Blades of metres-tall ice may cover the equatorial regions of Europa, Jupiter’s frozen moon, reports a study published online this week in Nature Geoscience. Such jagged terrains would pose a hazard to any future space mission landing on the moon.

Europa’s subsurface ocean makes it a promising target in the search for extraterrestrial life. However, it is unclear how easy it would be to safely land a spacecraft on this icy moon. Europa’s surface is fragmented by grooves and ridges and we lack sufficiently high-resolution imagery to determine how smooth the ice is between these features. In extreme cold and dry conditions on Earth, such as those encountered in the Andes, the Sun’s rays can cause parts of the ice and snow to undergo sublimation - becoming water vapour without melting first - leaving behind distinctive, blade-like formations called ‘penitentes’. Evidence of penitentes has also been seen on Pluto, suggesting that such jagged terrains may be common on icy worlds - including Europa.

Daniel Hobley and colleagues calculated the sublimation rates of water ice across Europa’s surface and compared these to the other erosional processes - such as impact events and charged particle bombardment - that act on the moon’s surface. Sublimation would produce rougher surfaces, whereas the other processes would have a smoothing effect. The authors find that, in equatorial regions, sublimation should be the main erosional process, and is sufficient to sculpt penitentes. Over time, they suggest, penitentes of up to 15 metres tall spaced about 7 metres apart could form - creating a treacherous terrain that will need to be considered when planning future missions to Europa.