An integrated exobiology package for the search for life on Mars

Pergamon

A& &xe Res. Vol. 23, No. 2, pp. 301-308, 1999 0 1999 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-l 177/99 $20.00 + 0.00 Pk SO273-1177(99)0005 l-4

AN INTEGRATED EXOBIOLOGY FOR LIFE ON MARS

PACKAGE FOR THE SEARCH

A. Brackl, P. Clancy2, B. Fitton3, B. Hofmannd, G. Horneckj, G. Kurat6, J. Maxwel17, G. Oris, C. PillingeP, F. RaulinlO, N. Thomas1 l, and F. Westall12 1 Centre de Biophysique Mol&ulaire, CNRS, Orlkans, France 2 ESA-ESTEC, Noordwijk, The Netherlands 3 ESC, Noordwijk, The Netherlands 4 Naturhistorishes Museum, Bern, Switzerland 5 Institute of Aerospace Medicine, DLR, Porz- Wahn, Germany, 6 Naturhistorishes Museum, Wien, Austria 7 Chemistry Department, Bristol University, Bristol, England 8 Dipartimento di Scienze, Universita d Xnnunzio, Pescara, Ita& 9 Planetary Science Research Institute, Open University, Milton Keynes, England lo LISA, CNRS & Universittfs Paris 12 & 7, Cre’teil, France 11 MPIji’ir Aeronomie, Lindau, Germany l2 Planetary Sciences Branch, NASA-Johnson Space Centre, Houston, USA

ABSTRACT A multi-user integrated suite of instruments designed to optimize the search for evidence of life on Mars is described. The package includes: * Surface inspection and surface environment analysis to identify the potential Mars landing sites, to inspect the surface geology and mineralogy, to search for visible surficial microbial macrofossils, to study the surface radiation budget and surface oxidation processes, to search for niches for extant life. * Analysis of surface and subsurface minerals and organics to characterize the surface mineralogy, to analyse the surface and subsurface oxidants, to analyze the mineralogy of subsurface aliquots, to analyze the organics present in the subsurface aliquots (elemental and molecular composition, isotopes, chirality). * Macroscopic and microscopic inspection of subsurface aliquots to search for life’s indicators (paleontological, biological, mineralogical) and to characterize the mineralogy of the subsurface aliquots. The study is led by ESA Manned Spaceflight and Microgravity Directorate. 01999 COSPAR. Published by Elsevier Science Ltd. INTRODUCTION In 1997, on the initiative of the ESA Manned Spaceflight and Microgravity Directorate, the ESA Exobiology Science Team carried out an extensive and broad study on the search for life in the solar system (Brack et al, 1997). ESA recommended to extend this work to a study specifically devoted to Mars, including the selection of potential sites for exobiology searches and of an integrated instrumentation package to search for life extant as well as extinct in the Martian soil. The ESA Exobiology Science Team is composed of European experts in radiation biology, planetary geology, geochemistry, mineralogy, and meteorology, as well as exobiology, since each of these science areas has considerable relevance in any attempt to search for life elsewhere and to study its origins. They were assisted by several scientific Advisors, who were able to provide additional expertise in various areas. 301

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The work of the Team is supported and directed by the Manned Spaceflight and Microgravity Directorate. On this occasion the Team was requested to carry out a study of the experimental strategy and the instrumentation necessary to search for indicators of life, especially extinct life, on or within the surface of Mars. Included in that would be a search for organic and pre-biotic organic compounds. It was assumed that such a search would be carried out using a Mars Lander and a small Rover vehicle. This was the first time that a study of this subject had been performed in depth within a purely European context. The results, in their detail, reflect in some degree that particular context. However, within the wider scientific framework there was inevitably much in the discussions and the conclusions which would be familiar to those who participated in the earlier Workshops and Meetings in the United States on this and closely related topics. The science and the basic problems remain international. NASA has undertaken several related studies, lately with increasing emphasis on the future of a manned mission to Mars. The ESA Team has briefly examined this particular issue, commenting in the Annex upon the value of Manned assistance to exobiology research on Mars, but the emphasis of this study remained that of unmanned in-situ experimentation. The NASA report on ‘An Exobiological Strategy for Mars Exploration’ (NASA SP 530), concluded that ‘The most immediate instrumentation needs are the following: Design and construction of instrumentation for in-situ mineralogical identification, description of the micro environment (including oxidant distribution), and detection and characterization of organic matter; development of a capability for acquiring samples from a depth of several metres in the regolith and from the interiors of rocks, and early deployment of the above.’ The ESA Team, starting independently from a review of the science issues, arrived at similar general conclusions, but with additional emphasis on in-situ observational studies using microscopy and with a strong recommendation to focus the discussion of landing sites much more towards the needs of exobiology exploration. The detailed recommendations on instrumentation reflect not only the scientific needs but also existing European capabilities. In principle, all of the recommended instruments could be developed in Europe, in most cases from equipment with a space heritage. Some, such as the APX, the Mijssbauer spectrometer, and the cameras, have already flown or are scheduled for flight on Mars missions.

EXPERIMENTATION

STRATEGY

The basic principles are: - to increase the chances of detecting biosignatures, whether chemical or morphological, by carefully selecting a set of potential landing sites having environments of high exobiology potential. - to provide for sampling of that environment from a range of locations and from positions where the effects of surface oxidation processes should be reduced. - to subject those.samples to an integrated set of measurements which, taken together, reduce the chances of ambiguity in the interpretation of potential biosignatures. Site definition is of course finally constrained by mission and technical factors. The sites (Table 1) were selected on the basis of a high potential exobiology significance, on currently available information, with some constraints on latitude and size. The lack of mineralogical mapping still limits the site selection process. The results from future detailed orbital surveys may therefore lead to a change in this list : Oxidation effects at the surface are assumed to be responsible for the negative results so far in the search for organics. Both direct photochemical and chemical processes have been shown theoretically to be likely, with hydrogen peroxide as a major chemical agent. As yet no in-situ measurements have been carried out and this remains as one of the goals of this experiment system. The influence of the oxidation process is expected to be limited in sedimentary rocks to the first few centimetres below the weathered outer ‘rind’, although no studies are as yet available to confirm this. ESA intends to fund a detailed study of this particular problem. Theoretical analysis of hydrogen peroxide diffusion reactions into the Mars regolith by U.S. scientists have provided values of penetration ranging from over a metre to several tens of metres. The influence of churning of the regolith by meteoritic bombardment over geological timescales remains a major uncertainty in any such calculations.

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Table 1. Selected sites on Mars for in situ exobiological exploration

Subsurface sampling by percussive core drilling into the regolith and performing analysis of sequentially presented samples will provide the essential information on the variation of oxidation state with depth. That will be in addition to a morphological, elemental, isotopic, mineralogical, and molecular analysis of the samples, as described below. Site selection is intended to increase the chances of the Lander being finally located in a region which has relatively low concentrations of aeolian dust mounds and a high probability of underlying dense sedimentary material. Drilling and sampling is planned to a depth in the range 1 to 1.5 metres. Due to its size, and other factors, this large drill will have to be located on the main Lander. The maximum drilling depth achievable will depend on the constraints imposed by the Lander configuration on the accommodation of the multiple drill bits, as well as other resource limitations and the nature of the regolith. The actual mounting of the drill on the Lander should if possible include the possibility to adjust the position of drill entry over a limited range. Exactly how that is to be achieved will depend on the intended basic design of the Lander. Rock interior samuling is intended to provide unoxidised samples from several individual rocks within the range of a surface Rover. It is envisaged that the primary purpose of the Rover will be to obtain selected samples for in-situ detailed analysis at the Lander and, on the basis of those analyses, for a subset to be stored for return to Earth. This subset would be in addition to selected subsurface samples. Sample acquisition from several centimetres depth may follow after an initial examination below the surface rind of the rock. A surface grinder and microscope is planned for that initial task. Drilling and sample acquisition/storage could be performed by a modified version of the existing ESA Small Sample Acquisition & Distribution System. A breadboard model has been built and performance tested under - 150 ‘C/vacuum conditions. An alternative approach to rock sampling was also considered. This involved simply the collection of small (ems) sized surface ‘rocks’ by the Rover and their subsequent sectioning at the Lander, preparatory to microscopic analysis. This avoids the complications of the Rover based drilling operations, although at the cost of some biassing in the sampling process. Macroscouic surface analvsis would have two main functions. It would seek evidence of gross features in surface rock structures which may indicate previous biological activity ; at its most simple that could be the equivalent of degraded stromatolite structures. It would also be used to identify target rocks for subsequent close-up examination and for possible interior rock sampling. The equipment to perform these functions will likely be derived from that currently selected for flight on future Mars missions. INSTRUMENTATION Sample acquisition, handling, and preparation for the analysis instrumentation is the crucial yet most challenging part of the overall in-situ analysis process. ESA has funded several studies and tests of drilling systems, in connection with the Rosetta cometary mission. Sample handling has also been addressed within that

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same context. Currently, the Manned Spaceflight Directorate has initiated exobiology facility, with a major emphasis on these sampling processes.

a Phase A study on this proposed

The essence of the proposed instrumentation complement is that it forms a unified assembly designed to reduce the ambiguities which so often follow from single instrument determinations. This instrumentation has two basic components. First, the samples are observed visually after suitable preparatory treatment by sawing/grinding operations. This basic mineralogical analysis is an essential first step. It characterizes the sample and allows the possibility of observing any embedded larger fossil structures. Carefully selected samples may then be passed for spectroscopic and chemical analysis. Where there are indications of possible smaller scale fossil structures those samples can be subjected to sub-micron scale morphological analysis by the atomic force microscope. Sample Acquisition is principally by percussive core drilling and sequential core sample extraction. The main drill is for subsurface sampling, with a core diameter ~1 cm. Sampling depth is at least 1 m. The further definition of this system is on-going. Earlier studies indicated a total mass envelope of 6.5 kg for this Lander based unit. Sampling of the interior of large surface rocks below the weathered rind is to be accomplished by a percussive core drill penetrating up to 15 cm. This drill would be mounted on the Rover, together with the necessary sample storage containers. It is expected that the principal analytical facilities would be located at the Lander. The core diameter would match that of the main subsurface drill. On the basis of the Rosetta system and other studies, a total mass of 3.5 kg is expected. Sample preparation for microscopy requires the conversion of a core into a smooth surface. A hard rock sectioning system, of some 300 g mass, was proposed for the cutting/smoothing process. The analysis systems require access to grains as well as to a polished sample. A basic grinding system is therefore an integral part of the sample preparation system. Precautions obviously are needed to deal with contamination. Observational methods selected involve a macroscopic system, low and high resolution optical microscopes, and an atomic force microscope to reach the nanometre resolution level. On Earth, the earliest prokaryotic microbial ecosystems have left two main categories of morphological fossil evidence. At the macroscopic level are the laminated biosedimentary structures (stromatolites) which have been left by mat forming bacteria. These microbiolite structures have a record extending back some 3.5 Ga on Earth. If Mars had a comparable early period of abundant water, then it is possible that macroscopic microbiolite structures may be associated with the oldest of the Martian sedimentary structures, Hence, degraded macroscopic structures of similar origin might be observed in sedimentary surface rocks and scarps by a panoramic camera with a resolution of about one millimetre. The camera will also be extensively used in a geological and mineralogical context. The second main category of morphological fossil evidence left on Earth derives from the cellular relics of individual micro-organisms. These microfossils, whose record also extends back to about 3.5 Ga, are to be found ranging in size from ~5 microns for some individual bacteria through to about 1 mm for filamentous cyanobacteria. Consequently, by analogy, low power and high power optical microscopes will be required, together with an Atomic Force Microscope to reach the sub-micron resolution level. Tables 2a and 2b summarize characteristics:

the primary and secondary science objectives

of these instruments

and their basic

Analvtical Methods include radiation and particle spectroscopic techniques, together with mass discrimination instruments. Each of these may be applied to the samples derived from surface rocks and from the subsurface drilling. The resulting mineralogical and geochemical analyses, together with the petrological studies using the observational instruments, provide the essential basic information on the genera1 planetological setting of the site, the local environment, and on any traces of past or present biological activity.

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Table 2a.. Scientific objectif of the instrumentation payload

PERFORMANCE

INSTRUMENT

OTHER OBJECTIVES

EXOBIOLOGY OBJECTIVES

Panoramic Stereo

1000x1000px 0.3 mrad/px 14 Filters.

Study rock types/gross features. Rover targets

Landing site survey Direct the Rover.

Low Resol. Microscope

0.1 mm/px. 5 filters.

Examine samples prior to high resolution microscopy.

Check samples prior to them. analysis or storage.

Optical Microscope

Resol. #3Fm. Depth of field <20F

Detection of large fossil structures.

Intermediate resol. mineralogical studies.

Atomic Force Microscope

1 nanometer Field lxlF, to 5Ox50F.

Imaging of pre-selected fossils

High resolution mineralogy.

Table 2b. Main characterisitics of the instrumentation payload

INSTRUMENT

MASS (kg)

POWER (W)

DATA(Mb/d)

Panoramic Camera

2s

8

8

Low Resol. Microscope

0.2

2,5

Optical Microscope

0.3

4

3

300

Atomic Force Microscope

1.5

5

1

500

VOL. (cm3)

I 100+ mast/elec 200

Such mineralogical characterization of the site samples will comprise of the following objectives: - mineralogy, texture and bulk chemistry of primary rocks - mineralogy and sedimentology of the soil, and wind/water deposited sediments, regolith etc.(including grain size/shapes secondary minerals such as clays, carbonates, zeolites, hydrates, chlorites, etc) - mineralogy of mobile phases and hard ground cements (halogenides, sulphates, nitrates, silica, carbonates, iron oxyhydrates, etc) - search for biomarkers (framboidal sulphides or oxides, bio-phosphates, oxalates, silica, biogenic magnetite, barite, and the fossil structures, as discussed earlier) Geochemical analysis of these same samples will establish their elemental bulk composition. Major, minor and trace element abundances will help define the geological history of the site and an analysis of the oxidation state of certain elements (eg., Fe, Mn, S, N,.) will provide information on the redox conditions there and their historical development. A knowledge of the relative abundances of the biologically significant elements C, H, N, 0, S and P, and their distribution between organic and inorganic matter is of particular interest. The

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abundance of nitrogen and its oxidation state in the Martian soil will be of significance happened to the initial atmospheric nitrogen.

in determining

what

Isotope ratios can provide a very valuable set of chemical biomarkers. Most notable is the C depletion in favour of ‘*C in photosynthesis. On Earth, this depletion amounts to 20 to 30% in the average biomass when compared to that in inorganic carbon and this difference has been maintained over about 3.5 Ga. Similarly, substantial isotopic fractionation, as much as 30%,in favour of hydrogen against deuterium is found to occur through the activity of methanogenic micro-organisms on Earth. In addition a determination of “N/14N can provide important information on possible biological activity, as can the 34S/32S isotopic composition change between sulphides and sulphates The determination of minerals such as phosphates, manganese oxides, and certain carbonates which may result from biological processes, are important objectives, as is the nitrate and sulphate content. So too is the quantitative determination of water, particularly as a function of depth. The depth profile of the abundance of oxidants in the regolith is another obvious requirement. As yet no organics have been found on Mars and their discovery and analysis would be of prime importance for exobiology. It will be necessary however to carefully differentiate between organics of an abiotic origin, especially those of meteoritic origin.

Table 3. First priority instruments

for chemical analysis.

INSTRUMENT

ANALYSIS

MASS (kg)

Alpha/Proton/ X-Ray Spectrometer

Elemental analysis for all except H, and He

095

Mijssbauer Spectrometer

Fe-bearing minerals Fe-oxidation state and ratios.

0.5

Laser Raman Spectrometer 200-3500cm-’ & 8cm” resl.

Molecular analysis of organics and of minerals.

1.5

IR Spectrometer 0.8 to 10F. Spectr. Res. 100. Snatial Reso1.200F.

Molecular analysis of minerals and organics.

1.0

Pyrolytic Gas Chromat. and Mass Spectrometer

Analyse organic isotopic chirality

4.0

inorganic/ compounds; ratio and determ.

POWER (W)

(1:;k) 1.6

600

1.2 Mb/ sample

250

TBD

800

TBD

(2.~;k)

3.5

W8@4

2.5Mb max. 0.6Mb min.

On Earth, the primary biopolymers undergo a complex process of degradation and condensation following the death of the organism. The result is a complex and chemically stable macromolecular material (kerogen). In addition, certain stable lipid rich biopolymers survive this degradation process, to contribute directly to the constitution of the kerogen. Sediments may also contain stable organic compounds, especially metalloporphyrin pigments, which have survived at least in part, the processes of alteration. Many can be classified as biomarkers on the basis of their structure and/or carbon isotopic composition. Such biomarkers

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and kerogen of recognisable biological origin have been found in sediments on Earth which date back at least 0.5 Ga. It is therefore conceivable that such materials might be detected on Mars, given appropriate sites. Taking into account factors such as survivability, following priority order in searching for organics: 1. 2. 3.

especially

in an oxidising

environment,

Volatile low molecular weight compounds, including hydrocarbons (especially methane), alkanoic acids and peroxy acids including hydrocarbons (straight and branched chain, Medium molecular weight compounds, isoprenoids, terpenoids, steroids, and aromatics). Macromolecular components, which would be kerogen-like components, oligo- and polypeptides.

Table 3 lists the analysis determinations, elemental, CONCLUSIONS

instruments which have been identified isotopic, and molecular, outlined above:

: A POSSIBLE CONFIGURATION

as suitable,

AND OPERATING

in total, to cover the range of

ARRANGEMENT

The precise arrangement of the instrumentation and indeed, the total complement actually be accommodated will obviously finally depend upon the characteristics spacecraft designs. The following gives an indication of what might be accommodated On

has led to the

of instruments that can of the mission and the :

the Rover. either (i)

-

robotic positioning arm a rock surface grinder low power microscope APX spectrometer a small rock coring drill, core sample containers

(2.0 (0.4 (0.2 (0.5 (3.5

kg) kg) kg) kg) kg)

Total mass or (ii)

- small robotic arm equipped to collect ems sized surface rocks, place in transfer containers, and subsequently pass to the Lander (2.0 kg) - colour microscope camera (0.2 kg) - sample containers for the collected small rock samples. (0.5 kg)

On the Lander: - the subsurface drill system - sample handling/distribution - sample sectioning - sample grinding - low resolution microscope - optical microscope - Atomic Force Microscope - microscopy transfer stage - Alpha/Proton/X-Ray spectrometer - Mijssbauer spectrometer - Laser Raman Spectrometer - IR Microspectrometer - Pyrolytic,Gas Chromatograph,Mass Spec. - Oxidant detector - Laser ablation ICP mass spectrometer

(,:.:, 2; (0:3 kg) (0.4 kg) (0.2 kg) (0.3 kg) (1.5 kg) (1.0 kg) (0.5 kg) (0.5 kg) (1.5 kg) (1.0 kg) (5.5 kg) (0.4 kg)

The Lander is considered as the centre for subsurface sampling and for the in situ sample preparation and analysis processes. The Rover then provides a selection of rock samples from nearby locations either as small core samples or as small (ems) rocks, for sawing in the Lander.

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ACKNOWLEDGMENTS This work was undertaken on the initiative of the Manned Spaceflight and Microgravity Directorate of the European Space Agency. During the development of this study, we have been greatly assisted by the following advisors : Nathalie Cabrol, Ignasi Casanova, Howell Edwards, Michael Femandes, G&tar Klingelhdfer, Jens Knudsen, Alexandra MacDermott, Wojtek Markiewick, Dave Rothery, Manfred Schidlowski, Robert Stemberg, Harald Strauss. We would like also to thank the following ESA personnel for their contributioins and assistance : Augustin Chicarro, Pierre Coste, Elena Grifoni, Gerhard Kminek, Franc0 Ongaro, Peter Schiller and Gunther Seibert. REFERENCES Brack, A., P. Forterre, G. Horneck, C. Pillinger, M. Schidlowski and H. Wlnke, ESA Exobiology Science Team Stu& on the Search for Life in the Solar System, Final Report, Fitton B. (Ed.), (1997). Brack, A., B. Hofmann, G. Homeck, G. Kurat, J. Maxwell, G. Ori, C. Pillinger, F. Raulin, N. Thomas, F. Westall, ESA Exobiology Science Team Study on the Search for Life on Mars, Final Report, Fitton B. (Ed.), (1998).