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

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TABLE I.6.2/2 EVIDENCE OF EXTINCT LIFE <strong>The</strong> chances of f<strong>in</strong>d<strong>in</strong>g evidence of exist<strong>in</strong>g life on a planet at this po<strong>in</strong>t are remote. We cannot reach deep below <strong>the</strong> surface with any equipment transportable on current lander missions. Nor would we know just now where to look. Perhaps a future detailed survey will identify an active surface hydro<strong>the</strong>rmal system by means of water vapour emission and a <strong>the</strong>rmal signature. If so, a specialised Lander to <strong>in</strong>vestigate that region would be warranted. At <strong>the</strong> moment, however, we must concentrate <strong>the</strong> search on evidence of ext<strong>in</strong>ct life. To that end, it will be necessary to provide <strong>the</strong> follow<strong>in</strong>g: i. clear images of groups of fossil ‘organisms'’ and high-resolution studies of <strong>in</strong>dividual structural features; ii. accompany<strong>in</strong>g geochemical and m<strong>in</strong>eralogical evidence, <strong>in</strong> <strong>the</strong> <strong>for</strong>m of biosignatures, which are related both spatially and temporally (<strong>in</strong> geological terms) with <strong>the</strong> imaged structures; iii. organic residuals, shown to be of biological orig<strong>in</strong>. O<strong>the</strong>r than <strong>the</strong>se small-scale features, we may also seek evidence of ext<strong>in</strong>ct microbial matt<strong>in</strong>g communities through <strong>the</strong> observation of macroscopically visible lam<strong>in</strong>ations, <strong>the</strong> so-called stromatolite structures. However, confirmation of a biological orig<strong>in</strong> <strong>for</strong> any such observed structures will still require, as on Earth, accompany<strong>in</strong>g <strong>in</strong><strong>for</strong>mation of <strong>the</strong> type <strong>in</strong>dicated <strong>in</strong> (ii) and (iii) above. <strong>The</strong> ma<strong>in</strong> po<strong>in</strong>ts are summarised <strong>in</strong> Tables I.6.2/1 and I.6.2/2. science and experiment strategy/I.6 1. Structural Indicators: Microscopic Observations: of groups of possible microfossil structures <strong>in</strong> sedimentary deposits, <strong>in</strong>clud<strong>in</strong>g petrological analysis of <strong>the</strong> associated m<strong>in</strong>erals and <strong>the</strong> study of any residual carbonaceous matter. Electron Microscopy: to provide nm-resolution study of <strong>the</strong> structure of possible microfossils detected by optical microscopy and to search <strong>for</strong> ‘nanofossils’. Atomic Force Microscopy: to obta<strong>in</strong> 3D images of <strong>the</strong> structure, at nm-resolution, of possible microfossils and associated material. Macroscopic Observation: of stromatolite-type biosedimentary structures <strong>in</strong> freshly exposed scarps or <strong>in</strong> rock sections, us<strong>in</strong>g a telemicroscope or telescope with IR or Raman spectroscopic capability to confirm <strong>the</strong> m<strong>in</strong>eral and carbonaceous constituents. 2. Biogeochemical Indicators: from <strong>the</strong> determ<strong>in</strong>ation of <strong>the</strong> elemental abundances <strong>in</strong> reduced (organic) carbon remnants us<strong>in</strong>g a Gas Chromatograph/Mass Spectrometer (GCMS) and Alpha-Proton-X-ray Spectrometer (APX), to give e.g. H/C ratio as <strong>in</strong>dex of aromaticity by assay of <strong>the</strong> ‘organic’ to ‘carbonate’ carbon content of fossil-conta<strong>in</strong><strong>in</strong>g sediments from an analysis of <strong>the</strong> volatile (hydrocarbon) component of <strong>the</strong> reduced carbon constituents <strong>in</strong> associated sedimentary material, us<strong>in</strong>g pyrolysis/gas chromatography/mass spectroscopy. 3. Isotopic Indicators: <strong>the</strong> enhancement of <strong>the</strong> 12C isotope to 13C dur<strong>in</strong>g conversion of <strong>in</strong>organic carbon to organic <strong>in</strong> autotrophic fixation is reta<strong>in</strong>ed <strong>in</strong> biogenic carbon residues. It provides a dist<strong>in</strong>ct biomark when compared with <strong>the</strong> <strong>in</strong>organic carbon pool. <strong>The</strong> Pyrolyser/GCMS is used. An Ion Microprobe is used <strong>for</strong> microstructures. Similarly, D/H fractionation and 34S/ 32S isotope composition change between sulphides and sulphates can be <strong>in</strong>dicators of earlier biological activity. 4. Molecular Indicators: certa<strong>in</strong> dist<strong>in</strong>ct biochemical compounds, e.g. lipid type and pigments, may withstand degradation over very long periods as part of <strong>the</strong> kerogen residue. <strong>The</strong>y may be extracted by organic solvents from residues and fossils <strong>for</strong> analysis (<strong>in</strong>clud<strong>in</strong>g chiral and isotopic) to obta<strong>in</strong> an <strong>in</strong>dication of <strong>the</strong> nature of <strong>the</strong> orig<strong>in</strong>al body. 5. Chirality Indicator: homochirality is characteristic of life and this structural feature is reta<strong>in</strong>ed on death of <strong>the</strong> organism. Racemisation proceeds very slowly under cold dry conditions such as now exist on Mars. An optical rotation detector is used. 6. Spectral Observations: vibrational spectra of organic compounds provide a valuable analytical tool which can be applied to help unravel <strong>the</strong> nature of sedimentary carbonaceous samples of biological and abiotic orig<strong>in</strong>. It also is able to identify <strong>the</strong> m<strong>in</strong>eralogical content of <strong>the</strong> associated sediment. IR and Raman spectroscopy predom<strong>in</strong>ate and can be <strong>in</strong>cluded <strong>in</strong> <strong>the</strong> microscopy. I.6.2 What to <strong>Search</strong> For? 75
SP-1231 I.6.3 What to <strong>Search</strong> With? 76 <strong>The</strong> preced<strong>in</strong>g Tables <strong>in</strong>dicate <strong>the</strong> types of <strong>in</strong>strumentation that would normally be required <strong>in</strong> order to search <strong>for</strong> <strong>the</strong> evidence of extant and ext<strong>in</strong>ct life on Mars. Focus<strong>in</strong>g upon <strong>the</strong> evidence <strong>for</strong> ext<strong>in</strong>ct life, we have <strong>the</strong> follow<strong>in</strong>g requirements: 1. Optical Microscope, with a range from medium- to high-power to cover sample selection through to high-resolution observation of larger ‘fossil’-like structures and associated m<strong>in</strong>erals. 2. IR or Raman Spectrometer, designed to work <strong>in</strong> conjunction with <strong>the</strong> microscope system <strong>for</strong> analysis of <strong>in</strong>dividual gra<strong>in</strong>s and any associated organic material. 3. Atomic Force Microscope, allied to <strong>the</strong> stage of <strong>the</strong> optical microscope, to exam<strong>in</strong>e <strong>in</strong> 3D <strong>in</strong> <strong>the</strong> nm-range selected elements of <strong>the</strong> microscope field conta<strong>in</strong><strong>in</strong>g possible fossils. 4. Alpha-Proton-X-ray Spectrometer, to carry out elemental analysis (exclud<strong>in</strong>g H), on m<strong>in</strong>erals associated with ‘fossil’ sediments and on any associated carbonaceous material. 5. Gas Chromatograph/Mass Spectrometer, to analyse <strong>the</strong> volatiles from carbon residues, to provide elemental, molecular, and isotopic abundances, and compositions. Various types of vaporisers can be used. 6. Ion Microprobe, could be valuable, <strong>in</strong> conjunction with <strong>the</strong> microscope, to analyse specific regions of <strong>the</strong> samples that are associated with ‘fossils’ and to give structurally def<strong>in</strong>ed 13 C/ 12 C ratios <strong>for</strong> organic traces. 7. Homochirality detector, to search <strong>for</strong> optical activity. This may be a dedicated optical <strong>in</strong>strument us<strong>in</strong>g a liquid sample or it may be simply a chiral column <strong>in</strong>cluded <strong>in</strong> <strong>the</strong> gas chromatograph. 8. Telescope, to search <strong>for</strong> macrostructures of possible biological orig<strong>in</strong> <strong>in</strong> cleaved rocks or at outcrops. It would need to be associated with a spectroscopic capability. Clearly, it will not be feasible to carry all of <strong>the</strong>se <strong>in</strong>struments on a s<strong>in</strong>gle small Lander. In mak<strong>in</strong>g a selection of <strong>the</strong> <strong>in</strong>struments to <strong>for</strong>m a unified package we have been conscious of <strong>the</strong> need to use <strong>in</strong>struments that have already flown or are under development <strong>for</strong> flight. In that context, we have looked to <strong>the</strong> European <strong>in</strong>struments that are already associated with a Mars programme or are be<strong>in</strong>g produced <strong>for</strong> a relevant ESA mission, such as Rosetta. From that analysis, <strong>the</strong> follow<strong>in</strong>g <strong>in</strong>struments were identified <strong>for</strong> fur<strong>the</strong>r study at this po<strong>in</strong>t (o<strong>the</strong>rs, especially a spectrometer, may be considered later if circumstances change): Optical Telemicroscope Alpha, Proton, X-ray Spectrometer Atomic Force Microscope Gas Chromatograph/Mass Spectrometer Homochirality Detector
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SP-1231 Exobiology
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Cover Fossil coccoid bacteria, 1 µ
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4 I.5 Potential Non-Martian Sites <
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6 6.2 Imaging of F
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The Exobio
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pyrolysis, or similar techniques, f
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Ignasi Casanova, Institute
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I AN EXOBIOLOGICAL VIEW OF THE SOLA
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SP-1231 18 surface pressure of CO 2
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SP-1231 20 10 bar befor</st
Page 21 and 22: SP-1231 22 kilometres in</s
Page 23 and 24: SP-1231 24 Laboratory Investigation
Page 25 and 26: I.3 Limits of Life
Page 27 and 28: temperatures of 95-106ºC. This sug
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Page 31 and 32: cannot exclude fin
Page 33 and 34: Responses to Cosmic Radiation <stro
Page 35 and 36: acid to identify the</stron
Page 37 and 38: Horneck, G. (1993). Responses of Ba
Page 39 and 40: SP-1231 Fig. I.4.2.2/1. Size distri
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Page 43 and 44: SP-1231 Fig. I.4.2.3/1A (left). Net
Page 45 and 46: SP-1231 48 A detailed chemical anal
Page 47 and 48: SP-1231 Fig. I.4.3.1.1/1. Scheme of
Page 49 and 50: SP-1231 Fig. I.4.3.1.2/1. A: Compar
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Page 55 and 56: SP-1231 Fig. I.4.3.2.3/1. Cholester
Page 57 and 58: SP-1231 60 References regard to non
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Page 61 and 62: SP-1231 64 ities in</strong
Page 63 and 64: SP-1231 Fig. I.5.1.1/1. A 34×42 km
Page 65 and 66: SP-1231 Fig. I.5.2.1/1. Titan’s a
Page 67 and 68: SP-1231 Fig. I.5.2.2/2. Modelled Ti
Page 69 and 70: SP-1231 72 Galileo: images availabl
Page 71: SP-1231 74 TABLE I.6.2/1 EVIDENCE O
Page 75 and 76: SP-1231 78 I.7.3 Organic Chemistry
Page 77 and 78: II.1 Introduction The</stro
Page 79 and 80: II.2 The Planet Ma
Page 81 and 82: cover the range 4.
Page 83 and 84: The depletion of c
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Page 87 and 88: plate tectonic evidence has been ob
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Page 91 and 92: II.3 The Martian M
Page 93 and 94: principal atmosphe
Page 95 and 96: Lines of evidence
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Page 101 and 102: Anders, E. (1989). Prebiotic organi
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Page 113 and 114: SP-1231 118 orbital characteristics
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Page 117 and 118: SP-1231 122 II.4.6 Rovers and Drill
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SP-1231 128 Sharp, M., Parkes, J.,
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SP-1231 Fig. II.5.1/1. The<
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SP-1231 132 II.5.3 Isotopic Analysi
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SP-1231 134 chemical composition de
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SP-1231 Fig. II.5.7.1/1. Th
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SP-1231 138 optical microscope. Bot
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SP-1231 140 protons of discrete ene
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SP-1231 142 atures should be per<st
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SP-1231 Fig. II.5.7.7/1. Example of
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SP-1231 146 soils. In this approach
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SP-1231 148 discrimin</stro
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SP-1231 150 determin</stron
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SP-1231 Fig. II.5.10.2/2. Enantiome
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SP-1231 154 References achiral colu
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II.6 Team III: The
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in width and heigh
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Searchin</
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minerals or oxidat
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A second group of rocks, however, m
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SCIENTIFIC METHOD AND REQUIREMENTS
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The sample materia
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surprising. To ach
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The main</
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Consideration of a diamond wire-saw
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Schoonen, M.A. & Barnes, H.L. (1991
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SP-1231 180 II.7.2 The</str
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SP-1231 Fig. II.7.4/1. Look
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SP-1231 184 II.7.5 A Possible <stro
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Team IV was asked to examin
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