Where Underwater Snow Exists On Earth
31 December 2022
It appears that conditions beneath Europa’s ice shell are similar to those on Earth’s ice shelves, which occasionally experience the strange phenomenon known as underwater snow. Polar ice shelves replenish themselves through two processes, one of which is the extraordinary phenomenon occasionally referred to as underwater snow. It is believed that Europa’s icy exterior and likely other worlds with interior oceans go through something similar. A better understanding could assist the Europa Clipper’s operators in knowing what to look for in terms of life-supporting conditions before the ship is launched in 2024.
There has been life on Earth for the majority of its history, but not a lot of it has been on land. As a result, worlds like Europa and Enceladus with their oceans beneath icy shells may offer better chances of discovering extraterrestrial life than dry Mars. Natalie Wolfenbarger, a graduate student at the University of Texas at Austin, is using oceanic ice shelves as analogues for outer solar system moons, much like astrobiologists go on expeditions to the Atacama Desert and dry regions of Northern Canada to find the closest Martian proxies.
In Astrobiology, Wolfenbarger and co-authors discuss the characteristics of these shelves and how they affect the water below them. They contend that these shelves are more important than the more well-known but thinner sea ice. As they note, “Much attention has been directed towards the uppermost layer of the ice shell because existing observations [of ice-covered ocean worlds] are mostly confined to the surface.” The underside, however, has probably been overlooked because it is more significant. In a statement, Wolfenbarger said, “We’re interested in the salinity and composition of the ocean when we’re exploring Europa because that’s one of the things that will govern its potential habitability or even the type of life that might live there.
If we’re making the wrong assumptions about how the ice forms, current extrapolations from ice to ocean composition may be flawed. According to the paper, the shelves are made of frazil ice and congelation ice, which is hopefully the cooler version of Fraggle Rock. Congelation ice is known to contain significantly less salt than the ocean below and is created when water in contact with an existing shelf freeze. However, it turns out that frazil ice, which is more poetically referred to as underwater snow, is even purer. Frazil ice blocks out about 99.9 per cent of the salt, according to the paper, whereas congelation ice has about 90 per cent less salt per litre than the ocean, rising to 99 per cent under certain conditions.