Review of wet environment types on Mars with focus on duration and volumetric issues

The astrobiological significance of certain environment types on Mars strongly depends on the temperature, duration, and chemistry of liquid water that was present there in the past. Recent works have focused on the identification of signs of ancient water on Mars, as it is more difficult to estimate the above-mentioned parameters. In this paper, two important factors are reviewed, the duration and the volume of water at different environment types on past and present Mars. Using currently available information, we can only roughly estimate these values, but as environment types show characteristic differences in this respect, it is worth comparing them and the result may have importance for research in astrobiology. Impact-induced and geothermal hydrothermal systems, lakes, and valley networks were in existence on Mars over the course of from 10(2) to 10(6) years, although they would have experienced substantially different temperature regimes. Ancient oceans, as well as water in outflow channels and gullies, and at the microscopic scale as interfacial water layers, would have had inherently different times of duration and overall volume: oceans may have endured from 10(4) to 10(6) years, while interfacial water would have had the smallest volume and residence time of liquid phase on Mars. Martian wet environments with longer residence times of liquid water are believed to have existed for that amount of time necessary for life to develop on Earth between the Late Heavy Bombardment and the age of the earliest fossil record. The results of this review show the necessity for more detailed analysis of conditions within geothermal heat-induced systems to reconstruct the conditions during weathering and mineral alteration, as well as to search for signs of reoccurring wet periods in ancient crater lakes.     

Location and sampling of aqueous and hydrothermal deposits in martian impact craters

Do large craters on Mars represent sites that contain aqueous and hydrothermal deposits that provide clues to astrobiological processes? Are these materials available for sampling in large craters? Several lines of evidence strongly support the exploration of large impact craters to study deposits important for astrobiology. The great depth of impact craters, up to several kilometers relative to the surrounding terrain, can allow the breaching of local aquifers, providing a source of water for lakes and hydrothermal systems. Craters can also be filled with water from outflow channels and valley networks to form large lakes with accompanying sedimentation. Impact melt and uplifted basement heat sources in craters > 50 km in diameter should be sufficient to drive substantial hydrothermal activity and keep crater lakes from freezing for thousands of years, even under cold climatic conditions. Fluid flow in hydrothermal systems is focused at the edges of large planar impact melt sheets, suggesting that the edge of the melt sheets will have experienced substantial hydrothermal alteration and mineral deposition. Hydrothermal deposits, fine-grained lacustrine sediments, and playa evaporite deposits may preserve evidence for biogeochemical processes that occurred in the aquifers and craters. Therefore, large craters may represent giant Petri dishes for culturing preexisting life on Mars and promoting biogeochemical processes. Landing sites must be identified in craters where access to the buried lacustrine sediments and impact melt deposits is provided by processes such as erosion from outflow channels, faulting, aeolian erosion, or excavation by later superimposed cratering events. Very recent gully formation and small impacts within craters may allow surface sampling of organic materials exposed only recently to the harsh oxidizing surface environment.     

Brines in seepage channels as eluants for subsurface relict biomolecules on Mars?

Water, vital for life, not only maintains the integrity of structural and metabolic biomolecules, it also transports them in solution or colloidal suspension. Any flow of water through a dormant or fossilized microbial community elutes molecules that are potentially recognizable as biomarkers. We hypothesize that the surface seepage channels emanating from crater walls and cliffs in Mars Orbiter Camera images results from fluvial erosion of the regolith as low-temperature hypersaline brines. We propose that, if such flows passed through extensive subsurface catchments containing buried and fossilized remains of microbial communities from the wet Hesperian period of early Mars (approximately 3.5 Ga ago), they would have eluted and concentrated relict biomolecules and delivered them to the surface. Life-supporting low-temperature hypersaline brines in Antarctic desert habitats provide a terrestrial analog for such a scenario. As in the Antarctic, salts would likely have accumulated in water-filled depressions on Mars by seasonal influx and evaporation. Liquid water in the Antarctic cold desert analogs occurs at -80 degrees C in the interstices of shallow hypersaline soils and at -50 degrees C in salt-saturated ponds. Similarly, hypersaline brines on Mars could have freezing points depressed below -50 degrees C. The presence of hypersaline brines on Mars would have extended the amount of time during which life might have evolved. Phototrophic communities are especially important for the search for life because the distinctive structures and longevity of their pigments make excellent biomarkers. The surface seepage channels are therefore not only of geomorphological significance, but also provide potential repositories for biomolecules that could be accessed by landers.     

火星稀薄大气参数对进入器气动特性的影响

针对火星稀薄大气环境的不确定性对进入器气动特性的影响问题,先以海盗号火星进入器的飞行试验数据对发展的三维并行直接模拟蒙特卡罗(DSMC)仿真软件进行了算例校验,再以火星科学实验室外形为例,计算气体组分、密度、温度及速度等来流参数的不确定性对进入器气动特性的影响偏差,定性定量给出火星高空稀薄环境下大气不确定性所带来的气动力特性规律。研究结果表明,通过与海盗号飞行实验数据的对比校验了所建立方法的正确性与可靠性;CO2大气环境对进入器气动特性的影响较大,利用空气稀薄环境中的计算及实验结果亦需进行CO2效应修正,这一点与连续流区的结论一致;来流密度及速度的不确定性对气动力、力矩特性均有影响,而来流温度影响的最大偏差小于0.5%;纵向压心对来流密度、温度及速度的扰动均不敏感。     

火星液氧/甲烷推进剂原位制备技术研究进展

火星是人类深空探测的重要目标之一。利用火星上的大气、水等资源原位制备液氧、甲烷等推进剂,不仅为火星探测器返回地球、开展长周期火星探测等提供能源,也为人类建立火星生命保障系统提供必要的物质基础。分析了火星推进剂原位制备的重要性,对推进剂原位制备的资源、技术方案进行了对比分析,并重点叙述了CO_2捕集、水资源获取等方面的研究进展,以期为该领域相关研究提供参考。     

火星探测用金属/CO2燃烧技术研究进展与展望

火星原位资源利用指利用火星当地资源生产火星探测所需原料和能源,减少任务载荷,降低发射成本,是火星探测不可或缺的关键技术。金属和二氧化碳是火星重要的原位资源,部分金属可以在二氧化碳气氛中燃烧,使得金属/CO_2燃烧体系在火星上扮演地球上化石燃料/空气燃烧体系的角色成为可能。从拓展金属/CO_2燃烧技术在火星探测中应用的角度出发,梳理了火星二氧化碳收集方式、火星矿物分布和冶炼、金属/CO_2燃烧技术的主要应用方式(Mg/CO_2火箭发动机和Mg/CO_2金属燃烧器)的研究进展,并对今后的研究进行了展望。     

Geologic field work on Mars: Distance and time issues during surface exploration

Based on field experience at Analogue stations MDRS and FMARS and additional theoretical computations, motorized field work traverses were planned for various surface feature types on Mars, with emphasis on their horizontal dimension, maximal slope angle and cumulative vertical surface undulation or roughness. The aim was to explore the possibilities and characteristics of field work for different terrain types. Those terrain types are reviewed in the present study that have already been analyzed based on remote sensing data, and that are described in the scientific literature.Dunes, gullies, slope streaks, cross sections of valley networks and of lava channels might be analyzed during only one extra vehicular activity (EVA, e.g., pedestrian and vehicular field work) with the objective of a first in-situ exploration along an optimized traverse, in order to provide the most valuable scientific information on their general characteristics and origin. Smaller tectonic faults, lava flows, lobate debris aprons and outcrops of polar layered deposits can be analyzed only by several EVAs together. Analysis of large landslides, calderas and interior layered deposits produce even more difficulties on Mars, and require specialized technology. In cases where several EVAs are necessary for detailed analysis along the best traverse, mobile pressurized vehicles (with pressurized cabin for astronauts without spacesuits) or other methods would be necessary.Many of the geologic structures that have been analyzed only with remotely sensed data could not be surveyed during one field campaign, and in some cases because of high slope angle and large cumulative topographic undulation, their in-situ exploration could not be accomplished with the technological capabilities available, and in-situ analysis requires more advanced technology than long distance rovers can provide now. Hence, the prior location of important sites and the usage of robotic help will be of high importance.     

Following the kinetics: iron-oxidizing microbial mats in cold icelandic volcanic habitats and their rock-associated carbonaceous signature

Icelandic streams with mean annual temperatures of less than 5 °C, which receive the cationic products of basaltic rock weathering, were found to host mats of iron-cycling microorganisms. We investigated two representative sites. Iron-oxidizing Gallionella and iron-reducing Geobacter species were present. The mats host a high bacterial diversity as determined by culture-independent methods. β-Proteobacteria, Actinobacteria, α-Proteobacteria, and Bacteroidetes were abundant microbial taxa. The mat contained a high number of phototroph sequences. The carbon compounds in the mat displayed broad G and D bands with Raman spectroscopy. This signature becomes incorporated into the weathered oxidized surface layer of the basaltic rocks and was observed on rocks that no longer host mats. The presence of iron-oxidizing taxa in the stream microbial mats, and the lack of them in previously studied volcanic rocks in Iceland that have intermittently been exposed to surface water flows, can be explained by the kinetic limitations to the extraction of reduced iron from rocks. This type of ecosystem illustrates key factors that control the distribution of chemolithotrophs in cold volcanic environments. The data show that one promising sample type for which the hypothesis of the existence of past life on Mars can be tested is the surface of volcanic rocks that, previously, were situated within channels carved by flowing water. Our results also show that the carbonaceous signatures of life, if life had occurred, could be found in or on these rocks.     

On laboratory simulation and the effect of small temperature oscillations about the freezing point and ice formation on the evaporation rate of water on Mars

We report measurements of the evaporation rate of water under Mars-like conditions (CO2 atmosphere at 7 mbar and approximately 0 degrees C) in which small temperature oscillations about the freezing point repeatedly formed and removed a thin layer of ice. We found that the average evaporation at 2.7 +/- 0.5 degrees C without an ice layer (corrected for the difference in gravity on Earth and on Mars) was 1.24 +/- 0.12 mm/h, while at -2.1 +/- 0.3 degrees C with an ice layer the average evaporation rate was 0.84 +/- 0.08 mm/h. These values are in good agreement with those calculated for the evaporation of liquid water and ice when it is assumed that evaporation only depends on diffusion and buoyancy. Our findings suggest that such differences in evaporation rates are entirely due to the temperature difference and that the ice layer has little effect on evaporation rate. We infer that the formation of thin layers of ice on pools of water on Mars does not significantly increase the stability of water on the surface of Mars.     

Volcano-ice interaction as a microbial habitat on Earth and Mars

Volcano-ice interaction has been a widespread geological process on Earth that continues to occur to the present day. The interaction between volcanic activity and ice can generate substantial quantities of liquid water, together with steep thermal and geochemical gradients typical of hydrothermal systems. Environments available for microbial colonization within glaciovolcanic systems are wide-ranging and include the basaltic lava edifice, subglacial caldera meltwater lakes, glacier caves, and subsurface hydrothermal systems. There is widespread evidence of putative volcano-ice interaction on Mars throughout its history and at a range of latitudes. Therefore, it is possible that life on Mars may have exploited these habitats, much in the same way as has been observed on Earth. The sedimentary and mineralogical deposits resulting from volcano-ice interaction have the potential to preserve evidence of any indigenous microbial populations. These include j?kulhlaup (subglacial outflow) sedimentary deposits, hydrothermal mineral deposits, basaltic lava flows, and subglacial lacustrine deposits. Here, we briefly review the evidence for volcano-ice interactions on Mars and discuss the geomicrobiology of volcano-ice habitats on Earth. In addition, we explore the potential for the detection of these environments on Mars and any biosignatures these deposits may contain.     

Special regions in Mars exploration: Problems and potential

“Special regions” on Mars are areas designated in the COSPAR planetary protection policy as areas that may support Earth microbes inadvertently introduced to Mars, or that may have a high probability of supporting indigenous martian life. Since absolutely nothing is known about martian life, the operational definition of a special region is a place that may allow the formation and maintenance of liquid water, on or under the surface of Mars. This paper will review the special-regions concept, the implications of recent recommendations on avoiding them, and the work of the Mars science community in providing an operational definition of those areas on Mars that are “non-special.”     

The photochemical stability of carbonates on Mars

Carbonates, predominately MgCO3, have been spectroscopically identified at a level of 2-5% in martian dust. However, in spite of this observation, and a large number of climate studies that suggest 1 to several bars of CO2 should be sequestered in carbonate rocks, no outcrop-scale exposures of carbonate have been detected anywhere on Mars to date. To address one hypothesis for this long-standing puzzle, the effect of ultraviolet (UV) light on the stability of calcium carbonate in a simulated martian atmosphere was experimentally investigated. Using 13C-labeled calcite, we found no experimental evidence of the UV photodecomposition of calcium carbonate in a simulated martian atmosphere. Extrapolating the lower limit of detection of our experimental system to an upper limit of carbonate decomposition on Mars yields a quantum efficiency of 3.5 x 10(-8) molecules/photon over the wavelength interval of 190-390 nm and a maximum UV photodecomposition rate of 1.2 x 10(-13) kg m(-2) s(-1) from a calcite surface. The maximum loss of bulk calcite due to this process would be 2.5 nm year(-1) (Mars year). However, calcite is expected to be thermodynamically stable on the surface of Mars, and potential UV photodecomposition reaction mechanisms indicate that, though calcium carbonate may decompose under vacuum, it would be stable in a CO2 atmosphere. Given the expected stability of carbonate on Mars and our inability to detect carbonate decomposition, we conclude that it is unlikely that the apparent absence of extensive carbonate deposits on the martian surface is due to UV photodecomposition in the current environment.     

Giant polygons and mounds in the lowlands of Mars: signatures of an ancient ocean?

This paper presents the hypothesis that the well-known giant polygons and bright mounds of the martian lowlands may be related to a common process-a process of fluid expulsion that results from burial of fine-grained sediments beneath a body of water. Specifically, we hypothesize that giant polygons and mounds in Chryse and Acidalia Planitiae are analogous to kilometer-scale polygons and mud volcanoes in terrestrial, marine basins and that the co-occurrence of masses of these features in Chryse and Acidalia may be the signature of sedimentary processes in an ancient martian ocean. We base this hypothesis on recent data from both Earth and Mars. On Earth, 3-D seismic data illustrate kilometer-scale polygons that may be analogous to the giant polygons on Mars. The terrestrial polygons form in fine-grained sediments that have been deposited and buried in passive-margin, marine settings. These polygons are thought to result from compaction/dewatering, and they are commonly associated with fluid expulsion features, such as mud volcanoes. On Mars, in Chryse and Acidalia Planitiae, orbital data demonstrate that giant polygons and mounds have overlapping spatial distributions. There, each set of features occurs within a geological setting that is seemingly analogous to that of the terrestrial, kilometer-scale polygons (broad basin of deposition, predicted fine-grained sediments, and lack of significant horizontal stress). Regionally, the martian polygons and mounds both show a correlation to elevation, as if their formation were related to past water levels. Although these observations are based on older data with incomplete coverage, a similar correlation to elevation has been established in one local area studied in detail with newer higher-resolution data. Further mapping with the latest data sets should more clearly elucidate the relationship(s) of the polygons and mounds to elevation over the entire Chryse-Acidalia region and thereby provide more insight into this hypothesis.     

On the existence and stability of liquid water on the surface of mars today

The recent discovery of high concentrations of hydrogen just below the surface of Mars' polar regions by Mars Odyssey has enlivened the debate about past or present life on Mars. The prevailing assumption prior to the discovery was that the liquid water essential for its existence is absent. That assumption was based largely on the calculation of heat and mass transfer coefficients or theoretical climate models. This research uses an experimental approach to determine the feasibility of liquid water under martian conditions, setting the stage for a more empirical approach to the question of life on Mars. Experiments were conducted in three parts: Liquid water's existence was confirmed by droplets observed under martian conditions in part 1; the evolution of frost melting on the surface of various rocks under martian conditions was observed in part 2; and the evaporation rate of water in Petri dishes under Mars-like conditions was determined and compared with the theoretical predictions of various investigators in part 3. The results led to the conclusion that liquid water can be stable for extended periods of time on the martian surface under present-day conditions.     

Martian polar expeditions: problems and solutions.

The Martian polar ice caps are regions of substantial scientific interest, being the most dynamic regions of Mars. They are volatile sinks and thus closely linked to Martian climatic conditions. Because of their scale and the precedent set by the past history of polar exploration on Earth, it is likely that an age of polar exploration will emerge on the surface of Mars after the establishment of a capable support structure at lower latitudes. Expeditions might be launched either from a lower latitude base camp or from a human-tended polar base. Based on previously presented expeditionary routes to the Martian poles, in this paper a "spiral in-spiral out" unsupported transpolar assault on the Martian north geographical pole is used as a Reference expedition to propose new types of equipment for the human polar exploration of Mars. Martian polar "ball" tents and "hover" modifications to the Nansen sledge for sledging on CO2-containing water ice substrates under low atmospheric pressures are suggested as elements for the success of these endeavours.Other challenges faced by these expeditions are quantitatively and qualitatively addressed.     

火星进入气体辐射加热研究进展

针对飞行器进入火星大气时气体辐射加热对防热设计带来不确定性，在简述火星探测和气体辐射研究的发展历程的基础上，对火星进入气体辐射加热研究的进展进行综述。首先，针对火星大气环境描述了气体辐射加热的概念和问题由来。其次，重点综述了近年来火星进入气体辐射加热基础模型的数值和试验研究进展，其中包括：热化学非平衡气体动力学、气体辐射特性和辐射传输的计算模型与方法等数值研究；地面测试设备、试验技术和模拟火星大气环境的气体辐射测量与验证等试验研究。再次，综述了流动辐射耦合和后体气体辐射加热等火星进入器设计方面开展的研究。最后，对未来火星进入气体辐射加热研究进行了展望，提出了研究建议。     

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.     

Adsorption water-related potential chemical and biological processes in the upper martian surface

Mars Odyssey has given strong evidence for the existence of water in the upper martian surface at equatorial latitudes. The water content, which corresponds to the hydrogen in the soil, can regionally reach values up to about 15%. This water is mainly in the form of structurally and partially irreversibly bound "crystal" water, and of reversibly bound and partially unfrozen adsorption water. This adsorption water, which has "liquid-like" properties as a two dimensional fluid or film, can trigger-in the presence of ultraviolet light and in concentrations similar to what has been measured on Mars-photocatalytic processes that are important for martian surface chemistry. The consequences of the diurnally variable presence of adsorption water on the chemistry and hypothetical biological processes at and in the upper martian surface at equatorial and mid-latitudes are discussed in terms of water-related environmental aspects for chemical and hypothetical life processes on Mars.     

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.     

V型皱褶芯材夹层板对流换热性能评价及优化

为考察主动冷却式一体化热防护结构用V型皱褶芯材夹层结构的性能,文章采用Fluent软件模拟受恒定热流载荷皱褶芯材夹层板在强制对流条件下的传热过程,分析其换热特性和流道内流体流动规律;并在分析皱褶芯材夹层板中正三角和倒三角2种流道换热性能差异的基础上,提出相邻流道流向相反的改进方案。该方案可提高冷却剂的利用率,使结构温度分布更加均匀。相比于具有相同几何参数的波纹芯材夹层板,皱褶芯材夹层板具有更好的换热性能,但同时以更大的当量密度和进出口压降损失为代价。比较几种常用的热效率指标,并定义了一种同时考虑换热性能、泵功率和结构质量的热效率指标,再分别以不同的热效率指标为目标函数,对皱褶芯材的几何参数L、W和S进行初步优化设计。