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