A mysterious world of water and ice in sight: The ice shell of Jupiter's moon Europa could be formed in part from so-called Frazil ice - "snowflakes" that "trickle" from below onto the deck structures, researchers report. This emerges from comparisons with earthly observations of this process. The special thing about it is that Frazil ice cream is comparatively low in salt. According to this, the ice shell could be "purer" than previously thought, which the scientists say is of considerable importance for research into the potential habitat.
Europa has it all, according to various studies in recent years: It is now assumed that the frosty companion of Jupiter has a huge ocean of liquid salt water under its kilometer-thick ice crust. This has put the celestial body, which is about the size of the moon, at the center of the search for extraterrestrial life forms in our solar system. In view of the amazing adaptability of life on earth, it seems possible that organisms have also developed in the hidden underwater world of Europe. The planned NASA mission “Europa Clipper” should soon provide more information about the mysterious ice moon: A probe is to swing into an orbit around Europa in order to collect various data.
Antarctica as a model
Among other things, it is also planned to analyze the crust using ice-penetrating radar in order to examine its structure and possibly look underneath. Scientists at the University of Texas in Austin are busy developing the corresponding radar device for the Europa Clipper. Basic advance information on what the ice sheet might be like is helpful for performance. In order to obtain clues, the scientists use structures and processes on Earth that could correspond to those on Europa. "We can certainly use Earth to draw inferences about Europe," says senior author Donald Blankenship. Specifically, the focus is on Antarctica: Previous studies indicate that the temperature, pressure and salinity of the water under the ice are similar to those in the case of Jupiter's moon.
As part of their study, the scientists examined the two most important types of growth from below in the Antarctic ice shelf. One form is based on the so-called congelation ice. It is the increment on the existing ice surfaces. The other version is based on the accumulation of so-called Frazil ice. These flakes of ice needles or flakes form in cold seawater and then float upwards. Like snow from below, they settle on the ice surface and are then integrated.
Possibly less salt in the ice
As the scientists report, there is probably only a small temperature gradient under the ice of Europa - the values change only slightly at depth. Under these conditions, in the case of the Antarctic, the formation of Frazil ice occurs particularly intensively, the investigations show. According to the researchers' calculations, a significant part of Europa's ice sheet could also be traced back to the accumulations of underwater snowflakes.
This in turn would be linked to an important aspect, the study shows. Because while congelation ice contains 10 percent of the salt of the surrounding seawater, Frazil ice is much purer and would have only 0.1 percent of the salt of the Europa water from which it forms. This means the ice sheet could be orders of magnitude purer than previously thought. "When researching Europe, we are very interested in salinity because it is a factor with multiple meanings," says lead author Natalie Wolfenbarger. It affects many aspects - from strength to thermal motion to the forces that could drive some type of ice tectonics. The salinity also has practical implications: it affects how the Clipper's radar will penetrate the ice, the scientists point out.
"This work opens up a whole new dimension in looking at distant ocean worlds and the processes that take place within them," comments Steve Vance of NASA's Jet Propulsion Laboratory in Pasadena, who was not involved in the study. "It creates the conditions for how we can prepare for the analysis of the ice by Europa Clipper," says the scientist.
Source: University of Texas at Austin, professional article: Astrobiology, doi: 10.1089/ast.2021.0044