Proceedings Article | 14 September 2006
KEYWORDS: Principal component analysis, Mars, Carbon, Statistical analysis, Stochastic processes, Scanning electron microscopy, Artificial neural networks, Chlorine, Sodium, Aluminum
Analysis of spectral and imaging data from meteoritic samples and sample return missions would benefit
significantly from a systematic, quantitative statistical classification methodology and a common set of standards for
data collection [McDonald and Storrie-Lombardi, 2006]. Stochastic artificial neural networks can be trained using
elemental abundance distributions for the detection of macroscopic fossils [Storrie-Lombardi and Hoover, 2004]
and extant microbial life [Storrie-Lombardi and Hoover, 2005]. These non-linear algorithms are particularly
attractive since they can produce a Bayesian estimate of the classification accuracy of either human experts or
automated, unsupervised classification algorithms. In sub-ocean and surface basalts on earth the networks can
distinguish regions of biotic and abiotic alteration of basalt glass from unaltered samples using only elemental
abundances as inputs [Storrie-Lombardi and Fisk, 2004b]. Recently, evidence has been presented documenting the
presence of morphologic signatures in the Mars meteorite Nakhla [Fisk et al., 2004; Fisk et al., 2006] previously
noted in regions of biotic alteration in sub-ocean and surface terrestrial basalts [Fisk et al., 2003; Furnes et al.,
2004]. The tunneling alterations are not conclusive evidence of biotic alteration of Nakhla on Mars. However, the
meteorite is well known to have experienced aqueous alteration prior to arrival on earth and is rich in carbon
[Gibson et al., 2006; McKay et al., 2006]. We here present an initial application of our probabilistic classification
strategy to assess elemental abundance distributions from multiple target regions in Nakhla and lunar dust samples
collected by Apollo 17 astronauts. We present scanning electron microscope images and elemental abundance point
distributions (C, N, O, Na2O, MgO, Al2O3, SiO2, P2O5, S, Cl, K2O, CaO, and FeO) for a series of target regions.
We discuss our observations in the context of data previously presented in these meetings for extant cyanobacteria,
fossil trilobites, Orgueil meteorite, and terrestrial basalt targets. These data are being added to a database that will
made available to the biogeology and astrobiology communities as part of an ongoing effort to provide a quantitative
probabilistic methodology for analysis of putative elemental abundance geobiological signatures.
