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821.
822.
Sugitani K Lepot K Nagaoka T Mimura K Van Kranendonk M Oehler DZ Walter MR 《Astrobiology》2010,10(9):899-920
Morphologically diverse structures that may constitute organic microfossils are reported from three remote and widely separated localities assigned to the ca. 3400?Ma Strelley Pool Formation in the Pilbara Craton, Western Australia. These localities include the Panorama, Warralong, and Goldsworthy greenstone belts. From the Panorama greenstone belt, large (> 40?μm) lenticular to spindle-like structures, spheroidal structures, and mat-forming thread-like structures are found. Similar assemblages of carbonaceous structures have been identified from the Warralong and Goldsworthy greenstone belts, though these assemblages lack the thread-like structures but contain film-like structures. All structures are syngenetic with their host sedimentary black chert, which is associated with stromatolites and evaporites. The host chert is considered to have been deposited in a shallow water environment. Rigorous assessment of biogenicity (considering composition, size range, abundance, taphonomic features, and spatial distributions) suggests that cluster-forming small (<15 μm) spheroids, lenticular to spindle-like structures, and film-like structures with small spheroids are probable microfossils. Thread-like structures are more likely fossilized fibrils of biofilm, rather than microfossils. The biogenicity of solitary large (>15?μm) spheroids and simple film-like structures is less certain. Although further investigations are required to confirm the biogenicity of carbonaceous structures from the Strelley Pool Formation, this study presents evidence for the existence of morphologically complex and large microfossils at 3400?Ma in the Pilbara Craton, which can be correlated to the contemporaneous, possible microfossils reported from South Africa. Although there is still much to be learned, they should provide us with new insights into the early evolution of life and shallow water ecosystems. 相似文献
823.
Cousins CR Griffiths AD Crawford IA Prosser BJ Storrie-Lombardi MC Davis LE Gunn M Coates AJ Jones AP Ward JM 《Astrobiology》2010,10(9):933-951
The Panoramic Camera (PanCam) instrument will provide visible-near IR multispectral imaging of the ExoMars rover's surroundings to identify regions of interest within the nearby terrain. This multispectral capability is dependant upon the 12 preselected "geological" filters that are integrated into two wide-angle cameras. First devised by the Imager for Mars Pathfinder team to detect iron oxides, this baseline filter set has remained largely unchanged for subsequent missions (Mars Exploration Rovers, Beagle 2, Phoenix) despite the advancing knowledge of the mineralogical diversity on Mars. Therefore, the geological filters for the ExoMars PanCam will be redesigned to accommodate the astrobiology focus of ExoMars, where hydrated mineral terrains (evidence of past liquid water) will be priority targets. Here, we conduct an initial investigation into new filter wavelengths for the ExoMars PanCam and present results from tests performed on Mars analog rocks. Two new filter sets were devised: one with filters spaced every 50?nm ("F1-12") and another that utilizes a novel filter selection method based upon hydrated mineral reflectance spectra ("F2-12"). These new filter sets, along with the Beagle 2 filter set (currently the baseline for the ExoMars PanCam), were tested on their ability to identify hydrated minerals and biosignatures present in Mars analog rocks. The filter sets, with varying degrees of ability, detected the spectral features of minerals jarosite, opaline silica, alunite, nontronite, and siderite present in these rock samples. None of the filter sets, however, were able to detect fossilized biomat structures and small (<2?mm) mineralogical heterogeneities present in silica sinters. Both new filter sets outperformed the Beagle 2 filters, with F2-12 detecting the most spectral features produced by hydrated minerals and providing the best discrimination between samples. Future work involving more extensive testing on Mars analog samples that exhibit a wider range of mineralogies would be the next step in carefully evaluating the new filter sets. 相似文献
824.
825.
Based on the multipoint magnetic observations of Cluster from 2001 to 2004, the magnetic field structure in magnetotail Neutral Sheet (NS) is statistically surveyed. The results are as follows. In NS, a cubic function is selected to reveal the relation between y (GSM) and positional parameter z. The relation between y and magnetic field values indicates that the magnetic field is weak at midnight region and strengthens gradually at the duskside and dawnside. The relation between y and curvature radius is expressed by a quadratic function. And Rc of flattened CS is less than that of the normal CS. By determines the orientation of MFLs' configuration. The polar angle of the curvature vector is affected by the NS configuration. In addition, the correlation between the polar angle of the curvature vector and z is higher. The polar angle of the normal of the osculating plane is uncertain in the center area. The relation between the azimuthal angles of the curvature vector (the normal of the osculating plane) and y is negatively correlated. An empirical model applied to yz plane of the three-dimensional structure of the magnetic field lines in the NS are developed, and it is represented as a function of the positional parameter y. Finally, the current density is also statistically surveyed. 相似文献
826.
The implications of the STS-107 tragedy on weightlessness research in the NASA program are reviewed. 相似文献
827.
Life and its former traces can only be detected from space when they are abundant and exposed to the planetary atmosphere at the moment of investigation by orbiters. Exposed rock surfaces present a multifractal labyrinth of niches for microbial life. Based upon our studies of highly stress-resistant microcolonial fungi of stone monument and desert rock surfaces, we propose that microbial biofilms that develop and become preserved on rock surfaces can be identified remotely by the following characteristics: (1) the existence of spectroscopically identifiable compounds that display unique adsorption, diffraction, and reflection patterns characteristic of biogenerated organic compounds (e.g., chlorophylls, carotenes, melanins, and possibly mycosporines), (2) demonstrably biogenic geomorphological features (e.g., biopitting, biochipping, and bioexfoliation), and (3) biominerals produced in association with biofilms that occupy rock surfaces (e.g., oxalates, forsterite, and special types of carbonates, sulfides, and silicates). Such traces or biosignatures of former life could provide macroscopically visible morphotypes and chemically identifiable products uniquely indicative of life. 相似文献
828.
在开发和制造“联合攻击战斗机”(JSF)的项目竞争中,英国航宇工业公司(BAe)宣布加入由洛克希德·马丁公司领导的研制组。这一决定必将促使两公司之间发展更深一步的战略联盟关系。来自这两家公司的官员称BAe将参加这个最终价值近1000亿美元的JSF项目的所有阶段。洛克希德·马丁公司和波音公司正分别领导着两个互相竞争的JSF研制组。这两个组去年都得到了概念验证阶段合同。每个组都要设计和制造两架原型机。到2001年美国国防部将从中选定 相似文献
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830.