QUESTION:
I saw one picture taken by the rover on a CNN broadcast of what appeared to
be ripple features suggestive of fluvial activity.  The ripples appeared to
be in the uncemented regolith. Is this the case? If so, what are the
implications for the age of the feature? I understand that there is no
suggestion that the outflow channel feature in which the probe has landed
has been active for millions of years. If this is the case, how likely is it
that soft sediment features will be preserved at the surface given the
erosive effect of the Martian winds?

Additionally, in a more general sense, it appears that there is a general
consensus is that there has been no fluvial channelling activity on the
surface in the recent geological past.  What is the Pathfinder Team's view
of the likliehood of groundwater seeps continuing at the present time in
geologically active areas such as around Valles Marinaris? Is shallow
subsurface flow possible due to increased overburden pressures providing the
required PT conditions and if so, could the seepage channelling features so
common around the canyon edges still be active?

ANSWER from Mary Urquhart on August 26, 1997:
Large ripple features (undulations on the order of meters in size) do appear
to be present at the Pathfinder landing site providing even more evidence
that the area was experienced catastropic flooding.  The actual time since
the flooding occurred is probably 1 to 2 billion years based on the impact
craters visible in the Viking orbiter images.  There is unconsolidated
material at the landing site clearly visible on rocks and by the tracks of
Sojourner, but the depth of unconsolidated sediment really isn't known.  In
order to consolidate the sediment some cementing material such as salt or
ice must be present.

However, if the ripples are composed entirely of unconsolidated sediment,
that isn't a problem considering the very slow rate of erosion from just
wind (see my answer on wind and water erosion rates in the LFM question
database).  If you are refering to the small scale ripple features seen near
some of the rocks for instance, those are probably wind rather than water
features.

For your second question, I'm not on the Pathfinder Team, but I'll give you
my answer anyway.  Valles Marineris opened in a time period known as the
Early Hesperian (3.5 billion years ago give or take 400 million years or so)
and was probably due to tectonism (faulting and fracturing of the crust of
Mars) maybe as a result of the formation of the Tharsis bulge.  The canyon
system of Valles Marineris is really more of a system of troughs (the term
canyon can imply formation by water which is in this case incorrect).

The slopes of the walls of the Valles Marineris system are very steep
despite their depth in some places of 8 to 10 km below the plateau.  The
stability of these slopes over extremely long periods of time suggests that
they contain very little water or ice.  The great height of the walls also
argues against any volcanic or water activity which would have caused rapid
infilling of depressions.  The tributary canyons that are apparently formed
by sapping of groundwater are of questionable age.  However, some
researchers have argued that they appear to be immature suggesting that the
aquafers providing the water may have dried up arresting the formation of
the sapping valleys.  In any case, it is highly unlikely that sapping (or
water seepage) features are presently forming in Valles Marineris.

Mary Urquhart                                    
Laboratory for Atmospheric and Space Physics  
University of Colorado at Boulder