Columns of compact snow called Nieve penitente with moon

Icy spikes called penitentes — seen here in Chile — might also form on Jupiter’s moon Europa. Credit: Art Wolfe/Getty

Planetary science

Spacecraft beware: huge spines of ice might guard a glimmering moon

Touchdowns on Jupiter’s moon Europa, which might host life, could be risky.

The Jovian moon Europa might bristle with 15-metre-tall ice blades around its equator, posing a formidable hazard for future missions to the surface.

Images of Europa, which probably harbours a saltwater ocean, have led scientists to think that a lander could touch down on the moon’s icy, seemingly smooth surface. But a team led by Daniel Hobley at Cardiff University, UK, suspected that the surface ice could sublimate, or change from a solid to a gas without melting, to form spine-like structures called penitentes.

These spikes form on Earth when a steady stream of sunlight repeatedly reflects back and forth inside small pits in cold, dry snow. The sunlight’s heat causes snow from the pits’ edges and bottoms to sublimate. The pits grow wider and deeper until only their edges remain, as tall blades of ice.

The team used surface temperature and reflectivity data to estimate sublimation rates across Europa. The results suggest that conditions at Europa’s equator could spur the formation of massive penitentes spaced 7.5 metres apart.