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Underwater snow gives clues to Europa’s icy shell

Beneath the thick icy crust of Europe lies a huge global ocean where snow floats upward on inverted ice peaks and submerged ravines. Bizarre underwater snow is known to occur under ice shelves on Earth, but a new study shows the same is likely true for Jupiter’s moon, where it could play a role in building its shell of ice.

Underwater snow is much purer than other types of ice, which means Europe’s ice shell may be much less salty than previously thought. That’s important for mission scientists preparing NASA’s Europa Clipper spacecraft, which will use radar to peek under the ice shell to see if Europa’s ocean might be hospitable to life. The new information will be essential because the salt trapped in the ice can affect what radar will see in the ice shell and how deep, 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 edition of the journal Astrobiology, was led by the University of Texas at Austin, which is also leading the development of the Europa Clipper ice-penetrating radar instrument. Knowing what type of ice Europa’s shell is made of will also help decipher the salinity and habitability of its ocean.

“When we explore Europa, we are interested in the salinity and the composition of the ocean, because that is one of the things that will govern its potential habitability or even the type of life that could live there,” said l lead author of the study. Natalie Wolfenbarger, graduate student at the University of Texas Institute of Geophysics (UTIG) at UT Jackson School of Geosciences.

Europa is a rocky world the size of Earth’s moon that is surrounded by a global ocean and a kilometer-thick shell of ice. Previous studies suggest that the temperature, pressure and salinity of the European ocean closest to the ice are similar to what you would find under an ice shelf in Antarctica.

Building on this knowledge, the new study looked at the two different ways water freezes under ice shelves, freezing ice and frazil. Freezing ice grows directly under the pack ice. Frazil ice forms as flakes of ice in supercooled seawater that float upwards in the water, settling to the bottom of the pack ice.

Both ways produce ice that is less salty than seawater, which Wolfenbarger says would be even less salty when scaled to the size and age of Europe’s ice shell. Moreover, according to his calculations, frazil ice – which retains only a tiny fraction of the salt in seawater – could be very common on Europa. That means its ice shell could be purer than previous estimates. This affects everything from its strength to the way heat moves through it and the forces that could lead to some 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 researcher at NASA’s Jet Propulsion Laboratory (JPL), who was not involved in the study. “This paves the way for how we might prepare for analysis of the Europa Clipper ice.”

According to co-author Donald Blankenship, principal investigator at UTIG and principal investigator of the Europa Clipper ice-penetrating radar instrument, the research validates the use of Earth as a model to understand the habitability of Europa. .

“We can use Earth to assess the habitability of Europa, measure the exchange of impurities between the ice and the ocean, and determine where the water is in the ice,” he said.

Wolfenbarger is currently pursuing a Ph.D. in geophysics at UT Jackson School and is a graduate student member of the Europa Clipper science team.

The research was funded by the G. Unger Vetlesen Foundation and the Zonta International Amelia Earhart Fellowship.