Other Dune Worlds - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 169

Fig. 15.1 Voyager 2 image of
the surface of Triton. Many dark
streaks can be seen, all pointing
at around 5-o'clock, suggesting
transport by a regional wind
pattern. The extent to which the
material merely drifts downwind
while settling out from a vertical
plume, versus being transported
by saltation along the surface, is
not known. Image NASA

pressure substantially, and only a small change in heat flux
can change the surface temperature). The changes are likely
caused by the elliptical orbit of Neptune around the sun, and
thus

than being saltated along the ground and forming dunes or
ripples. There is, however, no observational evidence for or
against the existence of bedforms.
While no near-term exploration of Triton is expected the
New Horizons spacecraft, launched in 2006, is set to fly past
Pluto and its moon Charon in 2015. Pluto may in some
respects resemble Triton, although the best imaging reso-
lution of Pluto will likely be of the order of 50 m/pixel, so
dunes—if present at all—would have to be large to be
detectable. On the other hand, the saturation length in a thin
atmosphere, and thus the expected bedform length scale, is
large. Another moon, Io, offers a tentative example.

further change (unobserved at present) has likely

occurred.
Groundbased spectroscopy (Grundy et al. 2002) suggests
that nonvolatile materials are widely distributed on Triton:
the fact that such materials are evident even though subli-
mation and condensation of nitrogen and methane should
seasonally deposit 'clean' frosts may imply that winds can
redistribute finely-grained material quite quickly. The
material should not be produced fast enough by photo-
chemical processes to be detectable in seasonal frosts

(Fig. 15.1 ).
The particles appear to derive from point sources, likely
associated with eruptive plumes (e.g., Hansen et al. 1990;
these probably solar-driven plumes have been sometimes
referred to, almost certainly incorrectly, as 'geysers') in
which case the streaks are more likely just the downwind
fallout of dust blasted into the sky by the plumes, rather

15.2 Io

Jupiter's innermost large moon, Io, has a constitution rather
similar to the terrestrial planets, with iron, sulphur and sil-
icates. It is in an orbital resonance with Europa and Gan-
ymede, that maintains a substantial eccentricity to its orbit