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

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SP-1231 Fig. II.2.7/1. Early morn<strong>in</strong>g fog <strong>in</strong> <strong>the</strong> Noctis Labyr<strong>in</strong>this (10ºS/95ºW). This region, about 300 km wide, lies at <strong>the</strong> western end of Valles Mar<strong>in</strong>eris. This low-ly<strong>in</strong>g fog is probably caused by f<strong>in</strong>e water ice particles. (NASA) II.2.7 NASA-Proposed Sites <strong>for</strong> Mars Exploration 90 signature of such an SO 2 effect. In this context, it is important to mention that we do not know if <strong>the</strong> observed erosional features were <strong>for</strong>med cont<strong>in</strong>uously or dur<strong>in</strong>g <strong>in</strong>dividual periods of elevated temperatures separated by millions of years. It was mentioned above that, at present, CO 2 freezes out at <strong>the</strong> w<strong>in</strong>ter poles. This translates to very large seasonal variations <strong>in</strong> CO 2 pressure of more than 30%. <strong>The</strong> surface of Mars has an elevation range of more than 30 km, which corresponds to a pressure of 13 mbar <strong>in</strong> <strong>the</strong> Hellas bas<strong>in</strong> to 0.2 mbar on top of Olympus Mons. As <strong>in</strong> <strong>the</strong> case of water, it is unclear where <strong>the</strong> CO 2 from a massive atmosphere went. So far, <strong>the</strong>re has been no clear evidence <strong>for</strong> large quantities of carbonates <strong>in</strong> <strong>the</strong> martian soil. Loss of CO 2 to space has been observed but it is still uncerta<strong>in</strong> if <strong>the</strong> rates are high enough to lead to <strong>the</strong> present situation. <strong>The</strong> selection of sites <strong>for</strong> exobiology exploration on Mars is based on two fundamental propositions: 1. early Mars was sufficiently similar to Earth to provide a suitable environment <strong>for</strong> <strong>the</strong> <strong>in</strong>ception and development of life; 2. <strong>the</strong> basic requirements <strong>for</strong> <strong>the</strong> existence of martian liv<strong>in</strong>g systems, or <strong>the</strong>ir preservation as fossils, are comparable to those <strong>for</strong>. <strong>The</strong>se concepts lead to two doma<strong>in</strong>s of <strong>in</strong>vestigation: ext<strong>in</strong>ct and extant martian life. <strong>The</strong> o<strong>the</strong>r major aspect of <strong>the</strong> search <strong>for</strong> life on Mars is <strong>the</strong> knowledge it can provide on <strong>the</strong> precursor organic compounds, <strong>the</strong> traces of which are no longer observed on Earth because of <strong>the</strong> recycl<strong>in</strong>g of ancient rocks by plate tectonics. As no
plate tectonic evidence has been observed on Mars, it is expected that legacies of such compounds can be found <strong>in</strong> aqueous sedimentary deposits <strong>in</strong> ancient Martian cratered terra<strong>in</strong> (NASA SP-530, 1995). Water be<strong>in</strong>g <strong>the</strong> major requirement <strong>for</strong> life, seek<strong>in</strong>g life equates to search<strong>in</strong>g <strong>for</strong> traces of water activity (Greeley & Thomas, 1994). As outl<strong>in</strong>ed earlier, <strong>the</strong> present conditions on Mars do not allow <strong>the</strong> presence of liquid water on its surface. Today, liquid water may be found only beneath <strong>the</strong> surface, where <strong>the</strong>re are higher temperatures and pressures. That means at a depth of more than just a few metres and, hence, beyond <strong>the</strong> access of probes <strong>for</strong> some time to come. Consequently, we could look today only <strong>for</strong> environments where ancient life might have been preserved or <strong>for</strong> natural processes that might have brought extant subsurface life up to more accessible depths. II.2.7.1 Water and a Favourable Environment With its current th<strong>in</strong> atmosphere giv<strong>in</strong>g no UV protection and a cold, dry climate, Mars comb<strong>in</strong>es <strong>the</strong> most severe conditions <strong>for</strong> <strong>the</strong> <strong>in</strong>ception of life. However, conditions were different <strong>in</strong> <strong>the</strong> past, and evidence <strong>for</strong> water activity and aqueous sedimentary bas<strong>in</strong>s have been demonstrated (Cabrol & Gr<strong>in</strong>, 1995; Carr, 1996). <strong>The</strong> duration of water activity and liquid habitats is also a critical issue (McKay & Davis, 1991). Though <strong>the</strong> conditions might have been more favourable dur<strong>in</strong>g <strong>the</strong> first 15 Gyr of martian history, <strong>the</strong>re is no evidence that large bas<strong>in</strong>s such as Elysium were active dur<strong>in</strong>g <strong>the</strong> Amazonian era (Scott, 1995; Scott & Chapman, 1991). Even more <strong>in</strong>trigu<strong>in</strong>g is <strong>the</strong> evidence of <strong>the</strong> activation of large runoff valleys, and development of smaller-scale lakes <strong>in</strong> highland craters, such as <strong>in</strong> <strong>the</strong> Gusev and Gale craters (Cabrol et al., 1996; Gr<strong>in</strong> & Cabrol, 1997) dur<strong>in</strong>g <strong>the</strong> same geological period. Morphologic evidence show <strong>the</strong>se lakes to have existed over long periods and <strong>the</strong>y may have provided oases <strong>for</strong> life more recently. Fluvial valley networks and channels <strong>in</strong> <strong>the</strong> highlands and on volcano slopes, ancient bas<strong>in</strong>s and lakes are, <strong>the</strong>n, <strong>the</strong> best evidence of a water-rich past. This evidence, coupled with <strong>the</strong> discovery on Earth of microbiota able to survive <strong>in</strong> a Mars-analogue environment (Friedman & Ocampo, 1976) and <strong>the</strong> better understand<strong>in</strong>g of <strong>the</strong> early evolution of life on Earth, have allowed researchers to identify candidate sites <strong>for</strong> exobiological exploration on Mars (Greeley & Thomas, 1994). <strong>The</strong> selection of sites <strong>for</strong> exobiology is thus based on geologic and geomorphic evidence of paleowaterflows, ponds, ice and hydro<strong>the</strong>rmal activity. <strong>the</strong> planet mars/II.2 Fig. II.2.7/2. Frost deposit at <strong>the</strong> Vik<strong>in</strong>g-2 Lander location (48ºN/226ºW). This May 1979 image shows a coat<strong>in</strong>g of ice a few microns thick. (NASA) 91
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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
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SP-1231 22 kilometres in</s
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SP-1231 24 Laboratory Investigation
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I.3 Limits of Life
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temperatures of 95-106ºC. This sug
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(mainly found <str
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cannot exclude fin
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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
Page 41 and 42: SP-1231 Fig. I.4.2.2/4. Evaporite w
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
Page 51 and 52: SP-1231 54 I.4.3.2.1 Sedimentary Or
Page 53 and 54: SP-1231 56 The iso
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
Page 59 and 60: SP-1231 62 Klein,
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 and 72: SP-1231 74 TABLE I.6.2/1 EVIDENCE O
Page 73 and 74: SP-1231 I.6.3 What to Searc
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
Page 85: valley networks (Fig. II.2.5/2) are
Page 89 and 90: Table II.2.7.4/1. Potential Mars <s
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
Page 115 and 116: SP-1231 120 II.4.5 The</str
Page 117 and 118: SP-1231 122 II.4.6 Rovers and Drill
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Page 123 and 124: SP-1231 128 Sharp, M., Parkes, J.,
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Page 127 and 128: SP-1231 132 II.5.3 Isotopic Analysi
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Page 133 and 134: SP-1231 138 optical microscope. Bot
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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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