Predicting the surface of Europa

Equatorial regions of the potentially life-supporting Europa, which harbors a huge ocean of salty liquid water beneath its icy shell, are probably studded with blades of ice up to 50 feet (15 meters) tall, a new study suggests.

Here on Earth, exceptionally cold and dry conditions, such as those found in the Chilean Andes, can give rise to rows of jagged ice towers called "penitentes" (Spanish for "penitent," so named because they often look like people kneeling in penance). The driving force behind penitente formation is sublimation, the transition of a material directly from solid to gas form. An initially smooth snowpack sublimates at different rates in different spots, causing small pits to form in some places. Sunlight bounces around in these pits, boosting sublimation further in the depths and eventually creating fields of spiky ice towers.

So Hobley and his colleagues calculated sublimation rates around the surface of the Jupiter moon and then compared those with the rates of other erosional processes. The researchers found sublimation to be the dominant factor on equatorial Europa, the regions within 23 degrees of the moon's equator. And sublimation has likely carved penitentes into the ice there, the study team determined. These are some serious putative penitentes, too: Some fields could feature towers up to 50 feet (15 m) tall, spaced about 23 feet (7 m) apart, the scientists found. Here on Earth, penitente heights typically range from 3 to 16 feet (1 to 5 m).

There's some observational support for the existence of Europa penitentes as well, the researchers reported. For example, radar waves beamed at Europa from big Earth-based dishes such as Puerto Rico's Arecibo Observatory show signs of bouncing off multiple surfaces on the moon — a result that Hobley described as "really weird."

https://www.space.com/42051-jupiter-moon-europa-ice-towers-lander.html