So, you are a geoscientist and you are interested in Mars.  Excellent!  Now read pages 793 to 845 of the 6 August 2004 issue of Science v. 305.  There is much to learn from 11 papers about the less revealing of the two Mars Exploration Rovers, Spirit.  Rover Opportunity has been getting the headlines, with its discoveries that relate to the influence of surface and subsurface water on superficial Martian minerals, such as the now well-publicised “blueberries” made of hematite, and the presence of sulphates.  A more informative digest of the mineralogy of Mars appears in the same issues’ News Focus (Kerr, R.A.  2004, Rainbow of Martian minerals paints picture of degradation.  Science, v. 305, p. 770-771).  Kerr makes clear that the really revolutionising instrument is orbiting Mars; the Visible and Infrared Mineralogical Mapping Spectrometer or OMEGA.  That is part of the payload of the ESA Mars Express, and measures radiant energy from the Martian surface with such spectral and spatial resolution, that the results can be compared with standard spectra of terrestrial minerals to see what the Martian surface is made of.  Hopefully, OMEGA will produce a hyperspectral database for the entire planet.  The on-surface readings from the various instruments on the NASA Rovers play much the same role as a field geologist would, by providing “ground truth” to validate the broader scope of the OMEGA instrument.  The hematite that dominates the overall red colour of Mars, has been confirmed by the Rovers, but to nobody’s great surprise.  The exciting find is just how much is owed to sulphate minerals, such as orange iron potassium sulphate, or jarosite.  The sulphate-rich veneer could well point to the influence of sulphuric acid, let alone water in Mars’ early surface environment, probably emitted as sulphur dioxide during intense volcanic activity.  Interestingly, the incompatibility of highly acid surface water with the preservation of carbonates could have thwarted drawdown of CO₂ from the Martian atmosphere (Fairén, A.G. et al. 2004.  Inhibition of carbonate synthesis in acidic oceasn on early Mars. Nature, v. 431, p. 423-426).  Formation and preservation of soil carbonate minerals would have collapsed the “greenhouse” warming mechanism demanded by the now proven influence of flowing water early in Martian history.  So long as sulphurous volcanic emissions overwhelmed carbonate formation, Mars might have stayed wet and warm.  The key is the duration of massive volcanism, which could be tied down by seeing how lavas have been affected by impacts in the minute detail possible from another Mars Express imaging instrument, the High Resolution Stereo Camera.  Planetary volcanic specialists reckon massive volcanism lasted for a considerable time