Scientific Colloquium
January 7, 2005
The Mars Exploration Rovers Spirit
and Opportunity have both
found evidence for water-related
processes at their landing
sites. In Gusev crater, Spirit
found only trace evidence for
the action of water on the
lava-covered plains of the
crater floor. This water action
left thin salt-rich deposits
on the surfaces of rocks and in
fractures within rocks, and
what appear to be magnesium
sulfate salt concentrations in
soils. The older rocks in the
Columbia Hills, however, show
evidence for much more substantial
alteration by water. At
Meridiani Planum, Opportunity has
found layered sedimentary
rocks that we interpret to be a
mixture of fine-grained
silicate particles and chemical
sediments precipitated from
liquid water. Environmental
conditions that they record
include episodic inundation by
shallow surface water, evaporation
and desiccation. After deposition,
these rocks underwent a
complex history of modification by
water that resulted in
recrystallization and growth of
hematite-rich concretions.
A stratigraphic section obtained
within Endurance crater shows
significant variation of rock
chemistry and texture as a
function of depth. Environmental
conditions at Meridiani were
capable of supporting life at some
point in the planet's
history.