  Several measurements, including the data from the laser spectrometer in the
Sample Analysis at Mars instrument suite on the Curiosity Rover in Gale crater,
have measured seasonal variations in atmospheric methane at the 0.7 ppbv (parts
per billion volume) level. As a result, models have been proposed to understand
the methane production including novel chemical, geological, meteorological,
and biological mechanisms. Biological models often rely on methanogenic
extremophile archaea which might be similar to some Earth based organisms which
can be studied exhaustively in a laboratory setting. Such organisms might
thrive in a subsurface ecosystem involving water and methane and as such could
leave a unique biosignature in the Martian regolith that could be preserved
over extended periods of time. The resulting mixture of carboxyl, acetyl and
hydroxyl groups blended with the metallic sulfates and regolith constituents
could produce a Raman signature detectable on the next rover mission if the
concentration is high enough. Here we measure the 532 nm and the 780 nm Raman
spectra of a variety of molar concentrations of several hydrated metallic
sulfates mixed with JSC-1 Martian regolith simulant to identify the signature
concentration thresholds for the isolated C=O Raman peak from acetic acid. We
find a Raman peak removed from most fragmented molecular Raman bands near 1608
cm-1 using the 532 nm laser for the Fe and Mg sulfates to yield a threshold in
the 120 - 160 ppmv range for a cutoff S/N of 2.
