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

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SP-1231 92 A list of basic exploratory features <strong>for</strong> exobiology sites has been developed by Farmer & DesMarais: Deposits Features Fluvial Dendritic dra<strong>in</strong>age networks: simple; complex (higher order) Channel morphology: widen<strong>in</strong>g down slope; meander<strong>in</strong>g; flood pla<strong>in</strong>s; stream terraces Accessibility: layer<strong>in</strong>g visible; impact craters Lacustr<strong>in</strong>e Dra<strong>in</strong>age bas<strong>in</strong> fed by: simple channels; complex channels; Shorel<strong>in</strong>e features: lake terraces; deltas Accessibility: lava flows; aeolian cover; impact craters <strong>The</strong>rmal spr<strong>in</strong>g Dra<strong>in</strong>age system: simple channels; po<strong>in</strong>t source Localised heat source: surface (volcanic centre); subsurface <strong>the</strong>rmokarst Surface ice High latitude (>60º): lam<strong>in</strong>ated terra<strong>in</strong> Subsurface ice Mid-latitude (30-60º): patterned ground; alases; p<strong>in</strong>gos; fluidised crater ejecta. (After J.D. Farmer & D.J. DesMarais (1994). In Mars Land<strong>in</strong>g Site Catalogue, (Eds. R. Greeley & P.E. Thomas), NASA RP-1238, 2nd Edition; with permission of <strong>the</strong> editors.) II.2.7.2 Exploration <strong>for</strong> Ext<strong>in</strong>ct <strong>Life</strong> If Mars and Earth did actually experience broadly comparable conditions dur<strong>in</strong>g <strong>the</strong> first 1.5 Gyr of <strong>the</strong>ir histories, <strong>the</strong>n it is likely that life appeared dur<strong>in</strong>g that same period. Evidence of such life on Mars may be preserved <strong>in</strong> <strong>the</strong> <strong>for</strong>m of fossils and <strong>in</strong> various biosignatures. In <strong>the</strong> NASA studies <strong>for</strong> site selection <strong>for</strong> exopalaeontology, priority is given to land<strong>in</strong>g sites <strong>in</strong> ancient terra<strong>in</strong>s where hydrological systems <strong>in</strong>volv<strong>in</strong>g liquid water appear to have been long-lived and which exhibit a high probability of hav<strong>in</strong>g surficial aqueous m<strong>in</strong>eral deposits. Preference is given to m<strong>in</strong>eral deposits that might have had a long residence time <strong>in</strong> <strong>the</strong> martian crust, i.e. those that are diagenetic stable and resistant to chemical wea<strong>the</strong>r<strong>in</strong>g. On Earth, m<strong>in</strong>eralisation occurred <strong>in</strong> many Precambrian examples very rapidly, prior to cellular decomposition, and probably when organisms were still viable. <strong>The</strong> best preservation is observed where organic materials were rapidly perfused with f<strong>in</strong>e-gra<strong>in</strong>ed silica or phosphate. Evaporites <strong>for</strong>m ano<strong>the</strong>r group of potential host phases. Whereas on Earth <strong>the</strong>se are readily dissolved <strong>in</strong> hydrologic cycles, <strong>in</strong> <strong>the</strong> very dry martian climate <strong>the</strong>ir residence time might be prolonged. Hydro<strong>the</strong>rmal systems are excellent targets <strong>for</strong> a search <strong>for</strong> fossil records of biological activity. Volcanic terra<strong>in</strong>s are abundant on Mars and <strong>the</strong>re is ample evidence <strong>for</strong> ground water or ground ice. <strong>The</strong>ir comb<strong>in</strong>ation is <strong>the</strong> basis of hydro<strong>the</strong>rmal activity, which <strong>the</strong>re<strong>for</strong>e should also be abundant on Mars. <strong>The</strong> NASA search <strong>for</strong> ext<strong>in</strong>ct life (fossils) strategy on Mars <strong>the</strong>re<strong>for</strong>e gives priority to <strong>the</strong>rmal spr<strong>in</strong>g sites, which should also provide a good preservation environment <strong>for</strong> microbial fossils and to stable lacustr<strong>in</strong>e environments and outflow channel deposits. <strong>The</strong>se types of sites give almost a planetwide range <strong>for</strong> exploration (Greeley & Thomas 1994). II.2.7.3 Exploration <strong>for</strong> Extant <strong>Life</strong> Extant life, if present, probably resides <strong>in</strong> subsurface habitats where liquid water might be present and, hence, would be most likely of a chemosyn<strong>the</strong>tic <strong>for</strong>m. It seems possible that recent flows of subsurface water have brought such organisms <strong>in</strong>to nearsurface environments where <strong>the</strong>y have been cyropreserved <strong>in</strong> ground ice. It has been suggested that microorganisms may survive <strong>in</strong> ground ice <strong>for</strong> millions of years and <strong>in</strong> evaporite deposits <strong>for</strong> hundreds of million of years. Never<strong>the</strong>less, <strong>the</strong> highest priority
Table II.2.7.4/1. Potential Mars <strong>Exobiology</strong> Land<strong>in</strong>g Sites. Region (site name) Location Priority Fluvio-lacustr<strong>in</strong>e Eridania NW 37.0ºS / 230.0ºW h Parana Valles 22.0ºS / 11.0ºW h Mare Tyrrhenum 22.8ºS / 230.0ºW h Terra Tyrrhenum 24.8ºS / 285.8ºW h Aeolis SE 15.5ºS / 184.5ºW h Aeolis NE (Gusev) 7.3ºS / 305.0ºW h Iapygia NW 8.5ºS / 159.5ºW h Mangala Valles 6.3ºS / 149.5ºW h Ismenius Laous SW 33.5ºN / 342.5ºW h S<strong>in</strong>us Sabeus NE 8.0ºS / 335.0ºW h/m Diacria SE 39.5ºN / 135.5ºW m Iapygia 11.0ºS / 279.5ºW m Terra Cimmeria 43.2ºS / 208.1ºW m Candor Mensa 6.05ºS / 73.75ºW m Eridania SE 57.0ºS / 197.0ºW m Ares 2.0ºN / 16.0ºW m Hebes Chasma 1.5ºS / 76.5ºW m Memnonia NW 14.5ºS / 175.0ºW m Phasthontis NC 37.5ºS / 146.0ºW m Oxia Palu NE 21.3ºN / 0.8ºW m <strong>The</strong>rmal spr<strong>in</strong>g Dao Vallis 33.2ºS / 88.4ºW h Ares 2.0ºN / 16.0ºW m Ground ice Ismenius Lacusm SC 44.3ºN / 333.0ºW h Cassius SE 38.0ºN / 256.0ºW m Oxia Palus NW 21.1ºN / 36.7ºW m h=high, m=moderate. Adapted, by permission of <strong>the</strong> editors, from Table 5.4 p16, <strong>in</strong> Mars Land<strong>in</strong>g Site Catalogue (Eds. R. Greeley & P.E. Thomas), NASA RP-1238, 2nd Edition, 1994. <strong>in</strong> <strong>the</strong> search <strong>for</strong> extant life has <strong>the</strong> very youngest martian terra<strong>in</strong>s at high latitudes, <strong>in</strong>clud<strong>in</strong>g <strong>the</strong> north polar cap, as an objective. However, <strong>the</strong> recent ice-covered lacustr<strong>in</strong>e activity <strong>in</strong> <strong>the</strong> <strong>in</strong>tertropical band of Mars may also offer potential <strong>for</strong> extant life exploration. Ice-covered lakes, such as those that developed <strong>in</strong> <strong>the</strong> Gusev and Gale craters, had <strong>the</strong>ir f<strong>in</strong>al activity dur<strong>in</strong>g <strong>the</strong> Amazonian era but, at least <strong>for</strong> Gusev, it has been shown that lakes may have occupied <strong>the</strong> crater episodically s<strong>in</strong>ce its <strong>for</strong>mation dur<strong>in</strong>g <strong>the</strong> Early Noachian period (Cabrol et al., 1996). In Gusev, as <strong>in</strong> o<strong>the</strong>r comparable sites, life<strong>for</strong>ms may have had <strong>the</strong> opportunity to adapt <strong>in</strong> <strong>the</strong> icecovered lakes environment and to survive up to <strong>the</strong> present, especially if <strong>the</strong> presence of ice-cored (p<strong>in</strong>go-like) structures is confirmed by <strong>the</strong> Mars Global Surveyor mission. Thus, new concepts of drill<strong>in</strong>g and wells may enable us to discover oases of life <strong>in</strong> <strong>the</strong> subsurface, even at mid-latitudes. II.2.7.4 NASA Priority Land<strong>in</strong>g Sites <strong>for</strong> <strong>Exobiology</strong> Consider<strong>in</strong>g <strong>the</strong> new developments and results <strong>in</strong> exobiology and martian geology, NASA has established a list of priority sites <strong>for</strong> <strong>the</strong> search of life on Mars. <strong>The</strong> list is presented <strong>in</strong> Table II.2.7.4/1 by courtesy of <strong>the</strong> NASA Ames Research Center (contribution of Dr. N. Cabrol). <strong>the</strong> planet mars/II.2 93
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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
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acid to identify the</stron
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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
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Page 49 and 50: SP-1231 Fig. I.4.3.1.2/1. A: Compar
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Page 61 and 62: SP-1231 64 ities in</strong
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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
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Page 117 and 118: SP-1231 122 II.4.6 Rovers and Drill
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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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