First of all, the 1976 Viking lander did NOT find organics on Mars. This is not just because the mass-spectrometer they flew was 3 orders of magnitude too insensitive to find organics from either the Atacama desert or the dry valleys of Antarctica, but also because sulfur poisoned the palladium foil that was intended to concentrate the organics for analysis.
The labelled-release experiment of Gil Levin, however, did find evidence of bacterial metabolism. You can read the papers on his website: http://mars.spherix.com/mars.html. It was tested against soils in Antarctica and Atacama, and in both cases found microbes unlike Carl Sagan's mass spectrometer. Carl ran interference and made sure Gil's work didn't get published, but I've told that story elsewhere.
But being a mass spectrometer, and being designed for low-molecular weight gases, Sagan did NOT find perchlorates in the soil either. They would have seen them had they been there. They would have seen the chlorine too--it has an unmistakeable signature. And it would sorta have explained Levin's data because the perchlorate would have oxidized the organics to produce CO2. But they didn't see it. Nothing. Nada, despite there being good explanation if it had existed.
So Carl Sagan argued for super-metallo-peroxides. Why? Because they would produce hydrogen peroxide when water was added, which presumably would evolve carbon dioxide as measured in Gil Levin's experiment without leaving a telltale signature in the mass spec. This theory persisted despite not finding any hydrogen peroxide in the atmosphere which the chemistry required.
So once again. The results of Viking were no organics due to insensitivity and poisoning, and certainly no perchlorates.
Fast forward 32 years to 2008, and we have the Phoenix lander that decided NOT to use mass spectroscopy, but wet chemistry to determine the makeup of Mars soil. In my mind, I can't find a single reason why this is a better measurement. It's less sensitive, less accurate, less general, less power-efficient, less lightweight, less robust, etc. But nothing in the Mars program makes sense without understanding the politics, so I just assume there was someone who had the ear of a congressman. Well, in order to prep the spacecraft for detecting organics, they had to remove finger prints (or as my mechanical engineer used to say, fried chicken grease) from the satellite. How did they do this? Why, with a perchlorate wash of course.
Do you suppose...Nah, the team reported, it couldn't possibly be contamination. Why, it agreed with the Viking results!
