Bizarre Underwater Snow Gives Clues About the Icy Shell of Jupiter’s Moon Europa

Below the thick icy crust of

An illustration of NASA’s Europa Clipper spacecraft flying by Jupiter’s moon Europa. The spacecraft, which is planned to launch in 2024, will carry an ice-penetrating radar instrument developed by scientists at the University of Texas Institute for Geophysics. Credit: NASA/JPL-Caltech

“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 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. 

Europa is a rocky world that is surrounded by a global ocean and a miles-thick ice shell. It is about the size of the Earth’s moon. Previous research indicates the temperature, pressure, and salinity of Europa’s ocean nearest to the ice is similar to what you would find beneath an ice shelf in Antarctica.

Knowing this, the current research investigated the two distinct processes by which water freezes under ice shelves: congelation ice and frazil ice. Congelation ice grows directly from under the ice shelf. Frazil ice forms as ice flakes in supercooled seawater which float upwards through the water, settling on the bottom of the ice shelf.

Both ways make ice that’s less salty than seawater. When scaled up to the size and age of Europa’s ice shell, Wolfenbarger found that the ice would be even less salty. Moreover, according to her calculations, frazil ice – which keeps only a tiny fraction of the salt in seawater – could be very common on Europa. That could mean its ice shell might be orders of magnitude purer than previous estimates. This difference affects everything from its strength, to how heat moves through it, and forces that might drive a kind of ice tectonics.

“This paper is opening up a whole new batch of possibilities for thinking about ocean worlds and how they work,” said Steve Vance, a research scientist at

“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,” he said.

Reference: “Ice Shell Structure and Composition of Ocean Worlds: Insights from Accreted Ice on Earth” by Natalie S. Wolfenbarger, Jacob J. Buffo, Krista M. Soderlund and Donald D. Blankenship, 25 July 2022, Astrobiology.
DOI: 10.1089/ast.2021.0044

Wolfenbarger is currently pursuing a doctoral degree 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.