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.     

Experimental hypervelocity impacts: Implication for the analysis of material retrieved after exposure to space environment: Part I. Impacts on aluminium targets

During the last three decades a wide variety of surfaces have been brought back to Earth after being exposed to space environment. The impact features found on these surfaces are used to evaluate the damages caused to spacecraft and can give clues to the characteristics of the orbital debris and meteoroids that created them. In order to derive more precisely the particle parameters and to improve the analysis of projectile remnants, we have performed an extensive analysis of craters caused by the impact of high velocity particles on thick ductile targets, using a micro-particle accelerator. We show that from the geometry of the craters and from the analysis of the remnants it is possible to derive the main characteristics of the projectiles. In particular, using up-to-date instrumentation, scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) spectrometer, we found that even small residues inside craters can be identified. However, this study shows that a velocity resolution better than 1 km/s would be appropriate to obtain a fair calibration of the impact processes on a ductile target. This would allow to decipher with precision impact features on ductile surfaces exposed to space environment.     

A hydrothermal system associated with the Siljan impact structure, Sweden--implications for the search for fossil life on Mars

The Siljan ring structure (368 +/- 1.1 Ma) is the largest known impact structure in Europe. It isa 65-km-wide, eroded, complex impact structure, displaying several structural units, including a central uplifted region surrounded by a ring-shaped depression. Associated with the impact crater are traces of a post-impact hydrothermal system indicated by precipitated and altered hydrothermal mineral assemblages. Precipitated hydrothermal minerals include quartz veins and breccia fillings associated with granitic rocks at the outer margin of the central uplift, and calcite, fluorite, galena, and sphalerite veins associated with Paleozoic carbonate rocks located outside the central uplift. Two-phase water/gas and oil/gas inclusions in calcite and fluorite display homogenization temperatures between 75 degrees C and 137 degrees C. With an estimated erosional unloading of approximately 1 km, the formation temperatures were probably not more than 10-15 degrees C higher. Fluid inclusion ice-melting temperatures indicate a very low salt content, reducing the probability that the mineralization was precipitated during the Caledonian Orogeny. Our findings suggest that large impacts induce low-temperature hydrothermal systems that may be habitats for thermophilic organisms. Large impact structures on Mars may therefore be suitable targets in the search for fossil thermophilic organisms.     

Petrographic criteria for recognizing certain types of impact spherules in well-preserved precambrian successions

Impact spherule layers in sedimentary successions can open a new window on large impacts to complement the better-known record of terrestrial craters. At least six spherule layers have been found in well-preserved late Archean to Paleoproterozoic strata, and a growing body of geochemical evidence indicates they are impact ejecta. The most distinctive characteristics of these impact spherules are: (1) a predominance of highly spherical grains; (2) the presence of grains with unusual shapes such as teardrops and dumbbells; (3) fibroradial aggregates of K-feldspar crystals nucleated on the edges of spherules; and (4) clear internal spots representing both cement-filled vesicles and replaced glass cores, which, in contrast to the nuclei of ooids and armored lapilli, are not always located in the centers of the spherules. These characteristics permit the reliable differentiation of these impact spherules from spheroidal particles of other origins, such as sedimentary ooids or volcanic accretionary lapilli, often with just a hand lens. However, petrographic identification becomes progressively more difficult as the spherules become smaller or more altered. Moreover, impact spherules in other layers of other ages sometimes have different textures, so the ones described here are not representative of all types of impact spherules. They are provided as a starting point for researchers interested in identifying impact spherule layers. Given the visible record of impacts on the Moon and the much greater mass of the Earth, there should be many more impact spherule layers on Earth than have been discovered to date.     

Results of impact simulation for the GIOTTO mission

The European Space Agency (ESA) has decided to carry out a fly-by mission to the comet Halley. The spacecraft will be launched by an ARIANE II and intercept the retrograde Halley orbit on 13 March, 1986. One group of experiments is designed to obtain data on size, mass and composition of the dust in the cometary tail. Because of the very high relative velocity during fly-by (69 km/s) laboratory experiments are necessary to develop and calibrate the experiments. These experiments are presently under way in the laboratory of the Lehrstuhl für Raumfahrttechnik of the Technische Universität München. First results have been obtained for both the Dust Impact Detection System (DIDSY) and the P?articulate Impact Analyzer (PIA). These results are compared with the theoretical models for hypervelocity impact craters. The agreement is good at impact velocities around 15 km/s.     

On biogenicity criteria for endolithic microborings on early Earth and beyond

Micron-sized cavities created by the actions of rock-etching microorganisms known as euendoliths are explored as a biosignature for life on early Earth and perhaps Mars. Rock-dwelling organisms can tolerate extreme environmental stresses and are excellent candidates for the colonization of early Earth and planetary surfaces. Here, we give a brief overview of the fossil record of euendoliths in both sedimentary and volcanic rocks. We then review the current understanding of the controls upon the distribution of euendolithic microborings and use these to propose three lines of approach for testing their biogenicity: first, a geological setting that demonstrates a syngenetic origin for the euendolithic microborings; second, microboring morphologies and distributions that are suggestive of biogenic behavior and distinct from ambient inclusion trails; and third, elemental and isotopic evidence suggestive of biological processing. We use these criteria and the fossil record of terrestrial euendoliths to outline potential environments and techniques to search for endolithic microborings on Mars.     

月表地形环境对着陆器热控系统的影响分析

月球着陆器着陆月表之后的外热流环境与地球轨道卫星外热流环境的最大区别在于月表红外热流的影响.分析月表地形特征是确定月表红外热流影响范围的基础.文章根据调研分析选择了月海地区可能存在的平坦月表、斜坡、石块和撞击坑4种典型地形特征以及月表的热物性参数,并通过计算分析得出了月表地形对着陆器热控系统的一些影响规律--其中平坦月表和斜坡的影响最大,石块和小型撞击坑的影响可以忽略,大型撞击坑可以等效为斜坡的影响.     

Inflatable composite habitat structures for lunar and mars exploration

Recent advances in materials technology have improved the performance capabilities of inflatable, flexible composite structures, which have increased their potential for use in numerous space applications. Space suits, which are comprised of flexible composite components, are a good example of the successful use of inflatable composite structures in space. Space suits employ inflatables technology to provide a stand alone spacecraft for astronauts during extra-vehicular activity. A natural extension of this application of inflatables technology is in orbital or planetary habitat structures. NASA Johnson Space Center (JSC) is currently investigating flexible composite structures deployed via inflation for use as habitats, transfer vehicles and depots for continued exploration of the Moon and Mars.

Inflatable composite structures are being investigated because they offer significant benefits over conventional structures for aerospace applications. Inflatable structures are flexible and can be packaged in smaller and more complex shaped volumes, which result in the selection of smaller launch vehicles which dramatically reduce launch costs. Inflatable composite structures are typically manufactured from materials that have higher strength to weight ratios than conventional systems and are therefore lower in mass. Mass reductions are further realized because of the tailorability of inflatable composite structures, which allow the strength of the system to be concentrated where needed. Flexible composite structures also tend to be more damage tolerant due to their “forgiveness” as compared to rigid mechanical systems. In addition, inflatables have consistently proven to be lower in both development and manufacturing costs.

Several inflatable habitat development programs are discussed with their increasing maturation toward use on a flight mission. Selected development programs being discussed include several NASA Langley Research Center habitat programs that were conducted in the 1960s, the Lawrence Livermore National Laboratory inflatable space station study, the NASA JSC deployable inflatable Lunar habitat study, and the inflatable Mars TransHab study and test program currently ongoing at NASA JSC. Relevant technology developments made by ILC Dover are also presented.     

Endolithic cyanobacteria in halite rocks from the hyperarid core of the Atacama Desert

In the driest parts of the Atacama Desert there are no visible life forms on soil or rock surfaces. The soil in this region contains only minute traces of bacteria distributed in patches, and conditions are too dry for cyanobacteria that live under translucent stones. Here we show that halite evaporite rocks from the driest part of the Atacama Desert are colonized by cyanobacteria. This colonization takes place just a few millimeters beneath the rock surface, occupying spaces among salt crystals. Our work reveals that these communities are composed of extremely resistant Chroococcidiopsis morphospecies of cyanobacteria and associated heterotrophic bacteria. This newly discovered endolithic environment is an extremely dry and, at the same time, saline microbial habitat. Photosynthetic microorganisms within dry evaporite rocks could be an important and previously unrecognized target for the search for life within our Solar System.     

用于航天器贮箱的复合材料层合板低速冲击损伤及其渗漏规律研究

得益于优异的力学性能和减质优势,贮箱复合材料化已成为新一代航天器的重要特征之一,而复合材料贮箱的冲击后渗漏问题须要重点关注。针对一种用于航天器贮箱的含表层机织布复合材料层合板,通过依次开展低速冲击试验、C扫描损伤检测和氦质谱渗漏检测,获取不同能量冲击后层合板的内部分层损伤和渗漏率,并对比分析了机织布分别置于冲击侧和背侧时层合板的渗漏规律。结果表明,将机织布层置于冲击背侧时,层合板的冲击渗漏门槛值显著提高,且发生渗漏时出现目视可见损伤。     

不同密度弹丸对水冰的超高速撞击成坑实验

为了研究冰冻天体表面撞击坑的形成与演化,开展了水冰的超高速撞击成坑实验。使用二级轻气炮发射1.0 mm直径的球形弹丸,以3 km/s、5 km/s和7 km/s速度对圆柱状冰块进行撞击。弹丸材料包括聚碳酸酯和不锈钢两种,冰块温度为253 K。实验观察到了不同弹丸和不同速度条件下,冰块中撞击坑的形貌特征。对撞击坑直径、深度和剖面形状进行了测量,并与文献中铝弹丸对水冰的撞击坑进行了比较分析。获得了水冰撞击坑特征随撞击参数的变化规律,结果表明：撞击坑直径和深度的主导机制不同,坑深主要由弹丸侵彻作用形成,而坑径主要由冰块的剥落所致;坑深比坑径具有更强的对于弹丸密度的依赖性,高密度弹丸撞击坑直径具有比低密度弹丸更强的对于撞击速度的依赖性;撞击坑体积与撞击能量成正比,高密度弹丸形成的撞击坑直径表现出“能量缩比”行为,而低密度弹丸形成的撞击坑直径表现出“动量缩比”行为。     

Diurnal change of MW and IR thermal emissions from lunar craters with relevance to rock abundance

Abnormal “hot spots” during a total eclipse on the lunar surface were revealed by using a ground based infrared (IR) scanner and visible telescope in the early 1960s, which turned out to be “cold spots” on the microwave (MW) brightness temperature distribution at night according to the Chang'E (CE)-1 radiometer's observations. In this paper, a theoretical analysis of radiative transfer is presented to explain this abnormal phenomenon of diurnal changes. Two typical craters, representing the abnormal fresh craters rich in rock abundance and an old one almost free of rocks located at similar latitudes are chosen for comparison of the diurnal temperature change. Using the measurements of CE-1 multi-channel microwave radiometer, brightness temperatures from these two craters are presented and applied to inversions of the physical temperatures of lunar regolith media, based on a three-layer radiative transfer model. The correlation between the diurnal MW and IR thermal changes of the lunar surface and the rock abundance is discussed.     

Impact disruption and recovery of the deep subsurface biosphere

Although a large fraction of the world's biomass resides in the subsurface, there has been no study of the effects of catastrophic disturbance on the deep biosphere and the rate of its subsequent recovery. We carried out an investigation of the microbiology of a 1.76 km drill core obtained from the ～35 million-year-old Chesapeake Bay impact structure, USA, with robust contamination control. Microbial enumerations displayed a logarithmic downward decline, but the different gradient, when compared to previously studied sites, and the scatter of the data are consistent with a microbiota influenced by the geological disturbances caused by the impact. Microbial abundance is low in buried crater-fill, ocean-resurge, and avalanche deposits despite the presence of redox couples for growth. Coupled with the low hydraulic conductivity, the data suggest the microbial community has not yet recovered from the impact ～35 million years ago. Microbial enumerations, molecular analysis of microbial enrichment cultures, and geochemical analysis showed recolonization of a deep region of impact-fractured rock that was heated to above the upper temperature limit for life at the time of impact. These results show how, by fracturing subsurface rocks, impacts can extend the depth of the biosphere. This phenomenon would have provided deep refugia for life on the more heavily bombarded early Earth, and it shows that the deeply fractured regions of impact craters are promising targets to study the past and present habitability of Mars.     

基于小波包变换及相关系数法的复合材料层合板冲击位置识别研究

复合材料较为广泛应用于航空、航天等工程领域,但对冲击载荷十分敏感。因此,对复合材料结构承受的冲击载荷进行在线监测以及冲击位置的实时识别具有重要意义。文章以复合材料层合板为研究对象,基于两个冲击位置的距离越靠近则接收到信号幅频特性相似度越高的特点,采用FBG光纤光栅传感器,通过小波包变换的方法来提取能量特征向量,同时结合相关系数法来实现复合材料层合板的冲击位置识别。在480 mm×480 mm的复合材料层合板上开展冲击实验,8次实验皆完成了冲击位置识别,其中7个点距离误差为0 mm,实现精准识别,另一个点误差在6%以内。     

Microcolonial fungi: survival potential of terrestrial vegetative structures

So far mainly spores or other "differentiated-for-survival" structures were considered to be resistant against extreme environmental constraints (including extraterrestrial challenges). Microcolonial fungi (MCF) are unique growth structures formed by eukaryotic microorganisms inhabiting rock varnish surfaces in terrestrial deserts. They are here proposed as a new object for exobiological study. Sun-exposed desert rocks provide surface habitats with intense solar radiation, a scarce water supply, drastic changes in temperature, and episodic to sporadic availability of nutrients. These challenging conditions reduce the diversity of life to MCF, whose resistance to desiccation and tolerance for ultraviolet (UV) radiation make them survival specialists. Based upon our studies of MCF, we propose that the following mechanisms are universally employed for survival on rock surfaces: (1) compact tissue-like colony organization formed by thermodynamically optimal round cells embedded in extracellular polymeric substances, (2) the presence of several types of UV-absorbing compounds (melanins and mycosporines) and antioxidants (carotenoids, melanins, and mycosporines) that convey multiple stress resistance to desiccation, temperature, and irradiation changes, and (3) intracellular developmental mechanisms typical for these structures.     

Initial design of laboratories for sustainable habitation

An effective and self-sustainable artificial habitat design is essential for human spaceflight and expansion of mankind into orbit or towards other celestial bodies. There are two approaches that need to be implemented in future sustainable habitats: the use of re-cycling technologies in order to gain experience in closed-loop processes and the primary production of resource materials using In Situ Resource Utilisation (ISRU) principles. Various products will be provided and, where applicable, recycled in such a system taking into account basic human factors requirements such as crew work load capacity, safety and well-being, namely:     

Structural health management technologies for inflatable/deployable structures: Integrating sensing and self-healing

Inflatable/deployable structures are under consideration as habitats for future Lunar surface science operations. The use of non-traditional structural materials combined with the need to maintain a safe working environment for extended periods in a harsh environment has led to the consideration of an integrated structural health management system for future habitats, to ensure their integrity. This article describes recent efforts to develop prototype sensing technologies and new self-healing materials that address the unique requirements of habitats comprised mainly of soft goods. A new approach to detecting impact damage is discussed, using addressable flexible capacitive sensing elements and thin film electronics in a matrixed array. Also, the use of passive wireless sensor tags for distributed sensing is discussed, wherein the need for on-board power through batteries or hardwired interconnects is eliminated. Finally, the development of a novel, microencapuslated self-healing elastomer with applications for inflatable/deployable habitats is reviewed.     

一种基于图像的星体表面撞击坑自动提取方法

以星体表面的图像数据为基础,根据撞击坑的向阳面呈亮色调而背阳面呈暗色调的原理,提出了一种基于图像的星体表面撞击坑自动提取方法。该方法先用自适应双阈值分割法对星体表面的光学图像进行分割处理,获取图像中明暗区域的形状和位置信息;再用统计学原理分析明暗区域组成结构、像平面上光照方向,结合相关的约束条件来匹配同一撞击坑的明暗区域,同时拟合出撞击坑的外边缘并确定其半径、位置等信息。实验结果表明,该方法能够从常见的星体表面光学图像中快速、可靠地提取出撞击坑的中心位置和半径大小,具有较宽的普适应性和一定的应用价值。     

Impact craters as biospheric microenvironments, Lawn Hill Structure, Northern Australia

Impact craters on Mars act as traps for eolian sediment and in the past may have provided suitable microenvironments that could have supported and preserved a stressed biosphere. If this is so, terrestrial impact structures such as the 18-km-diameter Lawn Hill Structure, in northern Australia, may prove useful as martian analogs. We sampled outcrop and drill core from the carbonate fill of the Lawn Hill Structure and recorded its gamma-log signature. Facies data along with whole rock geochemistry and stable isotope signatures show that the crater fill is an outlier of the Georgina Basin and was formed by impact at, or shortly before, approximately 509-506 million years ago. Subsequently, it was rapidly engulfed by the Middle Cambrian marine transgression, which filled it with shallow marine carbonates and evaporites. The crater formed a protected but restricted microenvironment in which sediments four times the thickness of the nearby basinal succession accumulated. Similar structures, common on the martian surface, may well have acted as biospheric refuges as the planet's water resources declined. Low-pH aqueous environments on Earth similar to those on Mars, while extreme, support diverse ecologies. The architecture of the eolian crater fill would have been defined by long-term ground water cycles resulting from intermittent precipitation in an extremely arid climate. Nutrient recycling, critical to a closed lacustrine sub-ice biosphere, could be provided by eolian transport onto the frozen water surface.