A "WATER STAIN" covers part of Meridiani Planum: a layer rich in
the iron-oxide mineral hematite. Discovered by the Thermal Emission
Spectrometer (TES) on the Mars Global Surveyor orbiter, the hematite -
which requires liquid water to form - led NASA to choose Meridiani as
the landing site for the Mars Exploration Rover Opportunity. Colors map
percentages of hematite in the surface materials. Opportunity landed within the black oval line and
found rocks that had once been drenched in water. Click on the image to
download a high-resolution version (5.8 MB). NASA/JPL/Arizona State
Christensen, P.R., and S.W. Ruff, The formation of the hematite-bearing unit in Meridiani Planum: Evidence for deposition in standing water, J. Geophys. Res., 109, E08003, doi:10.1029/2003JE002233, 2004.
Christensen, P.R., S.W. Ruff, R.L. Fergason, T.D. Glotch, N. Gorelick,
B.M. Jakosky, M.D. Lane, A.S. McEwen, H.Y. McSween, Jr., G.L. Mehall,
K. Milam, J.E. Moersch, S.M. Pelkey, A.D. Rogers, and W.B. Wyatt, Mars
Exploration Rover candidate landing sites as viewed by THEMIS, Icarus, 187, 12-43, 2005.