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.      

Mercury: can any ice exist at subpolar regions?

The heat transfer in a regolith subsurface layer of thickness 20 m has been theoretically simulated for the areas near Mercury's north pole aiming at the clarification of the possible existence of subsurface ice formations of different form. The paper considers different models of the icy regolith structure and composition: pure uniform amorphous ice; a porous dispersive system with ice-filled pores and voids; permafrost. For comparison the heat transfer in dry iceless regolith has been considered as well. It has been shown that the line of maximum distribution of subsurface icy formations depends on the icy regolith model, but for any one in the “hot” regions it does not go below 70°. For the “cool” regions this line has been shown to go from 5° to 10° southward than that for the “hot” ones. The possible thickness of icy regolith near the pole has been estimated for different models assuming an interior heat flow of 15 mW m⁻². It has been shown that the maximum thickness of this layer takes place at the pole and is equal to 10 km for any model.     

Mechanical behavior of the metal parts welded with extraterrestrial regolith simulant by the solar concentrator in ISRU & ISRF application

The use of in-situ resources plays an important role on future extraterrestrial human activities for the facility repair and habitat construction, especially in sustainable space exploration of Moon and Mars. A method of the metal welded with extraterrestrial regolith simulant using solar processing under ambient conditions is presented. Metal parts are made of Q235B ferroalloy and TA2 titanium alloy into standard tensile members according to the ASTM code. They are disconnected from the middle in advance, and then welded together with lunar and Martian regolith simulant under ambient conditions, respectively. The entire welding process and precautions are detailed. Additionally, the mechanical behavior of weldments is characterized regarding their tensile strength. Furthermore, the fusion zone of weldments is studied by Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) measurements. The results show that it is possible to weld metal parts together with extraterrestrial regolith simulant by the solar concentrator. The average ultimate tensile strength of ferroalloy specimens welded with lunar and Martian regolith simulant is 2.94 MPa and 1.66 MPa; The average ultimate tensile strength of titanium alloy specimens welded with lunar and Martian regolith simulant is 4.95 MPa and 2.59 MPa. Moreover, the failure mode of all weldments was brittle failure. The welding joints strength derives from the phases that the regolith as the solder fusing into ferroalloys in a homogeneous way and titanium alloys in an inhomogeneous way. The presented method may provide a new thought for astronaut assistance associating with repairing and fabricating in subsequent Moon and Mars missions.     

Hydrocode modelling of hypervelocity impacts on ice

Experimental data are now widely available for the size of craters resulting from hypervelocity impacts of millimetre scale projectiles onto water ice targets. At such size scales the bowl shaped crater formed in ductile materials, or in larger scale impacts, is here surrounded by a large spallation zone due to the brittle nature of the ice. Modelling of these impacts therefore has to take account of this spallation. Here we used the iSALE2 hydrocode to simulate such impacts and compared the results to experimental data. We found that it was possible to reproduce the experimental data over a range of speeds (1–7 km s⁻¹) for aluminium and copper projectiles. Initially, to reproduce the large spallation regions around the craters it was assumed that above a certain degree of damage, material was removed by spallation. However this simple one-parameter model failed to model the crater depth adequately. Accordingly, to obtain the best agreement of the simulations with the experimental data, a two-step ice strength was introduced, whereby above a critical amount of damage (0.95), the yield strength reduced from 1 MPa (intact) to 70 kPa (damaged). As a result, experimental data for crater depth and diameter and the results of the simulations agree to within 6% for diameter and 5% for depth over the impact energy range used in the experiments (1–240 J).     

Phobos regolith simulants PGI-1 and PCA-1

The Martian moon Phobos is the target of the upcoming JAXA Martian Moons eXploration (MMX) mission. There are currently no known samples of Phobos, so spacecraft hardware testing and scientific studies require Phobos regolith simulants. Here, we present two new Phobos regolith simulants: Phobos Captured Asteroid-1 (PCA-1) and Phobos Giant Impact (PGI-1). These two simulants reflect the two hypotheses for Phobos’s formation, and thus the two broad possibilities for composition. This work follows previous efforts to document the development of mineralogically accurate simulants, in an effort to overcome past pitfalls with inappropriate uses of simulants. We report physical and geotechnical properties of PCA-1 and PGI-1, including their reflectance spectra, grain size distributions, abrasivity, cohesion, strength, and hardness. Our intent is for PCA-1 and PGI-1 to be open standards for Phobos simulants, and we present the simulant recipes and production methodology for use and modification by the community.     

单层板撞击成坑声发射辨识及参数估计研究

空间碎片撞击航天器的威胁对发展在轨感知系统提出需求,为研制基于声发射技术的感知系统,有必要研究利用声发射波形分析对防护结构进行损伤模式辨识的方法。文章利用超声传感器进行了铝弹丸超高速撞击单层板的声发射信号采集实验及其数值仿真,并对波形在时域和频域内进行分析,结果表明:声发射波形的主波谷值随撞击速度增加而线性增加,直到防护结构被击穿;声发射波形中的高频分量与低频分量幅值之比存在一个区别成坑模式与击穿模式的阈值。基于上述结果提出了一种在撞击弹丸尺寸已知条件下辨识成坑模式并对其撞击速度及其弹坑尺寸进行估计的方案。     

Large-scale impact cratering on the terrestrial planets

Impact cratering as a geologic process on the terrestrial planets is addressed. The crater densities on the Earth and Moon form the basis for a standard flux-time curve, which can be used to date unsampled planetary surfaces and constrain the temporal history of endogenic geologic processes. The attached uncertainties and the shape of the flux curve (a rapid exponential decay for the period 4.6 – 4.0 by, followed by the establishment of a constant fluid by 3.5 – 3.0 by which continues more or less to the present) are such that only very old (3.8 by) and very young ( 1.0 by) surfaces can be dated with some confidence. Dating of intermediate-aged surfaces is more imprecise; a problem which is most significant for the geologic history of Mars.

The cratering mechanics of simple craters are fairly well understood. A transient cavity of roughly parabolic cross-section results from the combined excavation and displacement of the target rocks by the cratering flow-field, which can be approximated by the Z-model derived from shallow-buried explosive events. The walls of the transient crater are unstable and slump inwards, resulting in a final bowl-shaped crater partially filled by breccia. The formation process of larger, shallow complex structures is less well understood. Recent models favor the complete collapse of the initial cavity, with the dynamic uplift of the excavated cavity floor. Regardless of the driving force for uplift, yield strength of the target rocks must be drastically reduced during cavity modification by an, as yet, imprecisely known process.

The formation of large impact basins had a profound effect on planetary evolution. They define the basic tectonic and stratigraphic framework of the Moon and their secondary effects lasted for 10⁸ y. The evidence is less compelling from other planets, but a general feature appears to be the concentration of later endogenic activity in and around basins. On Earth, it is possible that basin-formation contributed to the establishment of the dichotomy between proto-continental and proto-oceanic crusts. The effects of impact continue into recent geologic history and may be linked to major biological changes on Earth, such as at the Cretaceous-Tertiary boundary.     

Gas permeability and flow characterization of simulated lunar regolith

Recent discoveries of water ice trapped within lunar topsoil (regolith) have placed a new emphasis on the recovery and utilization of water for future space exploration. Upon heating the lunar ice to sublimation, the resulting water vapor could theoretically transmit through the lunar regolith, to be captured on the surface. As the permeability of lunar regolith is essential to this process, this paper seeks to experimentally determine the permeability and flow characteristics of various gas species through simulated lunar regolith (SLR). Two different types of SLR were compacted and placed into the permeability setup to measure the flow-rate of transmitted gas through the sample. Darcy’s permeability constant was calculated for each sample and gas combination, and flow characteristics were determined from the results. The results show that Darcy’s permeability constant varies with SLR compaction density, and identified no major difference in permeable flow between the several tested gas species. Between the two tested SLR types, JSC-1A was shown to be more permeable than NU-LHT under similar conditions. In addition, a transition zone was identified in the flow when the gas pressure differential across the sample was less than ∼40 kPa.     

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.     

“嫦娥4号”月球背面着陆区月壳及深部结构特征

深部月壳和月幔物质结构是月球科学探测的关键问题之一。“嫦娥4号”初步将月球背面南极—艾肯（South Pole-Aitken,SPA）盆地内的冯·卡门（Von Kármán）撞击坑作为着陆点,具有重要的科学研究价值。结合月球重力、地形、布格重力、月壳厚度等地球物理数据,综合对冯·卡门撞击坑的月壳及其深部结构特征进行了分析。结果显示：冯·卡门撞击坑重复撞击到南部的冯·卡门M撞击坑上,后者的中央峰具有明显的布格正重力异常和线性的布格重力梯度特征,显示出高密度的幔部物质向上涌起;冯·卡门撞击坑极有可能穿透了该区域的整个月壳,并挖掘出了深部月幔的物质;该区域南部月壳厚度较薄小于5 km,北部平均月壳厚度在15～20 km,月壳平均密度为2 630 kg·m^-3,比背面高地月壳密度高,且平均孔隙度为9%,低于月球的平均孔隙度12%。     

地外天体潜入式探测典型案例分析及展望

针对地外天体星壤剖面的潜入式探测任务,对星球表面热场、星壤剖面原位力学特性等科学目标探测的基本原理、实现方案和典型案例进行了资料调研与分析,并阐明了国际上开展地外天体星壤剖面潜入式探测活动的目的和科学意义。在此基础上,提出了我国月面采样科学目标拓展方案以及我国开展潜入式探测的预先研究规划,对蠕动掘进和冲击贯入式探测方案的基本原理和应用前景进行了分析。     

A drilling tool design and in situ identification of planetary regolith mechanical parameters

The physical and mechanical properties as well as the heat flux of regolith are critical evidence in the study of planetary origin and evolution. Moreover, the mechanical properties of planetary regolith have great value for guiding future human planetary activities. For planetary subsurface exploration, an inchworm boring robot (IBR) has been proposed to penetrate the regolith, and the mechanical properties of the regolith are expected to be simultaneously investigated during the penetration process using the drilling tool on the IBR. This paper provides a preliminary study of an in situ method for measuring planetary regolith mechanical parameters using a drilling tool on a test bed. A conical-screw drilling tool was designed, and its drilling load characteristics were experimentally analyzed. Based on the drilling tool-regolith interaction model, two identification methods for determining the planetary regolith bearing and shearing parameters are proposed. The bearing and shearing parameters of lunar regolith simulant were successfully determined according to the pressure-sinkage tests and shear tests conducted on the test bed. The effects of the operating parameters on the identification results were also analyzed. The results indicate a feasible scheme for future planetary subsurface exploration.     

月球撞击坑辐射纹的形成和消失机制及可能的年代学应用

辐射纹是年轻撞击坑周缘呈辐射状分布的明亮细条纹,是月表最显著的地貌特征之一,也是月球科学领域热点研究之一.根据目前对于月球撞击坑辐射纹的形成和类型的认识,分析辐射纹消失相关的空间风化、撞击导致的物质混合等地质过程;比较不同形成年龄撞击坑辐射纹的光学成熟度(OMAT)剖面,发现溅射物逐渐成熟过程中OMAT剖面的演变过程,...     

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。     

Planetary protection and the search for life beneath the surface of Mars.

The search for traces of extinct and extant life on Mars will be extended to beneath the surface of the planet. Current data from Mars missions suggesting the presence of liquid water early in Mars' history and mathematical modeling of the fate of water on Mars imply that liquid water may exist deep beneath the surface of Mars. This leads to the hypothesis that life may exist deep beneath the Martian surface. One possible scenario to look for life on Mars involves a series of unmanned missions culminating with a manned mission drilling deep into the Martian subsurface (approximately 3Km), collecting samples, and conducting preliminary analyses to select samples for return to earth. This mission must address both forward and back contamination issues, and falls under planetary protection category V. Planetary protection issues to be addressed include provisions stating that the inevitable deposition of earth microbes by humans should be minimized and localized, and that earth microbes and organic material must not contaminate the Martian subsurface. This requires that the drilling equipment be sterilized prior to use. Further, the collection, containment and retrieval of the sample must be conducted such that the crew is protected and that any materials returning to earth are contained (i.e., physically and biologically isolated) and the chain of connection with Mars is broken.     

Decomposition of sodium formate and L- and D-alanine in the Pampas de La Joya soils: Implications as a new geochemical analogue to Martian regolith

The organic compounds on the Martian surface are still undetectable by the previous Viking mission that has been sent to Mars even though they are expected to be there by exogenous and/or endogenous synthesis. The high abiotic reactivity has been the most acceptable explanation for the apparently absence of organic matter in the regolith.     

Martian cloud systems: Current knowledge and future observations

In this paper we summarise the current understanding of Martian condensate and dust clouds. The paper is particularly concerned with the spatial, temporal and seasonal characteristics of the clouds. The condensate clouds are composed of water and ice particles and occasionally CO₂ particles. Dust clouds are composed of material from the surface and redistributed over the planet through the weather systems. The apparent lack of annual reproductivity of these dust storms forms a major unresolved problem. We discuss in this paper the types of observations needed in future space missions, in particular the requirements for the NASA Mars Geochemical Climatology Orbiter Mission planned for the end of this decade.     

Radar detection of subsurface features on Mars

The structure of the pulse radar signal reflected from continuously changing layered Martian crust is investigated theoretically. As a simple model of stratigraphy, we considered one layer with electrodynamics’ parameters increasing or decreasing exponentially upon a depth laying on monolith base and covered by homogeneous layer. This exponential changing of electromagnetic properties of the layer is assumed due to exponential changing of porosity (or saturation) in the bedrocks with pores filled by seawater. The conditions of subsurface features resolution are obtained. It is shown that the sign and value for gradient of the electromagnetic properties change can be resolved from the reflection peaks trend. These results are important for subsurface detection of liquid water on Mars by orbit-based radars.     

A facility for simulating Titan’s environment

As a result of measurements acquired by the Cassini–Huygens mission of Titan’s near surface atmospheric composition and temperature, Titan conditions can now be simulated in the laboratory and samples can subsequently be subjected to those conditions. Titan demonstrates an active hydrological-like cycle with its thick atmosphere, dynamic clouds, polar lakes of methane and ethane, moist regolith, and extensive fluvial erosive features. Unlike Earth, Titan’s hydrological-like cycle likely involves several constituents, primarily methane and ethane. Here the properties of a new Titan simulation facility are presented, including conceptual methodology, design, implementation, and performance results. The chamber maintains Titan’s surface temperature and pressure, and the sample cryogenic liquids undergoing experimentation are condensed within the chamber itself. During the experiments, the evaporation rates of the sample liquids are directly determined by continually measuring mass. Constituents are analyzed utilizing a Fourier Transform Infrared Spectroscopy (FTIR), and vapor concentrations are determined using a gas chromatograph fitted with a Flame Ionization Detector (FID). All pertinent data is logged via computer. Under laboratory conditions, the direct measurements of the evaporation rates of methane, ethane, and mixtures thereof can be achieved. Among the processes to be studied are the effects of regolith on transport from the subsurface to the atmosphere, the freezing point depression effects of dissolved nitrogen, and the solubility of various relevant organic compounds.