EXTREME BLADED ROUGHNESS ON THE SURFACE OF EUROPA AT THE LANDER SCALE

The surface roughness of Europa on the meter scale is a vital parameter to understand if we wish to deliver a lander to this moon in the future. However, direct imaging of the surface is of too coarse a resolution to resolve features on this scale, and traditional photometric analyses of electromagnetic waves reflected or emitted from the surface have not sought to distinguish lander-scale surface roughness from finer and coarser scales. This is problematic, since degrading ice on Earth forced by solar radiation is known to develop significant surface roughness on the 10^-1 - 10¹ m scales in the form of suncups, penitentes, and dirt cones, and it not unreasonable to assume that the icy surface of Europa might develop roughness on similar scales in the face of long timescale exposure to solar flux.

We demonstrate from that given Europa’s known surface conditions, it is expected that the extreme bladed roughness elements known on Earth as penitentes will be present in a wide band around the planet’s equator. Furthermore, the presence of such features here would explain problematic observations of that moon’s equatorial thermal inertia, and may contribute to Europa’s uniquely strong and sharp “opposition effect” in its photometry. We go on to quantify how 30-year-old unexplained radar observations that Europa has a positive circular polarization ratio can also be explained by these same features. This last observation also suggests that other Galilean moons may also exhibit this same surface texture.