caltech/Michael Carroll

B?hounková and her colleagues further predicted that volcanic activity is most likely to occur near Europa’s poles, which is where the most heat is generated in the interior. Perhaps most significantly, they looked at how this volcanic activity may have evolved over time, as long-lived energy sources are more likely to lead to the emergence of life. Volcanoes, if present, could be what is powering hydrothermal systems like those that are found on the ocean floor here on Earth.

Around these hydrothermal vents, the interaction of hot magma with seawater created abundant chemical energy that provides lifeforms with the energy they need to power their metabolism (rather than sunlight). In fact, there are many scientists who speculate that life emerged around hydrothermal vents on the ocean floor billions of years ago. On Europa, a similar mechanism could provide life forms with energy since they also have no access to sunlight. As Behounkova said in a recent press release from NASA JPL:

“Our findings provide additional evidence that Europa’s subsurface ocean may be an environment suitable for the emergence of life. Europa is one of the rare planetary bodies that might have maintained volcanic activity over billions of years, and possibly the only one beyond Earth that has large water reservoirs and a long-lived source of energy.”

When it reaches its destination by 2030, the Europa Clipper will measure the moon’s gravity and magnetic field for signs of anomalies. These could be an indication of the subsurface volcanic activity that was predicted by this new research, especially around the poles. To be fair, the Clipper orbiter is not designed for astrobiology, an interdisciplinary field of research that studies conditions that are associated with life on extraterrestrial bodies.

Nevertheless, its detailed reconnaissance of Europa will allow astrobiologists to place tighter constraints on Europa’s habitability. “The prospect for a hot, rocky interior and volcanoes on Europa’s seafloor increases the chance that Europa’s ocean could be a habitable environment,” said Robert Pappalardo, a Project Scientist for the Europa Clipper mission at NASA JPL. “We may be able to test this with Europa Clipper’s planned gravity and compositional measurements, which is an exciting prospect.”

Beyond narrowing the search for extraterrestrial life, understanding Europa’s habitability will help scientists to better understand how life developed on Earth. Similar missions sent to other “Ocean Worlds” like Ganymede, Titan, Enceladus, and Triton, are likely to yield equally valuable insight into whether or not they can support life. Beyond addressing the mystery of life’s origins, this data could also point the way towards life on extrasolar planets.

Who knows? It may very well be that “Ocean Worlds” (and not rocky planets) are the best place to look for life in the Universe.

Further Reading: NASA, Geophysical Science Letters