There are two new MER-related papers in the December 22, 2005, issue of Nature. See also the the accompanying News and Views piece by Mark Bullock.

Mars Region Probably Less Watery In Past Than Thought, Says Study
December 21, 2005
University of Colorado at Boulder News Services

I was interested in how McCollom and Hynek would account for jarosite in their model, so I noted the following excerpt (with internal references omitted) from their paper:

"Jarosite, a mineral observed in the Meridiani bedrocks, did not occur in any of our equilibrium models. Because jarosite is unstable in equilibrium with haematite, it apparently persists as a metastable mineral owing to kinetic constraints and may have formed during evaporation or as a weathering product subsequent to other alteration."

In addition, Figure 1 from their paper is a ternary diagram that shows the Meridiani bedrocks falling on a mixing line between martian basalts and the pure sulfur endmember.

Interesting.