PULLMAN, Wash.—A recent study by geophysicists at Washington State University offers insight into how nutrients may reach the subsurface ocean of Europa, one of Jupiter's moons and a leading candidate for extraterrestrial life in the solar system.
Scientists have long wondered how life-sustaining nutrients could make it from the surface into Europa's ice-covered ocean, where microscopic life is believed to exist. Drawing from a process from Earth's geology known as crustal delamination, the research team used computer modeling to show that dense, nutrient-rich ice can separate from the surrounding ice and descend into the ocean.
"This is a novel idea in planetary science, inspired by a well-understood idea in Earth science," said Austin Green, lead author and postdoctoral researcher at Virginia Tech. "Most excitingly, this new idea addresses one of the longstanding habitability problems on Europa and is a good sign for the prospects of extraterrestrial life in its ocean."
The research paper was published in The Planetary Science Journal by Green, who conducted much of the primary research during his doctoral dissertation at WSU, and Catherine Cooper, associate professor of geophysics in the School of Environment and associate dean in the College of Arts and Sciences.
Europa contains more liquid water than all of Earth's oceans combined, but its global ocean lies beneath a thick shell of ice that blocks sunlight. The icy shell means that any life in Europa's ocean has to find nutrient and energy sources other than the Sun, raising longstanding questions about how Europa's ocean could be habitable.
Europa is also constantly bombarded by intense radiation from Jupiter. The radiation interacts with salts and other materials on Europa's surface to form useful nutrients for oceanic microbes. Although there are several theories, scientists are unsure of how that nutrient-rich surface ice can work through the icy shell layer to reach the ocean layer. While Europa's icy surface is highly geologically active due to Jupiter's gravitational pull, the ice mostly shifts side to side rather than in the downward motion necessary for surface-ocean exchange.
Green and Cooper decided to look to Earth for possible explanations and solutions to the surface recycling problem. They zeroed in on the concept of crustal delamination, where a zone of crust is tectonically squeezed and chemically densified until it detaches and sinks into the mantle.
The researchers thought this concept might apply to Europa, since various regions of the ice surface are enriched in densifying salts. Other studies have shown that ice crystalline structure is weakened by included impurities and is less stable than pure ice. However, to trigger delamination, the ice surface needs to be weakened in order to detach and sink within the icy shell interior.
The research team proposed that the denser, saltier ice surrounded by pure ice would sink into the interior of the ice shell, providing a means of recycling Europa's surface and feeding the ocean. Using computer modeling, they determined that nutrient-rich surface ice can sink all the way to the base of the ice shell for almost any salt content, provided there is at least a little weakening in the surface ice. The process is also relatively rapid and could be a consistent means of recycling ice and providing nutrients into Europa's ocean.
The findings closely align with the primary goals of the Europa Clipper, a NASA flagship mission launched in 2024 to investigate Europa's ice shell, ocean, and potential to support life using a suite of scientific instruments.
This research effort was supported in part by the National Aeronautics and Space Administration (NASA) Grant NNX15AH91G, and used resources from the Center for Institutional Research Computing at Washington State University.
