I thought it was well known that the surface of Mars is very oxidised. All that Fe2O3 making the place red.

The Labelled Release experiment carried by the Viking landers, in which the soil had some nutrient solution added to try and get any "life" to metabolise and give off gases, resulted in the surprising vigorous release of CO2. http://en.wikipedia.org/wiki/Viking_...al_experiments The simplest inorganic explanation for this is that the soil contained a vigorous oxidising agent. So when I heard they had found perchlorate, I wasn't in the least surprised. But I'm simplifying, I think it is more controversial than that.