Ever since the NASA Viking mission, which reached Mars in 1976, there has been considerable interest in the composition of Martian soils. Some Viking measurements indirectly suggested that the soils contained highly oxidizing compounds, which could present extremely harsh conditions for life. Recent observations from the Phoenix Mars Mission pointed to evidence of perchlorate, a potentially highly oxidizing compound, in the Martian soils. However, some studies have noted that because perchlorate is highly stable, its presence in Martian soils cannot explain the Viking measurements.
Quinn et al. present a new analysis of Mars soil samples using the Wet Chemistry Laboratory, a component of the Microscopy, Electrochemistry, and Conductivity Analyzer on the NASA Mars Phoenix Lander. They find that although low levels of oxidizing compounds may be present, the oxidation-reduction potential of the soil is moderate and well within the range expected for habitable soils.
Source: Geophysical Research Letters, doi:10.1029/2011GL047671, 2011
Title: The oxidation-reduction potential of aqueous soil solutions at the Mars Phoenix landing site
Authors: Richard C. Quinn: Carl Sagan Center, SETI Institute, NASA Ames Research Center, Moffett Field, California, USA; Julie D. Chittenden: Postdoctoral Program, NASA Ames Research Center, Moffett Field, California, USA; Samuel P. Kounaves: Department of Chemistry, Tufts University, Medford, Massachusetts, USA; Michael H. Hecht: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA.