13 May 2004

Speaker: Philip Christensen (Arizona State University)

Title: The history of water on Mars: Evidence from minerals, morphology (and rovers).

Abstract: A wealth of recent orbital and surface measurements of the mineralogy, elemental abundance, and morphology of the martian surface have greatly improved our view of the history of water on Mars.Mineralogic data from orbital spectroscopy reveal a dry, volcanic planet that lacks extensive aqueous weathering or carbonate formation.However, there are local regions, such as the remarkable example of the Opportunity Rover landing site, where orbital and in situ observations suggest a lake once existed that produced significant localized aqueous mineralization.Mid- to high-latitude hydrogen abundances and unusual morphologies suggest that there are extensive accumulations of near-surface water ice that can melt during climate oscillations to form modern gullies. Overall, the upper surface of Mars appears to have an extensive water inventory, but this water may have existed in a frozen state throughout much of martian history.Can these disparate views of a "dry Mars",, a "wet Mars, and an "icy Mars" be reconciled into a coherent picture of the evolution of the climate and the state of water on this planet?

Video of the Presentation (Talks can be viewed with RealPlayer. Free download is available from www.real.com )

References for students:

1. Christensen, P.R., Formation of recent martian gullies through melting of extensive water-rich snow deposits, Nature, 422, 45-48, 2003
2. Christensen, P.R., et al., Morphology and composition of the surface of Mars:Mars Odyssey THEMIS results, Science,300, 2056-2061, 2003
3. Malin, M.C., and K.S. Edgett, Evidence for persistent flow and aqueous sedimentation on early Mars, Science, 302, 1931-1934, 2003
4. Christensen, P.R., M.C. Malin, R.V. Morris, J.L. Bandfield, and M.D. Lane, Martian hematite mineral deposits: Remnants of water-driven processes on early Mars, J. Geophys. Res., 106, 23,873-23,885, 2001.