Geoscience Reference
In-Depth Information
(a)
(d)
(b)
(c)
Figure 5.1
Arid landscapes of four worlds: (a) Earth (Atacama desert); (b) Mars (Columbia Hills, Gusev Crater); (c) Venus (Phoebe
Regio); (d) Titan (Xanadu Regio). Image (b) NASA; (c), original
Venera
data reprocessed by Don Mitchell (used by permission);
(d), NASA/ESA.
surface temperatures well below the range of liquid water,
have a wide range of landforms that on Earth would be
considered typical of humid (apparently permanent lakes
and streams, Mitri
et al.
, 2007) and arid (large-scale lon-
gitudinal dune fields, Lorenz
et al.
, 2006)?
To allow for these observations it is proposed that on a
planetary scale 'arid geomorphology' should be expanded
to include those bodies with a solid surface and with an
atmosphere sufficiently dense to allow any liquid phase
to condense and play a role analogous to water in some
way. These definitions both exclude the gas giants such
as Jupiter and airless bodies like the Moon. This defini-
tion includes Venus and Titan as bodies that are partly
to completely arid with very different condensable atmo-
spheric liquids (sulfides on Venus and methane on Titan).
At present it also excludes bodies such as Triton, where
the atmosphere modifies the surface (Greeley, 1994) but
is too attenuated to allow the condensation of a liquid
phase.
5.3
Why should planetary scientists
understand terrestrial arid geomorphology?
Our ability to study the surfaces of other bodies in the so-
lar system is still severely limited in many respects. Plan-
etary geomorphologists must rely heavily on terrestrial
analogues for the features they observe, with all the limi-
tations this entails. This requires a high level of familiarity
with terrestrial surface processes across a wide range of
environments and regions. There is an unfortunate reliance
on a comparatively small number of analogues from the
southwest of the United States; this should be expanded
