In about three years, NASA plans to launch a robotic orbiter to investigate the mysterious Jupiter moon Europa. It’s called the Europa Clipper Mission, which will orbit Europe for four years to learn more about its ice sheet, internal structure, chemical composition, and plume activity. In doing so, NASA hopes to find evidence that will help resolve the ongoing debate over whether Europe has life within it.
The scientists are of course particularly curious about what the Clipper mission could find, especially in the interior of Europe. According to new research and models backed by NASA, it is possible that volcanic activity has occurred on the ocean floor in the recent past – which could still happen. This research is the most detailed and thorough 3-D modeling of how internal heat is created and transferred, and what effect this has on a moon.
The research, recently published in Geophysical Research Letters, was also featured at the 52nd Lunar and Planetary Science Conference, held virtually March 15-19. The responsible team was led by the geophysicist Marie Behounkova Charles University in the Czech Republic, supported by researchers from the Laboratoire de Planétologie et Géodynamique at the University of Nantes and the Jet Propulsion Laboratory (JPL) at NASA.
The radiation from Jupiter can destroy molecules on the surface of Europe. Material from Europe’s ocean that lands on the surface is bombarded with radiation, potentially destroying any biosignatures or chemical signs that could indicate the presence of life. Photo credit: NASA / JPL-Caltech
Ever since Voyager 1 and 2 passed the Jupiter systems in 1979, scientists have speculated that an ocean might lurk beneath Europe’s icy crust. Since then, several lines of evidence have emerged to confirm this theory, from data on the moon’s magnetic field to plume activity on its surface. To break it down, they theorized that Europe’s interaction with the strong pull of Jupiter was causing tides inside it.
This bending creates energy that is converted into heat and slowly escapes from the core (made up of iron-nickel and silicate minerals) into the icy mantle, resulting in hydrothermal springs and a warm water ocean. Aside from considering an inner ocean, scientists have speculated for decades that Europe could experience volcanic activity similar to Jupiter’s moon Io at its core-mantle boundary as well.
As the innermost of the largest Jupiter satellites, Io experiences a strong tidal bending inside, which is why it is covered by hundreds of volcanoes. These eject lava, volcanic gas, and dust up to 250 miles (400 km) from the surface, which are then charged by Jupiter’s magnetic field to create a torus of energized plasma. This plasma is associated with the intense aurora activity in Jupiter’s upper atmosphere.
Naturally, with Europe being further away than Io from its host planet, scientists have wondered whether the effect of the tidal bending 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 warming to partially melt the rock layer at the core-mantle boundary, leading to volcanic activity on the ocean floor.
Graphic showing how volcanism works in the interior of Europe. Photo credit: NASA / JPL-Caltech / Michael Carroll
B? Hounková and her colleagues also predicted that volcanic activity was most likely to occur near the poles of Europe, where most of the heat is generated inside. Perhaps most importantly, they were studying how this volcanic activity might have evolved over time, since long-lived sources of energy are more likely to lead to the creation of life. Volcanoes, if any, could be the engine for hydrothermal systems such as those found on the ocean floor here on earth.
Around these hydrothermal springs, the interaction of hot magma with sea water created abundant chemical energy that provides life forms with the energy they need to metabolize (rather than sunlight). In fact, many scientists speculate that life arose around hydrothermal springs on the ocean floor billions of years ago. In Europe, a similar mechanism could supply life forms with energy, since they also have no access to sunlight. As Behounkova recently said in a NASA JPL press release:
“Our results provide additional evidence that Europe’s subterranean ocean could be a suitable environment for life to emerge. Europe is one of the rare planetary bodies that may have sustained volcanic activity for billions of years, and possibly the only one outside of Earth that has large reservoirs of water and a long-lived source of energy. “
When it reaches its destination in 2030, the Europa Clipper will measure the moon’s gravity and magnetic field for signs of anomalies. This could be an indication of the underground volcanic activity predicted by this new research, particularly around the poles. To be fair, the Clipper orbiter is not designed for astrobiology, an interdisciplinary field of research that studies conditions associated with life on alien bodies.
Nonetheless, his detailed exploration of Europe will allow astrobiologists to further constrain Europe’s habitability. “The prospect of a hot, rocky interior and volcanoes on Europe’s seabed increases the chance that Europe’s ocean could be a habitable environment,” said Robert Pappalardo, a project scientist for the Europa Clipper mission at NASA JPL. “We can potentially test this with the planned gravity and composition measurements from Europa Clipper, which is an exciting prospect.”
Aside from restricting the search for extraterrestrial life, understanding Europe’s habitability will help scientists better understand how life on Earth evolved. Similar missions sent to other “ocean worlds” such as Ganymede, Titan, Enceladus, and Triton are likely to provide valuable insights into whether or not they can support life as well. Beyond the mystery of the origin of life, these data could also point the way to life on extrasolar planets.
Who knows? It may very well be that “ocean worlds” (rather than rocky planets) are the best place to look for life in the universe.
Further reading: NASA, Geophysical Science Letters