Io is Jupiter’s third-largest moon and the most volcanically active body in the solar system. The widespread volcanic activity occurs because Jupiter’s gravity pulls on Io, generating interior heat that drives eruptions onto the surface. In addition to a rugged volcanic landscape, Io’s icy surface has meandering features that are similar to dunes and ridges on Earth and Mars. A recent study published by George McDonald (Rutgers University) and colleagues shows that Io’s dune-like landscape likely results from the interaction between lava and frost.

Dunes are hills of sand piled up by aeolian (due to the action of wind) processes. However, Io’s low-density atmosphere results in weak winds, which suggests that these dunes are sculpted by some other airborne force. On Earth, similar forces occur when molten rock encounters water, producing powerful explosions of steam. Although water is not present on Io, McDonald and his team considered the pervasive occurrence of sulfur dioxide frost. They hypothesize that slow-moving lava underneath a layer of frost creates jets of vapor that are dense and fast enough to transport grains and form large dune-like features on the moon’s surface. This process is referred to as saltation. The team calculates that the jets are strong enough to mobilize grains between 20 micrometers to 1 centimeter in diameter and build dunes over 30 meters tall. Their work is supported by images taken by NASA’s Galileo mission, which reveal that the dimensions of Io’s dunes are consistent with those seen on Earth and other worlds.

Indeed, dune-like features have also been observed on comet 67P and Pluto, both of which lack thick atmospheres. The work by McDonald and his colleagues adds Io to a growing list of planetary bodies with weak atmospheres on which aeolian sediment transport may be an important control on landscape evolution. READ MORE