Assessment of Mars Exploration Rover landing site predictions

Comprehensive analyses of remote sensing data during the three-year effort to select the Mars Exploration Rover landing sites at Gusev crater and at Meridiani Planum correctly predicted the atmospheric density profile during entry and descent and the safe and trafficable surfaces explored by the two rovers. The Gusev crater site was correctly predicted to be a low-relief surface that was less rocky than the Viking landing sites but comparably dusty. A dark, low-albedo, flat plain composed of basaltic sand and haematite with very few rocks was expected and found at Meridiani Planum. These results argue that future efforts to select safe landing sites based on existing and acquired remote sensing data will be successful. In contrast, geological interpretations of the sites based on remote sensing data were less certain and less successful, which emphasizes the inherent ambiguities in understanding surface geology from remotely sensed data and the uncertainty in predicting exactly what materials will be available for study at a landing site.     

Meridiani Planum and the global hydrology of Mars

The Opportunity Mars Exploration Rover found evidence for groundwater activity in the Meridiani Planum region of Mars in the form of aeolian and fluvial sediments composed of sulphate-rich grains. These sediments appear to have experienced diagenetic modification in the presence of a fluctuating water table. In addition to the extensive secondary aqueous alteration, the primary grains themselves probably derive from earlier playa evaporites. Little is known, however, about the hydrologic processes responsible for this environmental history-particularly how such extensive evaporite deposits formed in the absence of a topographic basin. Here we investigate the origin of these deposits, in the context of the global hydrology of early Mars, using numerical simulations, and demonstrate that Meridiani is one of the few regions of currently exposed ancient crust predicted to have experienced significant groundwater upwelling and evaporation. The global groundwater flow would have been driven primarily by precipitation-induced recharge and evaporative loss, with the formation of the Tharsis volcanic rise possibly playing a role through the burial of aquifers and induced global deformation. These results suggest that the deposits formed as a result of sustained groundwater upwelling and evaporation, rather than ponding within an enclosed basin. The evaporite formation coincided with a transition to more arid conditions that increased the relative impact of a deep-seated, global-scale hydrology on the surface evolution.     

A volcanic environment for bedrock diagenesis at Meridiani Planum on Mars

Exposed bedrocks at Meridiani Planum on Mars display chemical and mineralogical evidence suggesting interaction with liquid water. On the basis of morphological observations as well as high abundances of haematite and sulphate minerals, the rocks have been interpreted as sediments that were deposited in a shallow body of briny water with subsequent evaporation leaving behind the sulphate minerals. The iron-sulphur mineralization at Meridiani has also been inferred to be analogous to that produced during oxidative weathering of metal sulphide minerals, such as occurs at acid mine drainage sites. Neither of these interpretations, however, is consistent with the chemical composition of the rocks. Here we propose an alternative model for diagenesis of Meridiani bedrock that involves deposition of volcanic ash followed by reaction with condensed sulphur dioxide- and water-bearing vapours emitted from fumaroles. This scenario does not require prolonged interaction with a standing body of surface water and may have occurred at high temperatures. Consequently, the model invokes an environment considerably less favourable for biological activity on Mars than previously proposed interpretations.     

Planetary science: bedrock formation at Meridiani Planum

The Mars Exploration Rover Opportunity discovered sulphate-rich sedimentary rocks at Meridiani Planum on Mars, which are interpreted by McCollom and Hynek as altered volcanic rocks. However, their conclusions are derived from an incorrect representation of our depositional model, which is upheld by more recent Rover data. We contend that all the available data still support an aeolian and aqueous sedimentary origin for Meridiani bedrock.     

Impact origin of sediments at the Opportunity landing site on Mars

Mars Exploration Rover Opportunity discovered sediments with layered structures thought to be unique to aqueous deposition and with minerals attributed to evaporation of an acidic salty sea. Remarkable iron-rich spherules were ascribed to later groundwater alteration, and the inferred abundance of water reinforced optimism that Mars was once habitable. The layered structures, however, are not unique to water deposition, and the scenario encounters difficulties in accounting for highly soluble salts admixed with less soluble salts, the lack of clay minerals from acid-rock reactions, high sphericity and near-uniform sizes of the spherules and the absence of a basin boundary. Here we present a simple alternative explanation involving deposition from a ground-hugging turbulent flow of rock fragments, salts, sulphides, brines and ice produced by meteorite impact. Subsequent weathering by intergranular water films can account for all of the features observed without invoking shallow seas, lakes or near-surface aquifers. Layered sequences observed elsewhere on heavily cratered Mars and attributed to wind, water or volcanism may well have formed similarly. If so, the search for past life on Mars should be reassessed accordingly.     

Implications for hydrologic processes on Mars from extensive bedrock outcrops throughout Terra Meridiani

Grey haematite was recently detected in the Terra Meridiani region of Mars by the Thermal Emission Spectrometer onboard the Mars Global Surveyor spacecraft. The formation of haematite on Earth often requires liquid water to be present for long periods of time, making this an important target for deciphering the history of water on Mars. The Mars Exploration Rover Opportunity landed in Meridiani early in 2004 and has since discovered light-toned bedrock outcrops rich in chemical and textural signatures of long-term water interaction locally at the landing site. Here I use remote sensing data to show that the light-toned outcrops at the landing site are not a local phenomenon. Instead, they are observable throughout the haematite-bearing plains in both visible and thermal infrared remote sensing data. Moreover, the light-toned material outcrops around much of the margin and is mappable for hundreds of kilometres to the north, east and west of the plains. I infer that 3 x 10(5) km(2) of this material is exposed over 20 degrees of longitude, indicating the extended presence of surface or near-surface water over a large region of Mars.     

基于视觉的火星探测器着陆运动参数估计

火星探测是我国深空探测的重要目标之一,精确估计火星探测器自主着陆时的运动参数是实现自主着陆的前提.在探测器所携带相机内参数已知的情况下,研究2幅图片中特征点之间的对应关系,得出火星探测器空间三维运动信息,以实现其运动参数估计.首先进行特征点检测,然后进行特征点匹配,根据匹配结果估计出基础矩阵F;然后进行本质矩阵的计算、姿态解算和幅值恢复,对所得运动参数进行非线性优化;最后通过仿真实验验证了上述方法的有效性.     

Water alteration of rocks and soils on Mars at the Spirit rover site in Gusev crater

Gusev crater was selected as the landing site for the Spirit rover because of the possibility that it once held a lake. Thus one of the rover's tasks was to search for evidence of lake sediments. However, the plains at the landing site were found to be covered by a regolith composed of olivine-rich basaltic rock and windblown 'global' dust. The analyses of three rock interiors exposed by the rock abrasion tool showed that they are similar to one another, consistent with having originated from a common lava flow. Here we report the investigation of soils, rock coatings and rock interiors by the Spirit rover from sol (martian day) 1 to sol 156, from its landing site to the base of the Columbia hills. The physical and chemical characteristics of the materials analysed provide evidence for limited but unequivocal interaction between water and the volcanic rocks of the Gusev plains. This evidence includes the softness of rock interiors that contain anomalously high concentrations of sulphur, chlorine and bromine relative to terrestrial basalts and martian meteorites; sulphur, chlorine and ferric iron enrichments in multilayer coatings on the light-toned rock Mazatzal; high bromine concentration in filled vugs and veins within the plains basalts; positive correlations between magnesium, sulphur and other salt components in trench soils; and decoupling of sulphur, chlorine and bromine concentrations in trench soils compared to Gusev surface soils, indicating chemical mobility and separation.     

“荧惑守心”问题之我见

历史上有几次不曾实际发生的"荧惑守心"事件,可能是心宿二的伴星蓝矮星的新星爆发,周期约500多年.甲骨文"新大星并火"可以解释为新大星"合并"入大火星,可能也是心宿二伴星的一次爆发.     

用多轴线投影法测设拱坝的探索

从与各种测设拱坝的方法的比较中，提出用多轴线投影法测设拱坝．它避免了其他测设方法中的困难，加快了测设速度，又容易达到较高的测设精度，是一种简易而又较好的测设方法．     

Research on the relationship between site function and environment at the site of Zhongba,Chongqing City, China

The Zhongba site has been demonstrated to be a location of salt production based on multi-disciplinary research including salt archaeology,environmental archaeology,zooarchaeology,paleobotany,and other natural science examinations.The continuity of salt production from the Han Dynasty to the present day as understood primarily from ancient texts can now be traced back to even earlier times. Based on the characteristics of cultural layer deposits,features,and artifacts,Zhongba can be clearly distinguished from known settlements,and from bronze,iron,pottery and porcelain workshops.According to various natural science examinations,the major impurities in local salt brine are also found in floor features,brine troughs,and rounded bottom pots at the site even though NaCl itself was not preserved.These traces were left over from the salt production process rather than being naturally deposited.Zhongba and its constituent features and artifacts share many common characters with other salt production sites around the world.Consequently,the Zhongba site can be confidently identified as a salt production site where activity continued for several thousand years.The formation of the site cannot be separated from salt production,and it is also highly related to its natural environment.     

放射性废物处置某场址地球化学工程屏障研究

针对某放射性废物处置场址的天然屏障性能差,提出建造折叠式"之"字形地球化学工程屏障,将处置物释放出的核素垂向固定在场址范围内。屏障的机理是,核素铀、锶的迁移形式分别为:UO2(CO3)22-和Sr2+,而性能相反,且处置层为表生强氧化带,降水入渗强烈,不宜建还原性屏障;故对铀和锶依次建造:阴离子吸附屏障和阳离子吸附屏障,形成可连续渗流的双重屏障。屏障的砂土物料取自场址附近,成本极低。经室内模拟实验结果表明,铀和锶等核素通过其屏障时的分配系数值都在103量级。     

县域自然资源可持续利用探讨

探讨了县域资源可持续利用的原则,并以四川省洪雅县为例,在分析其资源环境特征以及自然资源利用现状和存在问题的基础上,提出了该县资源可持续利用的相应对策.     

Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site

Measuring stress changes within seismically active fault zones has been a long-sought goal of seismology. One approach is to exploit the stress dependence of seismic wave velocity, and we have investigated this in an active source cross-well experiment at the San Andreas Fault Observatory at Depth (SAFOD) drill site. Here we show that stress changes are indeed measurable using this technique. Over a two-month period, we observed an excellent anti-correlation between changes in the time required for a shear wave to travel through the rock along a fixed pathway (a few microseconds) and variations in barometric pressure. We also observed two large excursions in the travel-time data that are coincident with two earthquakes that are among those predicted to produce the largest coseismic stress changes at SAFOD. The two excursions started approximately 10 and 2 hours before the events, respectively, suggesting that they may be related to pre-rupture stress induced changes in crack properties, as observed in early laboratory studies.     

地方高等师范院校英语专业人才培养模式探析——以曲靖师范学院为例

培养目标是教育活动的出发点和依据,也是教育活动的归宿。在全球化进程日愈加快的21世纪,地方高等师范院校面临着更多的挑战和生存危机,必须改革旧的人才培养模式。如何确立知识经济时代师范类院校新型英语人才的培养模式对学校的教学工作具有重要的指导意义;探究和论证培养新型师范英语人才的必要性,对构建新型地方高等师范英语人才的培养模式意义重大。     

WTO环境下对建设单位施工现场甲方代表的要求

论述了WTO环境下如何当好建设单位施工现场甲方代表，对甲方代表的素质，在工作中应注意的问题及与各方的关系处理进行了探讨。     

Heat treatment and associated early modern human behaviors in the Late Paleolithic at the Shuidonggou site

Unearthed artifacts and cultural relics from the Shuidonggou site revealed extensive information and insights regarding the activities of early modern humans.A series of experimental research and physical analysis suggest that stone artifacts from Locality 2 and Locality 12 have undergone heat treatment.The utilization ratio and knapping properties of raw materials were consequently enhanced.Heat treatment technology reflects the production capacities and the survival strategies in the Upper Paleolithic period.This discovery indicates the earliest existence of this technology in the East Asia and thus confirms a wider geographic distribution of this technology which provides new perspectives and evidence for understanding the associated early modern human behaviors.