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

Table II.7.4/1. Recommended Instruments <strong>for</strong> <strong>Search</strong><strong>in</strong>g <strong>for</strong> Organics on Mars.
Mass Power Volume
Instrument Analysis (kg) (W) (m 3 ) Data
Alpha/Proton/ Elemental analysis 0.5 0.4 300 16 kbit/
X-ray Spectrometer <strong>for</strong> all except H and He (1.3 peak) sample
Mössbauer Fe-bear<strong>in</strong>g m<strong>in</strong>erals 0.5 1.6 600 1.2 Mbit/
Spectrometer Fe-oxidation state and ratios sample
determ<strong>in</strong>ation of water, particularly as a function of depth. <strong>The</strong> depth profile of <strong>the</strong>
abundance of oxidants <strong>in</strong> <strong>the</strong> regolith is ano<strong>the</strong>r obvious requirement.
As yet, no organics have been found on Mars and <strong>the</strong>ir discovery and analysis
would be of prime importance <strong>for</strong> exobiology. It will be necessary, however, to
differentiate carefully between organics of an abiotic orig<strong>in</strong>, especially those of
meteoritic orig<strong>in</strong>.
On Earth, <strong>the</strong> primary biopolymers undergo a complex process of degradation and
condensation follow<strong>in</strong>g <strong>the</strong> death of <strong>the</strong> organism. <strong>The</strong> result is a complex and
chemically stable macromolecular material (kerogen). In addition, certa<strong>in</strong> stable
lipid-rich biopolymers survive this degradation process, to contribute directly to <strong>the</strong>
constitution of <strong>the</strong> kerogen. Sediments may also conta<strong>in</strong> o<strong>the</strong>r stable organic
compounds that have survived, at least <strong>in</strong> part, <strong>the</strong> processes of alteration. Many can
be classified as biomarkers on <strong>the</strong> basis of <strong>the</strong>ir structures and/or carbon isotopic
compositions. Such biomarkers and kerogens of recognisable biological orig<strong>in</strong> have
been found <strong>in</strong> sediments on Earth dat<strong>in</strong>g back at least 0.5 Gyr. It is <strong>the</strong>re<strong>for</strong>e
conceivable that such materials might be detected on Mars, given appropriate sites.
Tak<strong>in</strong>g <strong>in</strong>to account factors such as survivability, especially <strong>in</strong> an oxidis<strong>in</strong>g
environment, has led to <strong>the</strong> follow<strong>in</strong>g recommended priority order <strong>in</strong> search<strong>in</strong>g <strong>for</strong>
organics:
1. volatile low molecular weight compounds, <strong>in</strong>clud<strong>in</strong>g hydrocarbons (especially
methane), alkanoic acids and peroxy acids;
2. medium molecular weight compounds, <strong>in</strong>clud<strong>in</strong>g hydrocarbons (straight- and
branched-cha<strong>in</strong>, isoprenoids, terpenoids, steroids and aromatics);
3. macromolecular components, which would be kerogen-like components, oligoand
polypeptides.
Table II.7.4/1 lists <strong>the</strong> analysis <strong>in</strong>struments that have been identified as suitable, <strong>in</strong>
total, to cover <strong>the</strong> range of determ<strong>in</strong>ations, elemental, isotopic, and molecular,
outl<strong>in</strong>ed above.
conclusions/II.7
Laser Raman Molecular analysis of organics 1.5 1.1 250 to be
Spectrometer and m<strong>in</strong>erals (2.5 peak) determ<strong>in</strong>ed
200-3500 cm -1
& 8 cm -1 resolution
Infrared Molecular analysis of m<strong>in</strong>erals 1.0 3.5 800 to be
Spectrometer and organics determ<strong>in</strong>ed
0.8-10 µm.
Spectral resolution 100.
Spatial resolution 200 µm
Pyrolytic Gas Analyse <strong>in</strong>organic/organic 4.0 8 2.5 Mbit max
Chromatograph compounds; isotopic ratio (15 peak) 0.6 Mbit m<strong>in</strong>
and Mass Spectrometer and chirality determ<strong>in</strong>ation
183