Study Sheds More Light on Icy Shells of Europa and Other Ocean Worlds

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Study Sheds More Light on Icy Shells of Europa and Other Ocean Worlds
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The underwater snow is known to form in low temperature environments, e.g., beneath ice shelves, on Earth. New research led by University of Texas at Austin planetary researchers shows that the same is likely true for ocean worlds such as Jupiter’s moon Europa, where it may play a role in building its ice shell.

The surface of Europa looms large in this newly-reprocessed color view; image scale is 1.6 km per pixel; north on Europa is at right. Image credit: NASA / JPL-Caltech / SETI Institute.

The surface of Europa looms large in this newly-reprocessed color view; image scale is 1.6 km per pixel; north on Europa is at right. Image credit: NASA / JPL-Caltech / SETI Institute.

“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,” said lead author Natalie Wolfenbarger, a researcher with the Institute for Geophysics at the University of Texas at Austin.

Europa, the sixth of Jupiter’s moons and the fourth largest, is about the size of the Earth’s Moon.

This world is believed to hide an ocean of salty liquid water beneath its frozen surface.

Previous studies suggested the temperature, pressure and salinity of Europa’s ocean nearest to the ice is similar to what is found beneath an ice shelf in Antarctica.

Armed with that knowledge, Wolfenbarger and her colleagues from the University of Texas at Austin and Dartmouth College examined two classes of accreted ice found on Earth: congelation ice and frazil ice.

Congelation ice grows directly from under the ice shelf. Frazil ice forms as ice flakes supercooled water which float upwards through the water, settling on the bottom of the ice shelf.

Both ways make ice that’s less salty than seawater, which the researchers found would be even less salty when scaled up to the size and age of Europa’s ice shell.

What’s more, frazil ice — which keeps only a tiny fraction of the salt in seawater — could be very common on Europa.

That means 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 forces that might drive a kind of ice tectonics.

“This research is validation for using the Earth as a model to understand the habitability of Europa,” said senior author Dr. Donald Blankenship, also from the Institute for Geophysics at the University of Texas at Austin.

“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.”

The study appears in the journal Astrobiology.

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Natalie S. Wolfenbarger et al. 2022. Ice Shell Structure and Composition of Ocean Worlds: Insights from Accreted Ice on Earth. Astrobiology 22 (8): 937-961; doi: 10.1089/ast.2021.0044




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