Preservation of martian organic and environmental records: final report of the Mars biosignature working group

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars. Orbital images confirm that layered rocks achieved kilometer-scale thicknesses in some regions of ancient Mars. Clearly, interplays of sedimentation and erosional processes govern present-day exposures, and our understanding of these processes is incomplete. MSL can document and evaluate patterns of stratigraphic development as well as the sources of layered materials and their subsequent diagenesis. It can also document other potential biosignature repositories such as hydrothermal environments. These capabilities offer an unprecedented opportunity to decipher key aspects of the environmental evolution of Mars' early surface and aspects of the diagenetic processes that have operated since that time. Considering the MSL instrument payload package, we identified the following classes of biosignatures as within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.     

The Urey instrument: an advanced in situ organic and oxidant detector for Mars exploration

The Urey organic and oxidant detector consists of a suite of instruments designed to search for several classes of organic molecules in the martian regolith and ascertain whether these compounds were produced by biotic or abiotic processes using chirality measurements. These experiments will also determine the chemical stability of organic molecules within the host regolith based on the presence and chemical reactivity of surface and atmospheric oxidants. Urey has been selected for the Pasteur payload on the European Space Agency's (ESA's) upcoming 2013 ExoMars rover mission. The diverse and effective capabilities of Urey make it an integral part of the payload and will help to achieve a large portion of the mission's primary scientific objective: "to search for signs of past and present life on Mars." This instrument is named in honor of Harold Urey for his seminal contributions to the fields of cosmochemistry and the origin of life.     

The biological terraforming of Mars: planetary ecosynthesis as ecological succession on a global scale

Mars is bitterly cold and dry, but robotic spacecraft have returned abundant data that indicate Mars once had a much warmer and wetter climate in the past. These data, the basis of the search for past or present life on Mars, suggest the possibility of returning Mars to its previous climate by global engineering techniques. Greenhouse gases, such as perfluorocarbons, appear to be the best method for warming Mars and increasing its atmospheric density so that liquid water becomes stable. The process of making Mars habitable for terrestrial organisms is called terraforming or planetary ecosynthesis. The process of introducing terrestrial ecosystems to Mars can be compared with a descent down a high mountain. Each drop in elevation results in a warmer, wetter climate and more diverse biological community. Beginning with a polar desert, the sequence of ecosystems passes through tundra, boreal forest, and temperate ecosystems where moisture determines the presence of desert, grassland, or forest. This model suggests a sequence for the introduction of ecosystems to Mars and the communities to search for potential colonizing species for Mars.     

好奇心号巡视器及其特点分析

"火星科学实验室"(Mars Science Laboratory,MSL)是NASA于2011年11月26日发射的火星探测器,其上的好奇心号(Curiosity)巡视器已经于2012年8月6日着陆火星;其主要科学目标包括研究火星存在生命的可能性、火星气候特征、火星地质过程,并为将来的载人着陆作准备;经过多次论证,其着陆区为盖尔撞击坑(Gale Crater)。与过去的火星巡视器相比,它携带了更加先进的科学仪器,能够精确分析采集样品的化学成分、光谱特征等;在科学工作小组的指导下,其运行模式包括行走、勘查、接近目标、接触目标与样品分析;通过上述工作,"火星科学实验室"将对火星生命及可居住性进行全面探测。     

Astrobiology through the ages of Mars: the study of terrestrial analogues to understand the habitability of Mars

Mars has undergone three main climatic stages throughout its geological history, beginning with a water-rich epoch, followed by a cold and semi-arid era, and transitioning into present-day arid and very cold desert conditions. These global climatic eras also represent three different stages of planetary habitability: an early, potentially habitable stage when the basic requisites for life as we know it were present (liquid water and energy); an intermediate extreme stage, when liquid solutions became scarce or very challenging for life; and the most recent stage during which conditions on the surface have been largely uninhabitable, except perhaps in some isolated niches. Our understanding of the evolution of Mars is now sufficient to assign specific terrestrial environments to each of these periods. Through the study of Mars terrestrial analogues, we have assessed and constrained the habitability conditions for each of these stages, the geochemistry of the surface, and the likelihood for the preservation of organic and inorganic biosignatures. The study of these analog environments provides important information to better understand past and current mission results as well as to support the design and selection of instruments and the planning for future exploratory missions to Mars.     

火星精确着陆制导问题分析与展望

美国火星科学实验室(MSL)任务成功将“好奇”号火星车着陆到火星表面,开创了火星精确着陆探测的新局面。以MSL着陆任务为典型代表,分析了目前火星着陆探测进入、下降和着陆（Entry, Descent and Landing, EDL）过程的制导方案及制导系统的发展趋势。以在火星高海拔、复杂地形区域定点着陆为潜在工程目标,归纳了火星EDL过程面临的制导主要问题。根据未来制导系统自主性和自适应性的技术需求及潜在工程任务制导面临的问题,提出了火星EDL制导方面需要解决的关键技术,并对其在未来工程中的应用潜力进行了展望。     

The Mawrth Vallis region of Mars: A potential landing site for the Mars Science Laboratory (MSL) mission

The primary objective of NASA's Mars Science Laboratory (MSL) mission, which will launch in 2011, is to characterize the habitability of a site on Mars through detailed analyses of the composition and geological context of surface materials. Within the framework of established mission goals, we have evaluated the value of a possible landing site in the Mawrth Vallis region of Mars that is targeted directly on some of the most geologically and astrobiologically enticing materials in the Solar System. The area around Mawrth Vallis contains a vast (>1?×?10? km2) deposit of phyllosilicate-rich, ancient, layered rocks. A thick (>150?m) stratigraphic section that exhibits spectral evidence for nontronite, montmorillonite, amorphous silica, kaolinite, saponite, other smectite clay minerals, ferrous mica, and sulfate minerals indicates a rich geological history that may have included multiple aqueous environments. Because phyllosilicates are strong indicators of ancient aqueous activity, and the preservation potential of biosignatures within sedimentary clay deposits is high, martian phyllosilicate deposits are desirable astrobiological targets. The proposed MSL landing site at Mawrth Vallis is located directly on the largest and most phyllosilicate-rich deposit on Mars and is therefore an excellent place to explore for evidence of life or habitability.     

Vanguard--a European robotic astrobiology-focussed Mars sub-surface mission proposal

We present a new European Mars mission proposal to build on the UK-led Beagle2 Mars mission and continue its astrobiology-focussed investigation of Mars. The small surface element to be delivered to the Martian surface--Vanguard--is designed to be carried by a Mars Express-type spacecraft bus to Mars and adopts a similar entry, descent and landing system as Beagle2. The surface element comprises a triad of robotic devices--a lander, a micro-rover of the Sojourner class for surface mobility, and three ground-penetrating moles mounted onto the rover for sub-surface penetration to 5 m depth. The major onboard instruments on the rover include a Raman spectrometer/imager, a laser plasma spectrometer, an infrared spectrometer--these laser instruments provide the basis for in situ "remote" sensing of the sub-surface Martian environment within a powerful scientific package. The moles carry the instruments' sensor head array to the sub-surface. The moles are thus required to undergo a one-way trip down the boreholes without the need for recovery of moles or samples, eliminating much of the robotic complexity invoked by such operations.     

Bacterial growth at the high concentrations of magnesium sulfate found in martian soils

The martian surface environment exhibits extremes of salinity, temperature, desiccation, and radiation that would make it difficult for terrestrial microbes to survive. Recent evidence suggests that martian soils contain high concentrations of MgSO? minerals. Through warming of the soils, meltwater derived from subterranean ice-rich regolith may exist for an extended period of time and thus allow the propagation of terrestrial microbes and create significant bioburden at the near surface of Mars. The current report demonstrates that halotolerant bacteria from the Great Salt Plains (GSP) of Oklahoma are capable of growing at high concentrations of MgSO? in the form of 2 M solutions of epsomite. The epsotolerance of isolates in the GSP bacterial collection was determined, with 35% growing at 2 M MgSO?. There was a complex physiological response to mixtures of MgSO? and NaCl coupled with other environmental stressors. Growth also was measured at 1 M concentrations of other magnesium and sulfate salts. The complex responses may be partially explained by the pattern of chaotropicity observed for high-salt solutions as measured by agar gelation temperature. Select isolates could grow at the high salt concentrations and low temperatures found on Mars. Survival during repetitive freeze-thaw or drying-rewetting cycles was used as other measures of potential success on the martian surface. Our results indicate that terrestrial microbes might survive under the high-salt, low-temperature, anaerobic conditions on Mars and present significant potential for forward contamination. Stringent planetary protection requirements are needed for future life-detection missions to Mars.     

A concept for NASA's Mars 2016 astrobiology field laboratory

The Mars Program Plan includes an integrated and coordinated set of future candidate missions and investigations that meet fundamental science objectives of NASA and the Mars Exploration Program (MEP). At the time this paper was written, these possible future missions are planned in a manner consistent with a projected budget profile for the Mars Program in the next decade (2007-2016). As with all future missions, the funding profile depends on a number of factors that include the exact cost of each mission as well as potential changes to the overall NASA budget. In the current version of the Mars Program Plan, the Astrobiology Field Laboratory (AFL) exists as a candidate project to determine whether there were (or are) habitable zones and life, and how the development of these zones may be related to the overall evolution of the planet. The AFL concept is a surface exploration mission equipped with a major in situ laboratory capable of making significant advancements toward the Mars Program's life-related scientific goals and the overarching Vision for Space Exploration. We have developed several concepts for the AFL that fit within known budget and engineering constraints projected for the 2016 and 2018 Mars mission launch opportunities. The AFL mission architecture proposed here assumes maximum heritage from the 2009 Mars Science Laboratory (MSL). Candidate payload elements for this concept were identified from a set of recommendations put forth by the Astrobiology Field Laboratory Science Steering Group (AFL SSG) in 2004, for the express purpose of identifying overall rover mass and power requirements for such a mission. The conceptual payload includes a Precision Sample Handling and Processing System that would replace and augment the functionality and capabilities provided by the Sample Acquisition Sample Processing and Handling system that is currently part of the 2009 MSL platform.     

The Dynamic Albedo of Neutrons (DAN) experiment for NASA's 2009 Mars Science Laboratory

We present a summary of the physical principles and design of the Dynamic Albedo of Neutrons (DAN) instrument onboard NASA's 2009 Mars Science Laboratory (MSL) mission. The DAN instrument will use the method of neutron-neutron activation analysis in a space application to study the abundance and depth distribution of water in the martian subsurface along the path of the MSL rover.     

美国火星表面探测使命述评（上）

从1975年发射（1976年着陆火星）的海盗-1探测器以来,美国已成功执行了6次火星表面探测使命,即海盗-1与海盗-2轨道器/着陆器,＂火星探路者＂（MPF）着陆器/巡游车,＂勇气＂与＂机遇＂火星探测巡游车（MER）,以及＂凤凰＂着陆器;而推迟到2011年发射的＂好奇心＂火星科学实验室（MSL）将火星着陆技术与表面巡游车技术推向一个新的高度。从＂海盗＂着陆器到＂好奇心＂巡游车、美国历经三种火星着陆系统与三代火星表面巡游车技术的发展。三种着陆系统为着陆腿着陆系统（＂海盗＂与＂凤凰＂）,气囊着陆系统（MPF与MER）,以及空中吊机着陆系统（MSL）。三代巡游车为MPF＂旅居者＂巡游车、MER＂勇气＂与＂机遇＂巡游车,以及MSL＂好奇心＂巡游车。现在,美国在火星进入、降落与着陆（EDL）运作与表面避障移动方面,已达到技术成熟与先进的水平,满足安全着陆与表面移动探测的要求。文章阐述美国上述七项火星表面探测使命的立项背景、科学目标与有效载荷、飞行系统组成,以及飞行运作程序;分析美国火星着陆技术与表面巡游车技术的发展。     

美国火星表面探测使命述评（下）

从1975年8月发射（1976年7月着陆火星）的海盗-1探测器以来,美国已成功执行了6次火星表面探测使命,即海盗-1与海盗-2轨道器/着陆器,＂火星探路者＂（MPF）着陆器/巡游车,＂勇气＂与＂机遇＂火星探测巡游车（MER）,以及＂凤凰＂着陆器;而推迟到2011年发射的火星科学实验室（MSL）将火星着陆技术与表面巡游车技术推向一个新的高度。从＂海盗＂着陆器到MSL＂好奇心＂巡游车、美国历经三种火星着陆系统与三代火星表面巡游车技术的发展。三种着陆系统为着陆腿着陆系统（＂海盗＂与＂凤凰＂）,气囊着陆系统（MPF与MER）,以及空中吊机着陆系统（MSL）。三代巡游车为MPF＂旅居者＂巡游车、MER＂勇气＂与＂机遇＂巡游车,以及MSL＂好奇心＂巡游车。现在,美国在火星进入、降落与着陆（EDL）运作与表面避障移动方面,已达到技术成熟与先进的水平,满足安全着陆与表面移动探测的要求。文章阐述美国上述七项火星表面探测使命的立项背景、科学目标与有效载荷、飞行系统组成,以及飞行运作程序;分析美国火星着陆技术与表面巡游车技术的发展。     

An extensive phase space for the potential martian biosphere

We present a comprehensive model of martian pressure-temperature (P-T) phase space and compare it with that of Earth. Martian P-T conditions compatible with liquid water extend to a depth of ～310?km. We use our phase space model of Mars and of terrestrial life to estimate the depths and extent of the water on Mars that is habitable for terrestrial life. We find an extensive overlap between inhabited terrestrial phase space and martian phase space. The lower martian surface temperatures and shallower martian geotherm suggest that, if there is a hot deep biosphere on Mars, it could extend 7 times deeper than the ～5?km depth of the hot deep terrestrial biosphere in the crust inhabited by hyperthermophilic chemolithotrophs. This corresponds to ～3.2% of the volume of present-day Mars being potentially habitable for terrestrial-like life.     

Survival of methanogens during desiccation: implications for life on Mars

The relatively recent discoveries that liquid water likely existed on the surface of past Mars and that methane currently exists in the martian atmosphere have fueled the possibility of extant or extinct life on Mars. One possible explanation for the existence of the methane would be the presence of methanogens in the subsurface. Methanogens are microorganisms in the domain Archaea that can metabolize molecular hydrogen as an energy source and carbon dioxide as a carbon source and produce methane. One factor of importance is the arid nature of Mars, at least at the surface. If one is to assume that life exists below the surface, then based on the only example of life that we know, liquid water must be present. Realistically, however, that liquid water may be seasonal just as it is at some locations on our home planet. Here we report on research designed to determine how long certain species of methanogens can survive desiccation on a Mars soil simulant, JSC Mars-1. Methanogenic cells were grown on JSC Mars-1, transferred to a desiccator within a Coy anaerobic environmental chamber, and maintained there for varying time periods. Following removal from the desiccator and rehydration, gas chromatographic measurements of methane indicated survival for varying time periods. Methanosarcina barkeri survived desiccation for 10 days, while Methanobacterium formicicum and Methanothermobacter wolfeii were able to survive for 25 days.     

Identification of morphological biosignatures in Martian analogue field specimens using in situ planetary instrumentation

We have investigated how morphological biosignatures (i.e., features related to life) might be identified with an array of viable instruments within the framework of robotic planetary surface operations at Mars. This is the first time such an integrated lab-based study has been conducted that incorporates space-qualified instrumentation designed for combined in situ imaging, analysis, and geotechnics (sampling). Specimens were selected on the basis of feature morphology, scale, and analogy to Mars rocks. Two types of morphological criteria were considered: potential signatures of extinct life (fossilized microbial filaments) and of extant life (crypto-chasmoendolithic microorganisms). The materials originated from a variety of topical martian analogue localities on Earth, including impact craters, high-latitude deserts, and hydrothermal deposits. Our in situ payload included a stereo camera, microscope, M?ssbauer spectrometer, and sampling device (all space-qualified units from Beagle 2), and an array of commercial instruments, including a multi-spectral imager, an X-ray spectrometer (calibrated to the Beagle 2 instrument), a micro-Raman spectrometer, and a bespoke (custom-designed) X-ray diffractometer. All experiments were conducted within the engineering constraints of in situ operations to generate realistic data and address the practical challenges of measurement. Our results demonstrate the importance of an integrated approach for this type of work. Each technique made a proportionate contribution to the overall effectiveness of our "pseudopayload" for biogenic assessment of samples yet highlighted a number of limitations of current space instrument technology for in situ astrobiology.     

Mars through the looking glass: an interdisciplinary analysis of forward and backward contamination

The exploration of the planet Mars represents a significant milestone in humanity's exploration of the Universe. In the quest to better explore and understand Mars, issues of forward and backward contamination are particularly pertinent. This paper provides an interdisciplinary analysis of forward and backward contamination. Its substantive material reflects the scientific and technical concerns through the looking glass of legal and policy issues, and vice versa. The paper critically surveys contamination issues of current, nascent and proposed Mars missions from a scientific viewpoint. It then makes a comparative review of legal and policy mechanisms designed to protect against such contamination. It draws cross-linkages between the sciences and the law in this area. The paper then delineates a suggested interdisciplinary framework to protect against forward and backward contamination. This framework is based on co-operation between the various nations undertaking Mars missions, as well as between the various fields of expertise. It highlights the importance of an interdisciplinary overview in the implementation of measures protecting against forward and backward contamination. Strategies on the implementation of these measures are also outlined.     

Terraforming Mars: conceptual solutions to the problem of plant growth in low concentrations of oxygen

The widespread growth of higher plants on Mars following ecopoiesis has often been invoked as a method of generating atmospheric oxygen. However, one issue that has been overlooked in this regard is the fact that terrestrial plants do not thrive under conditions of low oxygen tension. A review of the relevant botanical literature reveals that the high oxygen demands of root respiration could limit the introduction of most plants on Mars until after terraforming has raised the atmospheric pO2 to 20-100 mbar. A variety of physiological strategies are discussed which, if it is possible to implement them in a genetically engineered plant specifically designed for life on Mars, might allow this problem to be overcome.     

Biological potential of Martian hydrothermal systems

A source of energy to power metabolism may be a limiting factor in the abundance and spatial distribution of past or extant life on Mars. Although a global average of chemical energy available for microbial metabolism and biomass production on Mars has been estimated previously, issues of how the energy is distributed and which particular environments have the greatest potential to support life remain unresolved. We address these issues using geochemical models to evaluate the amounts of chemical energy available in one potential biological environment, Martian hydrothermal systems. In these models, host rock compositions are based upon the compositions of Martian meteorites, which are reacted at high temperature with one of three groundwater compositions. For each model, the values for Gibbs energy of reactions that are important for terrestrial chemosynthetic organisms and likely representative for putative Martian microbes are calculated. Our results indicate that substantial amounts of chemical energy may be available in these systems, depending most sensitively upon the composition of the host rock. From the standpoint of sources of metabolic energy, it is likely that suitable environments exist to support Martian life.     

Survival of Bacillus subtilis endospores on ultraviolet-irradiated rover wheels and Mars regolith under simulated Martian conditions

Endospores of Bacillus subtilis HA101 were applied to a simulated Mars Exploration Rover (MER) wheel and exposed to Mars-normal UV irradiation for 1, 3, or 6 h. The experiment was designed to simulate a contaminated rover wheel sitting on its landing platform before rolling off onto the martian terrain, as was encountered during the Spirit and Opportunity missions. When exposed to 1 h of Mars UV, a reduction of 81% of viable endospores was observed compared to the non-UV irradiated controls. When exposed for 3 or 6 h, reductions of 94.6% and 96.6%, respectively, were observed compared to controls. In a second experiment, the contaminated rover wheel was rolled over a bed of heat-sterilized Mars analog soil; then the analog soil was exposed to full martian conditions of UV irradiation, low pressure (6.9 mbar), low temperature (-10°C), and an anaerobic CO(2) martian atmosphere for 24 h to determine whether endospores of B. subtilis on the contaminated rover wheel could be transferred to the surface of the analog soil and survive martian conditions. The experiment simulated conditions in which a rover wheel might come into contact with martian regolith immediately after landing, such as is designed for the upcoming Mars Science Laboratory (MSL) rover. The contaminated rover wheel transferred viable endospores of B. subtilis to the Mars analog soil, as demonstrated by 31.7% of samples showing positive growth. However, when contaminated soil samples were exposed to full martian conditions for 24 h, only 16.7% of samples exhibited positive growth-a 50% reduction in the number of soil samples positive for the transferred viable endospores.