Posted: August 6, 2008
Phoenix mission scientists are currently investigating perchlorate salts detected in soil analysed by the wet chemistry laboratory, but the jury is still out as to the importance of the discovery for life on Mars.
Perchlorate consists of an atom of chlorine surrounded by four oxygen atoms, and was discovered in two separate samples by the MECA (Microscopy, Electrochemistry and Conductivity Analyser) suite of instruments, which includes the wet chemistry lab that studies soluble chemicals in soil samples by mixing the soil with a water-based solution. Perchlorate is also an oxidant, which means it can release oxygen, albeit rather weakly, and it plays an important role in fueling some microorganisms on Earth, as well as occurring naturally in arid desert conditions.
"Finding perchlorates is neither good nor bad for life, but it
Two samples were delivered to the wet chemistry lab on 25 June and 6 July, and showed evidence for perchlorate salts. The first sample was taken from the surface area just left of the trench and the second sample from the centre of the Snow White trench. Image: NASA/JPL-Caltech/University of Arizona/Texas A&M University.
The Phoenix team have taken an unusual step in reporting on these results half way through the investigation, following claims in the press that a major finding regarding habitability on Mars was being held back.
"We are committed to following a rigorous scientific process. While we have not completed our process on these soil samples, we have very interesting intermediate results," says Peter Smith, Phoenix principal investigator. "We decided to show the public science in action because of the extreme interest in the Phoenix mission, which is searching for a habitable environment on the northern plains of Mars. Initial MECA analyses suggested Earth-like soil. Further analysis has revealed un-Earthlike aspects of the soil chemistry."
The scientists are still at the stage where they are examining multiple hypotheses resulting from the wet chemistry experiments and the TEGA analysis, which detected a release of oxygen, but no sign of chlorine. According to the mission chemists, perchlorate could be one of several possible sources of this oxygen.
"Had we seen it [chlorine], the identification of perchlorate would be absolutely clear, but in this run we did not see any chlorine gas,” says TEGA lead scientist William Boynton. “We may have been analysing a perchlorate salt that doesn't release chlorine gas upon heating, but there's nothing in the TEGA data that contradicts MECA's finding of perchlorates."
As the Phoenix team continues its investigation of the arctic soil, the TEGA instrument will attempt to validate the perchlorate discovery and determine its concentration and properties, as well as totally exonerate any possible terrestrial contamination.
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