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

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I.5.1.3 O<strong>the</strong>r Icy Satellites Several o<strong>the</strong>r icy bodies have experienced episodes of tidal heat<strong>in</strong>g, and moreover <strong>the</strong>y would have had hotter <strong>in</strong>teriors <strong>in</strong> <strong>the</strong> distant past when radioactive decay was a more potent heat source. Saturn’s small satellite Enceladus has terra<strong>in</strong>s where <strong>the</strong> impact crater record has been erased by recent resurfac<strong>in</strong>g. This <strong>in</strong>dicates an episode of enhanced tidal heat<strong>in</strong>g that could have supported hydro<strong>the</strong>rmal life. Indirect evidence that hydro<strong>the</strong>rmal reactions have occurred <strong>in</strong> icy satellites comes from <strong>the</strong> apparent absence of carbon monoxide and <strong>the</strong> preponderance of methane <strong>in</strong> outer <strong>Solar</strong> <strong>System</strong> ices (Simonelli et al., 1989). This could have been caused by <strong>the</strong> oxidation of rock, and may have been organically mediated. Neptune’s large satellite Triton has abundant methane and a degree of relatively recent cryovolcanic resurfac<strong>in</strong>g and ongo<strong>in</strong>g geyser activity (Soderblom et al., 1990) that make it <strong>the</strong> most entic<strong>in</strong>g target beyond Saturn, as discussed below. I.5.2.1 <strong>The</strong> Titan Atmosphere Titan’s atmosphere was revealed ma<strong>in</strong>ly by <strong>the</strong> Voyager-1 mission <strong>in</strong> 1980, which yielded <strong>the</strong> bulk composition (90% molecular nitrogen and about 1-8% methane). Also, a great number of trace constituents were observed <strong>in</strong> <strong>the</strong> <strong>for</strong>m of hydrocarbons (acetylene, ethane, ethylene, etc) nitriles (HCN, C 2N 2, HC 3N) and oxygen compounds (CO and CO 2). Recent analysis of <strong>the</strong> Voyager-1 spectroscopic data provided precise potential non-martian sites <strong>for</strong> extraterrestrial life/I.5 Fig I.5.1.1/2. An 80×95 km area of Europa where <strong>the</strong> youngest features are domes that are probably viscous cryovolcanic flows or sites of shallow <strong>in</strong>trusion. Ei<strong>the</strong>r explanation would make <strong>the</strong>se features good sites to search <strong>for</strong> traces of life. (Galileo image released 18 April 1997, NASA.) I.5.2 Titan 67
SP-1231 Fig. I.5.2.1/1. Titan’s atmospheric longitud<strong>in</strong>al composition variations. (From Coustenis & Bézard, 1995.) Fig. I.5.2.1/2. Variation with latitude of <strong>the</strong> temperature of Titan’s upper atmosphere. (From Coustenis & Bézard, 1995.) 68
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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
Page 13 and 14: Ignasi Casanova, Institute
Page 15 and 16: I AN EXOBIOLOGICAL VIEW OF THE SOLA
Page 17 and 18: SP-1231 18 surface pressure of CO 2
Page 19 and 20: 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
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
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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: SP-1231 Fig. I.5.1.1/1. A 34×42 km
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Page 69 and 70: SP-1231 72 Galileo: images availabl
Page 71 and 72: SP-1231 74 TABLE I.6.2/1 EVIDENCE O
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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 and 86: valley networks (Fig. II.2.5/2) are
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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SP-1231 120 II.4.5 The</str
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SP-1231 122 II.4.6 Rovers and Drill
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SP-1231 124 Site 2: Apolin<
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SP-1231 126 Site 4: Chasma area, ea
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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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Exobiology in the Solar System & The Search for Life on Mars - ESA

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