Exobiology in the Solar System & The Search for Life on Mars - ESA

Consideration of a diamond wire-saw or blade-saw should be <strong>in</strong>cluded <strong>in</strong> <strong>the</strong>
sample preparation scheme. A diamond wire-saw to cut rocks of about 1-5 cm
diameter would basically consist of two wheels (5 cm and 1 cm diameters), a
diamond wire about 40 cm long and a sample holder. Total weight could be held to as
low as 300 g. <strong>The</strong> benefit of such an <strong>in</strong>strument would be enormous. It would allow
imag<strong>in</strong>g of fresh rock surfaces (essential <strong>for</strong> m<strong>in</strong>eralogy and <strong>the</strong> detection of possible
biogenic structures). In addition, <strong>the</strong> depth of oxidation could be determ<strong>in</strong>ed <strong>in</strong>
relatively impermeable rock, allow<strong>in</strong>g extrapolation to depth of oxidation <strong>in</strong> <strong>the</strong> soil.
Analyses of completely unwea<strong>the</strong>red material with an alpha-proton-X-ray
spectrometer would also be possible. However, it will be necessary to take account of
contam<strong>in</strong>ation effects <strong>in</strong>troduced by all sample preparation techniques and to choose
materials and techniques appropriate <strong>for</strong> <strong>the</strong> subsequent observations and analyses.
Thus, a diamond saw would be totally unacceptable <strong>for</strong> prepar<strong>in</strong>g a gas
chromatograph-mass spectrometer sample <strong>in</strong>tended <strong>for</strong> a ppm-level search <strong>for</strong> carbon.
Alternatives such as boron nitride would have to be substituted, although trace
contam<strong>in</strong>ations would need to be considered.
A collection of microbial structures from Earth as a basis <strong>for</strong> comparison should be
available. Such a database would be a very helpful tool <strong>in</strong> recognis<strong>in</strong>g possible
microbial structures on Mars. This database would not only <strong>in</strong>clude images of fossil
microbes, but of m<strong>in</strong>erals <strong>the</strong> precipitation of which was <strong>in</strong>itiated by microbial
growth.
<strong>The</strong> recognition and identification of rocks and m<strong>in</strong>erals based on <strong>the</strong> same type
and quality of data that can realistically be expected from a Mars mission should be
tested and exercised us<strong>in</strong>g data (ma<strong>in</strong>ly electronic images of contents unknown to
<strong>in</strong>terpreters) given to experienced geologists etc.
Imaged materials should <strong>in</strong>clude all types of geological materials with a focus on
those most likely present on Mars. Samples should also <strong>in</strong>clude dirty, uncleaned field
material. Based on such a study, <strong>the</strong> degree of confidence obta<strong>in</strong>able by Earth-based
‘Mars field work’ and <strong>the</strong> variations caused by different <strong>in</strong>terpreters could be estimated.
• <strong>the</strong> <strong>in</strong>vestigation must have mobility to a distance of at least 20 m from <strong>the</strong> land<strong>in</strong>g
site;
• <strong>the</strong> preparation of surfaces and samples must guarantee access to unwea<strong>the</strong>red
material;
• contam<strong>in</strong>ation of samples dur<strong>in</strong>g preparation must be carefully considered;
• optical microscopy (down to a resolution of around 1 µm) and ei<strong>the</strong>r atomic <strong>for</strong>ce
microscopy or scann<strong>in</strong>g electron microscopy (down to a resolution of 0.01 µm) of
<strong>the</strong> same sample are required, although fossils may be evident at many scales;
• successful microscopy will strongly depend on <strong>the</strong> samples and <strong>the</strong>ir preparation;
• methods of sample acquisition must be as versatile as possible, enabl<strong>in</strong>g deep-core
sampl<strong>in</strong>g of sediments, core sampl<strong>in</strong>g of hard rocks and soil sampl<strong>in</strong>g;
• penetration of hard rocks is essential <strong>for</strong> petrographic characterisation, unbiased
chemical analysis and search<strong>in</strong>g <strong>for</strong> fossil microbes;
• a database with terrestrial microbial structures must be available <strong>for</strong> comparison;
• petrographic and biological <strong>in</strong>terpretation of images must be exercised under
realistic conditions;
• IR spectroscopy and <strong>the</strong>rmal emission spectroscopy are <strong>in</strong>terest<strong>in</strong>g but, <strong>for</strong> goals
focused on surface m<strong>in</strong>eralogy, Raman and Mössbauer spectroscopy may be more
appropriate. Optical spectroscopy is unlikely to produce useful results.
team III: <strong>the</strong> <strong>in</strong>spection of subsurface aliquots and surface rocks/II.6
II.6.23 Data Analysis
II.6.24 Summary of
Major Conclusions
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