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

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SP-1231 168 II.6.9 High-Resolution Studies Pathf<strong>in</strong>der (IMP) provided an excellent balance between resolution, colour <strong>in</strong><strong>for</strong>mation and data volume. We propose to follow a similar strategy. In order to def<strong>in</strong>e <strong>the</strong> shape of <strong>the</strong> spectral reflectance curve, a m<strong>in</strong>imum of n<strong>in</strong>e filters is required (440, 530, 600, 700, 800, 900, 930, 960 & 1000 nm). This will allow us to search <strong>for</strong> potentially <strong>in</strong>terest<strong>in</strong>g targets with absorption bands <strong>in</strong> <strong>the</strong> 900-1000 nm region of <strong>the</strong> spectrum. An additional set of three filters is required to provide <strong>in</strong><strong>for</strong>mation on <strong>the</strong> optical depth. Two o<strong>the</strong>r filters need to be set aside to provide red/blue stereo coverage. We note that attempt<strong>in</strong>g to acquire a stereo pair at different times may save a filter position. However, <strong>the</strong> change <strong>in</strong> <strong>the</strong> illum<strong>in</strong>ation between <strong>the</strong> acquired images would need to be carefully considered and modelled. <strong>The</strong> uncerta<strong>in</strong>ties <strong>in</strong> this process are probably too large and hence dedicated stereo pairs are required. Thus, <strong>the</strong> system needs a m<strong>in</strong>imum of 14 positions. In order to quantify both atmospheric phenomena and to provide a survey of <strong>the</strong> entire scene, <strong>the</strong> system needs to be articulated <strong>in</strong> both azimuth and elevation. Us<strong>in</strong>g current detector devices (1000×1000-pixel frame transfer CCDs) and a pixel scale of 1 mrad px -1 (equivalent to <strong>the</strong> IMP), a 40×40º field of view can be acquired <strong>in</strong> one frame. An estimated daily telemetry requirement of 8 Mbit would be necessary. Highquality once-only products, such as surveys, require around 275 Mbit. It needs to be emphasised that present developments <strong>in</strong> micro-<strong>in</strong>tegrated camera systems have concentrated on <strong>the</strong> CCD and accompany<strong>in</strong>g readout electronics. <strong>The</strong>se developments have driven <strong>the</strong> total mass of <strong>the</strong>se elements to around 50 g. However, <strong>the</strong> panoramic survey camera requires a higher dynamic range, azimuth and elevation motors (cover<strong>in</strong>g almost 4π steradians), a mast and a significant filter wheel assembly. Acousto-optical tunable filters might be used to reduce <strong>the</strong> mass of <strong>the</strong> latter but <strong>the</strong>y are currently not available <strong>in</strong> large enough dimensions to cover a 1000×1000-pixel focal plane. We <strong>the</strong>re<strong>for</strong>e conservatively assume a mass of 2.5 kg <strong>for</strong> this system and a power requirement of 8 W. <strong>The</strong> calibration of <strong>the</strong> panoramic camera requires additional hardware to be deployed on <strong>the</strong> lander. <strong>The</strong> Mars Pathf<strong>in</strong>der camera used a series of black and white and colour calibration targets to provide good cross-calibration between <strong>the</strong> image frames acquired at different times and to validate <strong>the</strong> pre-flight calibration. A similar approach should be adopted. Places on <strong>the</strong> lander, <strong>in</strong> view of <strong>the</strong> camera and see<strong>in</strong>g as large a solid angle of <strong>the</strong> sky as possible, should be set aside <strong>for</strong> a calibration target. <strong>The</strong> target should be large enough: 100 pixels across seen from <strong>the</strong> camera. Consideration should be given to whe<strong>the</strong>r <strong>the</strong> rover can deploy a calibration target away from <strong>the</strong> lander <strong>in</strong> order to m<strong>in</strong>imise scattered light contributions from <strong>the</strong> lander’s body and to allow full sky illum<strong>in</strong>ation of <strong>the</strong> target. II.6.9.1 Objectives After specific areas of <strong>in</strong>terest have been identified by <strong>the</strong> panoramic survey, a detailed <strong>in</strong>vestigation needs to be per<strong>for</strong>med. This should be by a rover (or some o<strong>the</strong>r mobile device) mov<strong>in</strong>g to an area of <strong>in</strong>terest and obta<strong>in</strong><strong>in</strong>g higher resolution data from <strong>the</strong> target’s proximity. A primary requirement of this <strong>in</strong>vestigation is knowledge of <strong>the</strong> detailed optical appearance. This must determ<strong>in</strong>e <strong>the</strong> morphological structure of a target, its colour, <strong>the</strong> degree of wea<strong>the</strong>r<strong>in</strong>g and <strong>the</strong> dust coverage. This will determ<strong>in</strong>e how much <strong>the</strong> material has been chemically or physically processed, allow a better assessment of its orig<strong>in</strong>, and help to identify an even more detailed target <strong>for</strong> gr<strong>in</strong>d<strong>in</strong>g and/or sampl<strong>in</strong>g and subsequent detailed <strong>in</strong>vestigation. This implies that a simplified camera system with colour capability needs to be on <strong>the</strong> mobile device. It is generally accepted that microscopic <strong>in</strong>vestigation of an unprepared surface provides little useful additional <strong>in</strong><strong>for</strong>mation (see Part I). If a surface can be physically prepared (by gr<strong>in</strong>d<strong>in</strong>g or polish<strong>in</strong>g), however, a microscope with front side illum<strong>in</strong>ation can <strong>in</strong>vestigate <strong>the</strong> material’s microstructure. This will allow an assessment of <strong>in</strong>clusions <strong>in</strong> <strong>the</strong> rock and place constra<strong>in</strong>ts on <strong>the</strong> processes that <strong>for</strong>med <strong>the</strong> rock. Colour capability is important s<strong>in</strong>ce it will allow us to differentiate between <strong>in</strong>dividual m<strong>in</strong>erals. We note that polarisation measurements are useful only <strong>in</strong> transmission.
<strong>The</strong> sample materials should be subjected to microscopy with <strong>the</strong> follow<strong>in</strong>g aims, as discussed <strong>in</strong> Section II.5: – determ<strong>in</strong>e <strong>the</strong> m<strong>in</strong>eralogy; – determ<strong>in</strong>e <strong>the</strong> texture of rock and soil fragments; – search <strong>for</strong> possible biogenic structures. Results will allow <strong>the</strong> def<strong>in</strong>ition of <strong>the</strong> geological framework <strong>for</strong> any found biogenic structures or biochemical signatures. <strong>The</strong> <strong>in</strong>terpretation of images will largely rely on experience ga<strong>in</strong>ed by imag<strong>in</strong>g terrestrial materials with a system provid<strong>in</strong>g identical image quality. Exchange of images with unknown content should be per<strong>for</strong>med between at least two groups well be<strong>for</strong>e land<strong>in</strong>g on Mars. <strong>The</strong> search <strong>for</strong> possible biological structures will be supported by a collection of images of m<strong>in</strong>eralised terrestrial analogues that is currently be<strong>in</strong>g built up. As <strong>the</strong> nature of martian life is unknown, <strong>the</strong> search can only be based on knowledge of Earth materials. With<strong>in</strong> sedimentary material, evidence might be sought <strong>for</strong> layer<strong>in</strong>g, ve<strong>in</strong>s with<strong>in</strong> <strong>the</strong> rocks, amugdules, botryoidal surfaces, mottl<strong>in</strong>g, bleach<strong>in</strong>g, geopetal features and filamentary or ropy structures. Studies of microfossils on Earth show that evidence <strong>for</strong> past life can exist at all scales and, <strong>the</strong>re<strong>for</strong>e, by prob<strong>in</strong>g <strong>in</strong>creas<strong>in</strong>gly smaller scales <strong>the</strong> chances of discovery <strong>in</strong>crease. Examples of microfossils found on Earth at relatively low resolution were given <strong>in</strong> Figs. II.6.2/1, II.6.2.1/1 & II.6.2.1/2. <strong>The</strong> search <strong>for</strong> microbial remnants should be made with <strong>the</strong> highest spatial resolution that can be reasonably achieved on a small rover. We estimate this to be better than
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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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Horneck, G. (1993). Responses of Ba
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SP-1231 Fig. I.4.2.2/1. Size distri
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SP-1231 Fig. I.4.2.2/4. Evaporite w
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SP-1231 Fig. I.4.2.3/1A (left). Net
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SP-1231 48 A detailed chemical anal
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SP-1231 Fig. I.4.3.1.1/1. Scheme of
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SP-1231 Fig. I.4.3.1.2/1. A: Compar
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SP-1231 54 I.4.3.2.1 Sedimentary Or
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SP-1231 56 The iso
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SP-1231 Fig. I.4.3.2.3/1. Cholester
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SP-1231 60 References regard to non
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SP-1231 62 Klein,
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SP-1231 64 ities in</strong
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SP-1231 Fig. I.5.1.1/1. A 34×42 km
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SP-1231 Fig. I.5.2.1/1. Titan’s a
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SP-1231 Fig. I.5.2.2/2. Modelled Ti
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SP-1231 72 Galileo: images availabl
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SP-1231 74 TABLE I.6.2/1 EVIDENCE O
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SP-1231 I.6.3 What to Searc
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SP-1231 78 I.7.3 Organic Chemistry
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II.1 Introduction The</stro
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II.2 The Planet Ma
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cover the range 4.
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The depletion of c
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valley networks (Fig. II.2.5/2) are
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plate tectonic evidence has been ob
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Table II.2.7.4/1. Potential Mars <s
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II.3 The Martian M
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principal atmosphe
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Lines of evidence
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indicated by carbo
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quest for
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Anders, E. (1989). Prebiotic organi
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Urey, H.C. (1968). Origin</
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SP-1231 Fig. II.4.1.1/1. A Gilbert-
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SP-1231 Fig. II.4.1.3/1. Th
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SP-1231 114 Sinuou
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Page 161: SCIENTIFIC METHOD AND REQUIREMENTS
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