Long-term preservation of microbial ecosystems in permafrost.

It has been established that significant numbers (up to 10 million cells per gram of sample) of living microorganisms of various ecological and morphological groups have been preserved under permafrost conditions, at temperatures ranging from -9 to -13 degrees C and depths of up to 100 m, for thousands and sometimes millions of years. Preserved since the formation of permafrost in sand-clay sediments of the Pliocene-Quaternary period and in paleosols and peats buried among them, these cells art the only living organisms that have survived for a geologically significant period of time. The complexity of the microbial community preserved varies with the age of the permafrost. Eukaryotes are found only in Holocene sediments; while prokaryotes are found to greater ages, i.e., Pliocene and Pleistocene. The diversity of microorganisms decreases with increasing age of sediments, and as a result cocci and corynebacteria are predominant. Enzyme activity (catalase and hydrolytic enzymes) and photosynthetic pigments (chlorophyll and pheophytin have also been detected in permafrost sediments. These results permit us to outline some approaches to the search for traces of life in the permafrost of Martian sediments by borehole core sampling. It is in the deep horizons (and not on the planet surface), isolated by permafrost from the external conditions, that results similar to those obtained on Earth can be expected.     

A physical and chemical characterization of Martian permafrost as a possible habitat for viable microorganisms.

Data from experiments with model samples show that ion transfer coefficients in the water-rich permafrost on Mars must be three orders of magnitude less than those of terrestrial permafrost. The effects of low temperatures and of carbon dioxide have been accounted for. Exchange between cells and the environment is impeded in Martian permafrost. The microscopic distributional heterogeneity of concentration, pH, Eh, and other physicochemical parameters may be more pronounced in the permafrost of Mars. We present a classification of unfrozen water types in the permafrost that is based on the structures of unfrozen water films and on their functions with respect to cells. Any viable microorganisms on Mars probably exist with minimum metabolism in compact zones with energy carriers and high transfer coefficients. These zones may be microvolumes of unfrozen water in which cells accumulate.     

Role of cell differentiation in high tolerance by prokaryotes of long-term preservation in permafrost

The effect of low temperature on the cell structure of bacteria isolated from permafrost results in structural changes leading to cell differentiation into types of resting cells rangign from spores showing a high endogenous dormancy to typical “dormant” cells of non-spore-forming bacteria showing exogenous dormancy, which is considered to be less highly resistant to extreme conditions in laboratory experiments. In permafrost, dormant cells of non-spore-forming bacteria may demonstrate considerable resistance to long-term freezing and as a result a higher survival level than spore-forming bacteria.     

Martian Buildings: Design loading

Multiplanetary life has been studied by scientists as a way to supply energy or sustain human life in the future. Mars is likely to be man’s first destination, colonization using onsite structural construction would be one of the main options. The first step to designing a reliable building is to know the applied structural loads and to have an accurate design load combination. Due to lack of complete knowledge, short span of recorded data, Martian environment, and hazardous environment that Martian structures face, constructed Martian structures should behave appropriately under the highest likely live, dead and environmental loads either simultaneously or as a worst-case scenario. The present study evaluated and calculated probable Martian structural loads, including live, internal pressure, snow, gravity (dead), dust accumulation, thermal stress, wind, marsquake, asteroid, and meteoroid impact loads and their effects. Information was gathered from previous studies and valid data from Martian landers, rovers and orbiters. Wind loads were calculated based on the over 6.5 years of data recorded by Vikings 1 and 2, temperature and winds for InSight (TWINS) sensor. A wind shear exponent and wind profile have been proposed for a Martian flat terrain construction site. Marsquake lateral loads, frequency content and seismicity were assessed using data from the seismic experiment for interior structure (SEIS) and the Viking 2 seismometer. Considering the high influx of micrometeoroids, their penetration distance, impact loads and their effects on structures were calculated. The annual probability of an asteroid impact on a settlement was assessed for a 30-year mission. A load map for Martian residential buildings that considers the worst-case scenario in which a Martian structure should be designed based on them has been proposed.     

Scientific Objectives and Payloads of Chinese First Mars Exploration

China plans to implement the first Mars exploration mission in 2020. It will conduct global and comprehensive exploration of Mars and high precision and fine resolution detection of key areas on Mars through orbiting, landing and roving. The scientific objectives include studying the Martian morphology and geological structure characteristics, studying the soil characteristics and the water-ice distribution on the Martian surface, studying the material composition on the Martian surface, studying the atmosphere ionosphere and surface climate and environmental characteristics of Mars, studying the physical field and internal structure of Mars and the Martian magnetic field characteristics. The mission equips 12 scientific payloads to achieve these scientific objectives. This paper mainly introduces the scientific objectives, exploration task, and scientific payloads.      

Multifunctional Martian habitat composite material synthesized from in situ resources

The two primary requirements for a Martian habitat structure include effective radiation shielding against the Galactic Cosmic Ray (GCR) environment and sufficient structural and thermal integrity. To significantly reduce the cost associated with transportation of such materials and structures from earth, it is imperative that such building materials should be synthesized primarily from Martian in situ resources. This paper illustrates the feasibility of such an approach. Experimental results are discussed to demonstrate the synthesis of polyethylene (PE) from a simulated Martian atmosphere and the fabrication of a composite material using simulated Martian regolith with PE as the binding material. The radiation shielding effectiveness of the proposed composites is analyzed using results from radiation transport codes and exposure of the samples to high-energy beams that serve as a terrestrial proxy for the GCR environment. Mechanical and ballistic impact resistance properties of the proposed composite as a function of composition, processing parameters, and thermal variations are also discussed to evaluate the multifunctionality of such in situ synthesized composite materials.     

火星空间环境磁场探测研究——高精度磁强计

萤火一号卫星将对火星空间环境磁场实施探测。火星磁场对火星弓激波、磁鞘、电离层、大气等绝大多数空间环境效应都具有重要影响,萤火一号对火星磁场的探测是通过搭载于其上的科学载荷磁强计来实现的。此磁强计在工作原理及具体设计上,考虑了火星轨道严酷的工作环境和科学目标所需的测量要求。通过装星前的地面标定测试,验证了萤火一号磁强计可以在-130～75℃温度范围内测量±256nT以内的磁场,分辨率可达到0.01 nT,带宽内总噪声小于0.03 nT,能够满足萤火一号对火星空间环境探测的需求。     

Evolution of the Martian water cycle.

The current Martian water cycle is extremely asymmetric, with large amounts of vapor subliming off a permanent north polar water ice cap in northern summer, but with no apparent major source of water vapor in the southern hemisphere. Detailed simulations of this process with a three-dimensional circulation model indicate that the summertime interhemispheric exchange (Hadley cell) is very much stronger than transport by eddies in other seasons. As a result, water ice would be distributed globally were it not for the buffering action of regolith soil adsorption which limits the net flux of water vapor off the north polar cap to amounts that are insignificant even on the scale of thousands of years. It has been suggested that the polar layered deposits are the result of exchange on these long time scales, driven by changes in Martian orbital parameters. We therefore are conducting simulations to test the effect of varied orbital parameters on the Martian water cycle. We find that when the perihelion summer pole is charged with a polar water ice cap, large quantities of water are quickly transfered to the aphelion summer pole, setting up an annual cycle that resembles the present one. Thus, the adsorptivity of the Martian regolith may be in the narrow range where it can limit net transport from the aphelion but not the perihelion pole.     

火星磁场产生的原因及其分布

构建了一个可以得到火星赤道面上磁场分布的模型. 模型根据卫星观测数据, 提出了火星电离层、磁层顶和磁尾电流片上都各自通有电流的假设. 由电流的连续性条件可知, 这三种背景条件下的电流之间满足一定关系, 即火星磁层顶上的总电流是电离层上的总电流与磁尾电流片上的总电流之和. 这些电流产生的磁场与太阳风磁场共同构成了火星赤道面上磁场分布. 通过计算发现, 采用这种磁场模型得到的结果与目前卫星所观测的结果以及与采用其他方法得到的结果符合得较好.      

火星探测的微波遥感技术

从微波遥感的角度出发,综述目前国际上对火星的探测现状,列出对微波遥感探测有影响的火星表层土壤、岩层的结构、分布及其介电特性等参数的已有研究结果,分析对火星地壳表层水(或冰)存在可能性及其分布状态的研究动向.结合地球表面微波遥感技术的最新进展,提出用主动与被动微波遥感探测火星表面浅层土壤物质状态和分层结构的可行性分析,初步研讨了火星表层是否有水(或冰)存在的探测方案.      

Martian obstacle and bow shock: origins of boundaries anisotropy

The origin of the anisotropy in the shape of the Martian obstacle and bow shock is analyzed using Mars Global Surveyor observations. The influence of MHD or ion pick-up effects on Martian obstacle position was to be small found, however, localized Martian crustal magnetization increases the thickness of the downstream planetary magnetotail by 500–1000 km in agreement with earlier Phobos 2 observations. A new analytical model is presented for Martian obstacle shape variation for different solar wind ram pressure. Elongation of the Martian BS cross-section in the direction perpendicular to IMF was confirmed while the shift of this cross section in the +Y direction of Martian interplanetary medium reference frame was discovered. The shift of BS cross section in the direction of interplanetary electric field was not revealed thus not conforming the idea that mass-loading play some role in BS control.     

火星土壤物理力学特性分析

火星土壤既是火星表面探测活动的主要探测对象,也是表面探测器设计中需考虑的重要因素之一。火壤的物理力学特性将直接影响着陆器着陆缓冲系统、火星车移动系统等的设计。此外,在着陆器和火星车等表面探测器的地面研制过程中,需要研制模拟火壤,形成模拟的火星表面环境,开展相关的着陆器着陆缓冲性能、火星车移动性能等验证试验。迄今为止,人类已经有多个探测器登陆火星,获取了大量的有关火壤的信息,也研制了多种模拟火壤。通过对已有火壤和模拟火壤的物理力学特性分析,梳理出火壤物理力学特性的参数范围,可为我国火星探测器的研制提供参考。     

Network science landers for Mars

The NetLander Mission will deploy four landers to the Martian surface. Each lander includes a network science payload with instrumentation for studying the interior of Mars, the atmosphere and the subsurface, as well as the ionospheric structure and geodesy. The NetLander Mission is the first planetary mission focusing on investigations of the interior of the planet and the large-scale circulation of the atmosphere. A broad consortium of national space agencies and research laboratories will implement the mission. It is managed by CNES (the French Space Agency), with other major players being FMI (the Finnish Meteorological Institute), DLR (the German Space Agency), and other research institutes. According to current plans, the NetLander Mission will be launched in 2005 by means of an Ariane V launch, together with the Mars Sample Return mission. The landers will be separated from the spacecraft and targeted to their locations on the Martian surface several days prior to the spacecraft's arrival at Mars. The landing system employs parachutes and airbags. During the baseline mission of one Martian year, the network payloads will conduct simultaneous seismological, atmospheric, magnetic, ionospheric, geodetic measurements and ground penetrating radar mapping supported by panoramic images. The payloads also include entry phase measurements of the atmospheric vertical structure. The scientific data could be combined with simultaneous observations of the atmosphere and surface of Mars by the Mars Express Orbiter that is expected to be functional during the NetLander Mission's operational phase. Communication between the landers and the Earth would take place via a data relay onboard the Mars Express Orbiter.     

Annual solar UV exposure and biological effective dose rates on the Martian surface.

The ultraviolet (UV) environment of Mars has been investigated to gain an understanding of the variation of exposure throughout a Martian year, and link this flux to biological effects and possible survival of organisms at the Martian surface. To gain an idea of how the solar UV radiation varies between different regions, including planned landing sites of two future Mars surface missions, we modelled the total solar UV surface flux throughout one Martian year for two different dust scenarios. To understand the degree of solar UV stress on micro-organisms and/or molecules essential for life on the surface of Mars, we also calculated the biologically effective dose (BED) for T7 and Uracil in relevant wavelength regions at the Martian surface as a function of season and latitude, and discuss the biological survival rates in the presence of Martian solar UV radiation. High T7/Uracil BED ratios indicate that even at high latitudes where the UV flux is significantly reduced, the radiation environment is still hostile for life due to the persisting UV-C component of the flux.     

Magnetic levitation-based Martian and Lunar gravity simulator.

Missions to Mars will subject living specimens to a range of low gravity environments. Deleterious biological effects of prolonged exposure to Martian gravity (0.38 g), Lunar gravity (0.17 g), and microgravity are expected, but the mechanisms involved and potential for remedies are unknown. We are proposing the development of a facility that provides a simulated Martian and Lunar gravity environment for experiments on biological systems in a well controlled laboratory setting. The magnetic adjustable gravity simulator will employ intense, inhomogeneous magnetic fields to exert magnetic body forces on a specimen that oppose the body force of gravity. By adjusting the magnetic field, it is possible to continuously adjust the total body force acting on a specimen. The simulator system considered consists of a superconducting solenoid with a room temperature bore sufficiently large to accommodate small whole organisms, cell cultures, and gravity sensitive bio-molecular solutions. It will have good optical access so that the organisms can be viewed in situ. This facility will be valuable for experimental observations and public demonstrations of systems in simulated reduced gravity.     

基于MARSIS的火星低纬度电离层统计特性研究

在对欧空局火星快车探测器搭载的MARSIS雷达的浅表层探测数据进行校准过程中,获得了火星电离层的总电子含量(total electron content,TEC)观测数据。利用该数据,计算火星低纬度地区电离层的峰值电子密度和标高;并对其进行统计分析发现,在低纬度地区,火星冬季电离层的标高和峰值电子密度均较夏季高,即冬季电离层较夏季更显著,且春季电离层的电子密度梯度最大。     

Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen.

Early Earth and early Mars were similar enough such that past geochemical and climatic conditions on Mars may have also been favorable for the origin of life. However, one of the most striking differences between the two planets was the low partial pressure of dinitrogen (pN2) on early Mars (18 mb). On Earth, nitrogen is a key biological element and in many ecosystems the low availability of fixed nitrogen compounds is the main factor limiting growth. Biological fixation of dinitrogen on Earth is a crucial source of fixed nitrogen. Could the low availability of dinitrogen in the primordial Martian atmosphere have prevented the existence, or evolution of Martian microbiota? Azotobacter vinelandii and Azomonas agilis were grown in nitrogen free synthetic medium under various partial pressures of dinitrogen ranging from 780-0 mb (total atmosphere=1 bar). Below 400 mb the biomass, cell number, and growth rate decreased with decreasing pN2. Both microorganisms were capable of growth at a pN2 as low as 5 mb, but no growth was observed at a pN2 < or = 1 mb. The data appear to indicate that biological nitrogen fixation could have occurred on primordial Mars (pN2=18 mb) making it possible for a biotic system to have played a role in the Martian nitrogen cycle. It is possible that nitrogen may have played a key role in the early evolution of life on Mars, and that later a lack of available nitrogen on that planet (currently, pN2=0.2 mb) may have been involved in its subsequent extinction.     

火星大气模型参数对MSL气动特性的影响

火星大气与地球大气截然不同,飞行器在进入火星时气动特性不同于地球再入. 大气模型的差异主要表现为气体组份、密度和温度等物理参数. 针对火星进入器MSL在进入-下降-着陆过程中的高超声速进入段,利用三维并行程序求解耦合真实气体模型的流体动力学Navier-Stokes方程,分析MSL进入火星大气时大气模型参数对进入器气动特性的影响. 结果表明,通过与海盗号飞行数据的对比,验证了所采用的火星气体模型和计算方法,且其与NASA的 LAURA代码气动特性计算结果也较为一致;大气模型气体性质,即CO₂环境对进入器阻力系数和俯仰力矩系数影响较大,利用空气得到的计算和实验数据必须考虑CO₂效应;密度增大促进了化学非平衡效应,但对进入器气动特性基本没有影响;温度升高大大增强了化学非平衡效应,而对进入器气动特性影响较小.      

Stable carbon isotopes: possible clues to early life on Mars.

Organic and inorganic carbon in terrestrial near-surface environments are characterized by a marked difference in their 13C/12C ratios which can be traced back in the Earth's sedimentary record over almost 4 billion years. There is no doubt that the bias in favour of 12C displayed by biogenic matter derives, for the most part, from the isotope-selecting properties of the carbon-fixing enzyme (ribulose-1,5-bisphosphate carboxylase) that is operative in the principal photosynthetic pathway and promotes most of the carbon transfer from the non-living to the living realm. Postulating a universality of biological principles in analogy to the proven universality of the laws of physics and chemistry, we may expect enzymatic reactions in exobiological systems to be beset with B similar kinetic fractionation effects. Hence, the retrieval from the oldest Martian sediments of isotopic fractionations between reduced and oxidized (carbonate) carbon may substantially constrain current conjectures on the possible existence of former life on Mars.     

Atmospheric dynamics on Venus and Mars

New results from Pioneer Orbiter observations indicate a continued vortex organization of the cloud level atmosphere in either hemisphere, centered over respective poles. Significant changes in the magnitude of the cloud level zonal circulation over a period of several years have been detected. A strong signature of the solar tidal circulation has been detected in the atmospheric circulation with the lowest speeds occurring in equatorial latitudes about 20° upstream of the sub-solar point. Finally, a solar-locked persistent spatial structure has been discovered in the variance of the ultraviolet brightness measured from brightness normalized images of Venus. Vega balloons (drifting at about 53 km altitude near 7°N and 7°S latitudes) have also provided some unique observations of atmospheric circulation, significant among them being the strong vertical motions, the zonality of their drift speeds as well as a significant temperature difference between the two balloons. The temperature difference which amounts to 6.5°K on average is currently being interpreted as a temperature variation with longitude or time.

Diagnostic modelling efforts towards simulating the atmospheric circulation on Venus are continuing and have provided some clues about the processes that maintain them but have not yet been successful in explaining the superrotation of the atmosphere.

Knowledge of the Martian atmospheric dynamics on the other hand is still limited by lack of adequate observations. Numerical modelling of the Martian atmosphere continues to provide most of the information about the atmospheric circulation. The situation regarding the paucity of observations should improve with the completion of the proposed Mars Observer mission. The low circular polar orbit planned provides an excellent opportunity to study the Martian atmosphere.