Detection of Biosignatures in a Mars-Like Environment Using LIBS

Details Detection of Biosignatures in a Mars-Like Environment Using LIBS Detection of Biosignatures in a Mars-Like Environment Using LIBS

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p43c1452o&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P43C-1452

Physics

[5494] Planetary Sciences: Solid Surface Planets / Instruments And Techniques, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Mars Science Laboratory (MSL), due to launch in Feb 2011, will continue the exploration of the Martian surface with a focus on the search for habitable environments. Organic carbon detection is of key interest. The LIBS (Laser-Induced Breakdown Spectroscopy) instrument, part of the on-board ChemCam suite, is capable of detecting elemental components (e.g. C, N) of organic molecules as well as C2 and CN species. LIBS is likely to be the one of the most productive analytical tools of MSL due to its rapid analysis rate, low power requirements, and its ability to interrogate target materials at stand-off distances of up to 7 m from the rover. Its usefulness will depend, in part, on the science team’s ability to correlate Martian data with a suite of well-characterized spectral reference materials. Here, we present preliminary results of LIBS analyses of organic-mineral mixtures conducted in a Mars-like atmosphere. LIBS works by focusing a pulsed laser beam on the target and ablating a sub-millimeter sized spot, producing a plasma of electronically excited ions, atoms, and small molecules which emit light at characteristic wavelengths as they relax to lower electronic states. Targets, comprised of a series of pressed pellets with variable amounts (0-100 wt. %) of the amino acid cystine (in dimer form) and kaolinite, were heated to remove adsorbed water prior to weighing and mixing. During analysis, they were contained in a chamber with an atmosphere similar to ambient Mars (~9 mbar CO2). LIBS analyses were conducted in situ using a pulsed (10 Hz) Q-switched 1064 nm Nd:YAG laser at 17 mJ per pulse. Each measurement (0.5 μs delay, 1 second exposure, 150 detector gain) was obtained by collecting 10 shots per second per spot, averaging 3-5 spots per sample. Each spectral channel intensity value was normalized to the total emission of that spectrum, to eliminate the effect of slight variations in laser pulse energy. The plasma light was transmitted to a Catalina Scientific echelle spectrograph with a spectral range of 200-1000 nm and a spectral resolution of 0.02 nm. Emission bands due to CN (at 387.14 nm and 388.34 nm) had the highest intensity; C, H, and O emission lines were also prominent. C2 ‘Swan’ bands were not detected. Peak areas for the C emission (247.856 nm) in all 5 samples were determined and plotted against mol% C to calibrate the variation in concentration and emission line intensity. Our preliminary results reveal a direct correlation between peak area and the amount of carbon in a sample. Emission lines were readily detectable in our sample with the lowest C content (~ 7 mol%); further work is needed to determine threshold C detection limits with our current as well as stand-off configurations. We are applying statistical analysis to improve our quantitative results and correct for matrix effects in samples of different composition.

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