Other Dune Worlds - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 171

several nanobar. This large discrepancy can be sustained
because the gas can condense out onto the surface before it
is transported around the moon. The discrepancy suggests
some uneven supply of gas—perhaps a greater supply from
volcanic plumes, which are also more abundant on the
antiJovian hemisphere, or perhaps more abundant or war-
mer frost deposits. This spatial variability might similarly
imply that temporal variability can occur too.
Aeolian transport in such a tenuous atmosphere seems
unlikely. However, the 'atmosphere' in the immediate
vicinity of volcanic plumes might be substantially thicker,
and while particle transport here may severely stretch the
definition of 'aeolian', it cannot be ruled out entirely and is
instructive to consider.

Figure 15.2 shows sulphur dioxide frost that appears to
have jetted horizontally (perhaps from a frost deposit
overrun by silicate lava) that highlights the rippled texture
of the ground. This rippled texture may simply be tectonic,
but the possibility of aeolian deposits cannot be ruled out.
The ridge spacing is 100-200 m: it seems possible to
contrive scenarios (using the drag length or saltation path
arguments discussed in Chaps. 4 and 5 ) wherein such
wavelengths are consistent with particle movement in a thin
atmosphere.
Future missions to Io are being considered in NASA's
planning, although would not arrive until the mid 2020s at
the earliest. We may hope that such missions have the
capability to explore these features in more detail.