Beneath Europa’s thick icy crust is a massive global ocean where snow floats upward over inverted ice peaks and submerged ravines. The strange underwater snow is known to occur beneath Earth’s ice shelves, but a new study shows that the same is likely true on Jupiter’s moon, where it may play a role in building its ice shell.
Underwater snow is much purer than other types of ice, which means Europa’s ice shell could be much less salty than previously thought. That’s important to mission scientists preparing NASA’s Europa Clipper spacecraft, which will use radar to peer beneath the ice shell to see if Europa’s ocean might be hospitable to life. The new information will be critical because salt trapped in the ice can affect what and how deep in the ice shell the radar will see, so being able to predict what the ice is made of will help scientists make sense of the data.
The study, published in the August issue of the journal Astrobiology, was led by the University of Texas at Austin, which is also leading the development of Europa’s Clipper ice-penetrating radar instrument. Knowing what kind of ice Europa’s shell is made of will also help decipher the salinity and habitability of its ocean.
“When we’re exploring Europa, we’re interested in the salinity and composition of the ocean, because that’s one of the things that will govern its potential habitability or even the kind of life that could live there,” the author said principal of the study. Natalie Wolfenbarger, a graduate student researcher at the University of Texas Institute for Geophysics (UTIG) at the UT Jackson School of Geosciences.
Europa is a rocky world about the size of Earth’s moon that is surrounded by a global ocean and a shell of ice kilometers thick. Previous studies suggest that the temperature, pressure and salinity of Europa’s ocean closest to the ice is similar to what you would find under an ice shelf in Antarctica.
Armed with this knowledge, the new study examined the two different ways in which water freezes under ice shelves, freezing ice and frazil ice. Freezing ice grows directly under the ice shelf. Frazil ice forms as ice flakes in supercooled seawater that float up through the water and settle on the bottom of the ice shelf.
Both ways make the ice less salty than seawater, which Wolfenbarger found would be even less salty when scaled up to the size and age of Europa’s ice shell. Also, according to their calculations, frazil ice, which holds only a small fraction of the salt in seawater, could be very common in Europe. This means that its ice shell could be orders of magnitude purer than previous estimates. This affects everything from its strength, to how heat moves through it, and the forces that can drive a kind 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 research scientist at NASA’s Jet Propulsion Laboratory (JPL) who was not involved in the study. “It sets the stage for how we might prepare for the Europa Clipper ice analysis.”
According to co-author Donald Blankenship, UTIG principal investigator and principal investigator of the Europa Clipper ice-penetrating radar instrument, the research is validation for using Earth as a model for understanding Europa’s habitability.
“We can use Earth to assess the habitability of Europa, measure the exchange of impurities between the ice and the ocean, and find out where the water is in the ice,” he said.
Wolfenbarger is currently pursuing a PhD in geophysics at the UT Jackson School and is a graduate student affiliate member of the Europa Clipper science team.
The research was funded by the G. Unger Vetlesen Foundation and the Zonta International Amelia Earhart Fellowship.
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