Good summaries and reviews of the results of the MER rover Mars missions.

Mostly about the Spirit mission at Gusev crater:

Remote Sensing Tutorial Page 19-13a
Missions to Mars during the Third Millenium
http://rst.gsfc.nasa.gov/Sect19/Sect19_13a.html

and:

Remote Sensing Tutorial Page 19-13b
http://rst.gsfc.nasa.gov/Sect19/Sect19_13b.html

which is mostly about the Opportunity mission at Meridiani.

This second also has a link to a report that might offer an
explanation for the lack of carbonates at the Meridiani landing site:

ACID SEDIMENTARY ENVIRONMENTS ON MARS?: POSSIBLE TERRESTRIAL ANALOGS
http://gsa.confex.com/gsa/2002AM/fin...ract_36936.htm



Bob Clark