Europa’s ice shell could be much less salty than previously thought, study

Underwater snow gives clues about Europa’s icy shell.

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Unlike Earth, Europa’s ocean lies below a shell of ice probably 15 to 25 kilometers thick. The snow within the ocean floats upwards onto inverted ice peaks and submerged ravines.

On Earth, the bizarre underwater snow is known to occur below ice shelves on Earth, but a new study shows the same for Jupiter’s moon Europa. The study suggests that underwater snow may play a vital role in building ice shells.

Since underwater snow is significantly more pure than other types of ice, Europa’s ice shell may not be as salty as initially believed.

This is crucial information for the mission scientists prepping NASA’s Europa Clipper probe, which will use radar to peer beneath the ice shell to determine whether Europa’s ocean may support life. The ability to predict what the ice is made of will help scientists make sense of the data since salt trapped in the ice can alter what and how far the radar will see into the ice shell.

The study’s lead author Natalie Wolfenbarger, a graduate student researcher at the University of Texas Institute for Geophysics (UTIG) in the UT Jackson School of Geosciences, said, “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 type of life that might live there.”

According to earlier research, the temperature, pressure, and salinity of the water closest to the ice on Europa are comparable to those found beneath an Antarctic ice shelf.

Knowing this, the new study investigated the two distinct processes by which water freezes beneath ice shelves: congelation ice and frazil ice. Ice that is congealing grows out from beneath the ice shelf. Frazil ice is created when ice crystals in supercooled saltwater float upward through the ocean and land on the ice shelf’s base.

Both methods result in ice with a salt content lower than seawater, which, according to Wolfenbarger, would be considerably lower when scaled up to the size and age of Europa’s ice shell. Scientists also calculated that frazil ice, which only retains a minuscule portion of the salt in saltwater, may be widespread on Europa. This implies that its ice shell may be much purer than previously thought. Its strength, the flow of heat through it, and potential ice tectonic forces are all impacted by this.

Steve Vance, a research scientist at NASA’s Jet Propulsion Laboratory (JPL) who was not involved in the study, said, “This paper is opening up a whole new batch of possibilities for thinking about ocean worlds and how they work. It sets the stage for how we might prepare for Europa Clipper’s analysis of the ice.”

According to co-author Donald Blankenship, a senior research scientist at UTIG and principal investigator for Europa Clipper’s ice-penetrating radar instrument, the research is validation for using the Earth as a model to understand the habitability of Europa.

“We can use Earth to evaluate Europa’s habitability, measure the exchange of impurities between the ice and ocean, and figure out where water is in the ice.”

Journal Reference:

  1. Natalie S. Wolfenbarger et al., Ice Shell Structure and Composition of Ocean Worlds: Insights from Accreted Ice on Earth, Astrobiology (2022). DOI: 10.1089/ast.2021.0044
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