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Paper text:
space exploration is a difficult task and the search for life is no different .
the equipement size a probe can bring severely limit the scope of the search .
every sample can not be analyzed and selecting those that can be is not trivial .
this project investigates the possibilities of remote detection using infrared spectroscopy in order to select those few samples to pick and analyse further .
the reason for using ir spectroscopy is mainly that almost all biological marker molecules ( i.e. biomarkers ) will show some spectral features in the near to far ir ( @xcite ) .
furthermore , the spectroscopy will not destroy the sample ( e.g. there is no contact with the sample , no contamination ) .
previous techniques of detection tended to destroy , or damage , the endolithes or the environment in which they lived ( e.g. by using electron - microscope , chemical and biological or analysis ) .
biomarkers are an important source of information in the search for evidence of life in geological samples .
even if the organisms are dead or dormant , it is still possible to detect their presence , byproducts or even their chemical alterations of the environment .    in searching for extraterrestrial life ,
it is important to have a minimum of preconception about them in order to find it .
endolithes are organisms that live inside rocks or in the pores between mineral grains
. there are thousands of known species of endolithes , including members from bacteria , archaea , and fungi .
they represent near half the earth s biomass and also present an ideal model of life for mars ( @xcite , @xcite ) .
this study used two groups of samples .
one from the guelph region ( west of toronto , ontario ) and the other near eureka on the ellesmere island in the nunavut ( @xcite ) .
both regions have different geology and climate .
samples were scanned using a technique called diffuse scattering .
the ir beam was directed toward the sample and a series of mirrors redirected the scattered beam to the ir sensor .
the spectra were obtained using an ir nicolet spectrometer .
the apparatus used to collect the scattered ir beam could not receive large rock samples .
it was necessary to break them into smaller pieces .
the same device was very sensible to the angle of incidence and reflectance .
it was important to position both mirrors near the vertical above the sample .
the adjustment of each mirrors , in order to optimize the reception of light , was very time consuming .
those adjustments were performed using an aluminum plate as the sample to maximize the received flux to the sensor . when the rock sample was placed in the light path , the total flux drops a lot but the signal - to - noise ratio was high enough .
spectra in middle ir ( 132 ) and near ir ( 49 ) on 15 samples from the two groups were taken .
the best results were from the middle ir .
most of the spectra were taken at a resolution of 4 or 8 @xmath0 .
after analysis , it appears that a spectral resolution of 8 @xmath0 is enough for our purpose .
the middle ir spectra ( from 4000 to 650 @xmath0 ) were then processed using principal component analysis in order to classify them .
principal component analysis ( @xcite ) is a technique of factorial analysis ( e.g. multivariate statistics ) .
it is often used to find a new coordinate system in which the original data will be better aligned on some axes ( e.g. principal components ) .
the technique can be summarized by the equation @xmath1 where a , u , w and v are matrices .    _
a _ is a @xmath2 matrix containing the spectra on each row .
the value of each absorption band is then regrouped in the columns which are the variables on which the pca works .
_ u _ , also a @xmath2 matrix , contains the spectra in the new coordinate system .
the matrix _ v _ , where @xmath3 is an identity matrix , contains the eigenvectors .
_ w _ is a diagonal matrix containing the squared root of the eigenvalues and provides a clue about how many principal components ( pc ) can be used to describe the data .
it is important to have a matrix _ a _ with more columns than rows ( ie .
@xmath4 ) else _ w _ becomes a singular matrix and the whole pca fails .    to facilitate data manipulation and visualization for this paper , we have taken only the first three principal components .
the result of the pca process is illustrated in figure 1 .
the process can be extended to as many components as needed .
based on the eigenvalues from our data , the first five components are relevant , the others being buried in the noise .
we have identified several clusters . cluster _
e _ groups the spectra containing features showing the presence of organic compounds . cluster _
is very close to another cluster of points calculated from organic spectra used as a reference ( i.e. cluster o ) .
further , most of the spectra of cluster _ e _ have been taken directly from green regions visible on the samples .
our results show that it is possible to detect biological signatures using a spectrometer operating in the middle infrared range . however , it is not possible to highlight a particular region , or regions , in a spectrum to be used to identify biomarkers .
the interdependance of the absorption bands related to the living are too complex to simply isolate a few .
the proposed technique calls for a more subtle approach by comparing witness spectra and an unknown spectrum by plotting them in the pca s space .
if the test spectrum , once projected into the pca s space , is close to the reference group then the probability of it is containing biomarkers is high . adding a non - organic spectra to the pca space as references may improve the idenfitication scheme
this technique could be used to pinpoint potential life harboring rock for more detailed analysis .
it could be possible to extend the method to better idenfity the unknown spectrum using a more precise reference database .
hand , k.p . ,
carlson , r.w . ,
sun , h . , anderson , m , wadsworth , w. , levy , r. , 2005 , utilizing active mid - infrared microspectrometry for in - situ analysis of cryptoendolithic microbial communities of battleship promontory , dry valleys , antartica , astrobiology and planetary missions , vol 5906 , p.302
on earth , the dry valleys of antarctica provide the closest martian - like environment for the study of extremophiles . 
 colonies of bacteries are protected from the freezing temperatures , the drought and uv light . 
 they represent almost half of the biomass of those regions . due to 
 there resilience , endolithes are one possible model of martian biota .    
 we propose to use infrared spectroscopy to remotely detect those colonies even if there is no obvious sign of their presence . 
 this remote sensing approach reduces the risk of contamination or damage to the samples .