Beneath the thick icy crust of Jupiter’s moon Europa lies a vast, global ocean where snow floats upward on upturned ice peaks and sunken ravines. Strange underwater snow is known to occur beneath ice shelves on Earth, but new research suggests the same is likely true on Jupiter’s moons. In fact, it may play a role in building Europa’s ice shell. Underwater snow is much cleaner than other types of ice. This means that Europa’s ice shell could be much less salty than previously thought. That’s critical information for mission scientists preparing NASA’s Europa Clipper spacecraft, which will use radar to scan beneath the ice shell to see if Europa’s ocean could be hospitable to life. The new information is important because salt trapped in the ice can affect what and how deep the radar will see inside the ice shell. Being able to predict what the ice is made of will help scientists make sense of the data. The study was led by the University of Texas at Austin, which is also leading the development of Europa Clipper’s ice-penetrating radar instrument. Knowing what kind of ice Europa’s shell is made of will also help determine the salinity and habitability of its ocean. The study was published in the August issue of the journal Astrobiology. An illustration of NASA’s Europa Clipper spacecraft flying past Jupiter’s moon Europa. The spacecraft, which is scheduled to launch in 2024, will carry an ice-penetrating radar instrument developed by scientists at the University of Texas Geophysics Institute. Credit: NASA/JPL-Caltech “When we explore Europa, we’re interested in the salinity and composition of the ocean, because that’s one of the things that will govern the potential habitability or even the type of life that might live there,” said the study’s lead author. Natalie Wolfenbarger, graduate student researcher at the University of Texas Institute for Geophysics (UTIG) at the UT Jackson School of Geosciences. Europa is a rocky world surrounded by a global ocean and a kilometre-thick ice shell. It is about the size of Earth’s moon. Previous research has shown that the temperature, pressure and salinity of Europa’s ocean closest to the ice is similar to what you’d find under an Antarctic ice shelf. Knowing this, the current research investigated the two distinct processes by which water freezes beneath ice shelves: frozen ice and brittle ice. Permafrost grows directly below the ice shelf. Frazil ice forms as ice flakes in supercooled seawater that float upward through the water, settling to the bottom of the ice shelf. Both ways make ice that is less salty than seawater. When scaled to the size and age of Europa’s ice shell, Wolfenbarger found that the ice would be even less salty. Furthermore, according to her calculations, brittle ice – which retains only a small fraction of the salt in seawater – could be very common in Europa. This could mean that its ice shell may be orders of magnitude cleaner than previously estimated. This difference affects everything from its strength, to how heat moves through it, and the forces that can drive a type of ice tectonics. “This paper opens up a whole new set of possibilities for thinking about ocean worlds and how they work,” said Steve Vance, a researcher at NASA’s Jet Propulsion Laboratory (JPL) who was not involved in the study. “It sets the stage for how we might prepare to analyze Europa Clipper’s ice.” According to co-author Donald Blankenship, the research is validation for using Earth as a model for understanding Europa’s habitability. Blankenship is a senior researcher at UTIG and principal investigator for the Europa Clipper ice-penetrating radar instrument. “We can use Earth to assess Europa’s habitability, measure the exchange of impurities between the ice and the ocean, and figure out where the water is in the ice,” he said. Citation: “Ice shell structure and composition of oceanic worlds: insights from concentrated ice on Earth” by Natalie S. Wolfenbarger, Jacob J. Buffo, Krista M. Soderlund, and Donald D. Blankenship, July 25, 2022, Astrobiology.DOI: 10.1 ast.2021.0044 Wolfenbarger is currently pursuing a PhD in geophysics at the UT Jackson School and is a postgraduate member of the Europa Clipper science team. The research was funded by the G. Unger Vetlesen Foundation and the Zonta International Amelia Earhart Fellowship.
