Characterization and Calibration of the CheMin Mineralogical Instrument on Mars Science Laboratory

A principal goal of the Mars Science Laboratory (MSL) rover Curiosity is to identify and characterize past habitable environments on Mars. Determination of the mineralogical and chemical composition of Martian rocks and soils constrains their formation and alteration pathways, providing information on climate and habitability through time. The CheMin X-ray diffraction (XRD) and X-ray fluorescence (XRF) instrument on MSL will return accurate mineralogical identifications and quantitative phase abundances for scooped soil samples and drilled rock powders collected at Gale Crater during Curiosity’s 1-Mars-year nominal mission. The instrument has a Co X-ray source and a cooled charge-coupled device (CCD) detector arranged in transmission geometry with the sample. CheMin’s angular range of 5^° to 50^° 2θ with <0.35^° 2θ resolution is sufficient to identify and quantify virtually all minerals. CheMin’s XRF requirement was descoped for technical and budgetary reasons. However, X-ray energy discrimination is still required to separate Co?Kα from Co?Kβ and Fe?Kα photons. The X-ray energy-dispersive histograms (EDH) returned along with XRD for instrument evaluation should be useful in identifying elements Z>13 that are contained in the sample. The CheMin XRD is equipped with internal chemical and mineralogical standards and 27 reusable sample cells with either Mylar^? or Kapton^? windows to accommodate acidic-to-basic environmental conditions. The CheMin flight model (FM) instrument will be calibrated utilizing analyses of common samples against a demonstration-model (DM) instrument and CheMin-like laboratory instruments. The samples include phyllosilicate and sulfate minerals that are expected at Gale crater on the basis of remote sensing observations.     

Subsurface filamentous fabrics: an evaluation of origins based on morphological and geochemical criteria, with implications for exopaleontology

The fossil record of the subsurface biosphere is sparse. Results obtained on subsurface filamentous fabrics (SFF) from >225 paleosubsurface sites in volcanics, oxidized ores, and paleokarst of subrecent to Proterozoic age are presented. SFF are mineral encrustations on filamentous or fibrous substrates that formed in subsurface environments. SFF occur in association with low-temperature aqueous mineral assemblages and consist of tubular, micron-thick (median 1.6 micron) filaments in high spatial density, which occur as irregular masses, matted fabrics, and vertically draped features that resemble stalactites. Micron-sized filamentous centers rule out a stalactitic origin. Morphometric analysis of SFF filamentous forms demonstrates that their shape more closely resembles microbial filaments than fibrous minerals. Abiogenic filament-like forms are considered unlikely precursors of most SFF, because abiogenic forms differ in the distribution of widths and have a lower degree of curvature and a lower number of direction changes. Elemental analyses of SFF show depletion in immobile elements (e.g., Al, Th) and a systematic enrichment in As and Sb, which demonstrates a relation to environments with high flows of water. Sulfur isotopic analyses are consistent with a biological origin of a SFF sample from a Mississippi Valley-Type deposit, which is consistent with data in the literature. Fe isotopes in SFF and active analogue systems, however, allow no discrimination between biogenic and abiogenic origins. The origin of most SFF is explained as permineralized remains of microbial filaments that possibly record rapid growth during phases of high water flow that released chemical energy. It is possible that some SFF formed due to encrustation of mineral fibers. SFF share similarities with Microcodium from soil environments. SFF are a logical target in the search for past life on Mars. The macroscopic nature of many SFF allows for their relatively easy in situ recognition and targeting for more detailed microstructural and geochemical analysis.     

Effects of DC and AC electric and magnetic fields on people andanimals

The calculation of field intensity is briefly reviewed. The effects of DC fields and fields from 60-Hz and three-phase power lines are discussed. Measurement of the field under a 12-kV distribution line is described. The insignificant nature of most exposure is emphasized     

The NASA Astrobiology Roadmap

The NASA Astrobiology Roadmap provides guidance for research and technology development across the NASA enterprises that encompass the space, Earth, and biological sciences. The ongoing development of astrobiology roadmaps embodies the contributions of diverse scientists and technologists from government, universities, and private institutions. The Roadmap addresses three basic questions: how does life begin and evolve, does life exist elsewhere in the universe, and what is the future of life on Earth and beyond? Seven Science Goals outline the following key domains of investigation: understanding the nature and distribution of habitable environments in the universe, exploring for habitable environments and life in our own Solar System, understanding the emergence of life, determining how early life on Earth interacted and evolved with its changing environment, understanding the evolutionary mechanisms and environmental limits of life, determining the principles that will shape life in the future, and recognizing signatures of life on other worlds and on early Earth. For each of these goals, Science Objectives outline more specific high priority efforts for the next three to five years. These eighteen objectives are being integrated with NASA strategic planning.     

Morphological biosignatures and the search for life on Mars

This report provides a rationale for the advances in instrumentation and understanding needed to assess claims of ancient and extraterrestrial life made on the basis of morphological biosignatures. Morphological biosignatures consist of bona fide microbial fossils as well as microbially influenced sedimentary structures. To be recognized as evidence of life, microbial fossils must contain chemical and structural attributes uniquely indicative of microbial cells or cellular or extracellular processes. When combined with various research strategies, high-resolution instruments can reveal such attributes and elucidate how morphological fossils form and become altered, thereby improving the ability to recognize them in the geological record on Earth or other planets. Also, before fossilized microbially influenced sedimentary structures can provide evidence of life, criteria to distinguish their biogenic from non-biogenic attributes must be established. This topic can be advanced by developing process-based models. A database of images and spectroscopic data that distinguish the suite of bona fide morphological biosignatures from their abiotic mimics will avoid detection of false-positives for life. The use of high-resolution imaging and spectroscopic instruments, in conjunction with an improved knowledge base of the attributes that demonstrate life, will maximize our ability to recognize and assess the biogenicity of extraterrestrial and ancient terrestrial life.     

The NASA Astrobiology Roadmap

The NASA Astrobiology Roadmap provides guidance for research and technology development across the NASA enterprises that encompass the space, Earth, and biological sciences. The ongoing development of astrobiology roadmaps embodies the contributions of diverse scientists and technologists from government, universities, and private institutions. The Roadmap addresses three basic questions: How does life begin and evolve, does life exist elsewhere in the universe, and what is the future of life on Earth and beyond? Seven Science Goals outline the following key domains of investigation: understanding the nature and distribution of habitable environments in the universe, exploring for habitable environments and life in our own solar system, understanding the emergence of life, determining how early life on Earth interacted and evolved with its changing environment, understanding the evolutionary mechanisms and environmental limits of life, determining the principles that will shape life in the future, and recognizing signatures of life on other worlds and on early Earth. For each of these goals, Science Objectives outline more specific high-priority efforts for the next 3-5 years. These 18 objectives are being integrated with NASA strategic planning.     

The formation of sulfate and elemental sulfur aerosols under varying laboratory conditions: implications for early earth

The presence of sulfur mass-independent fractionation (S-MIF) in sediments more than 2.45?×?10(9) years old is thought to be evidence for an early anoxic atmosphere. Photolysis of sulfur dioxide (SO(2)) by UV light with λ?相似文献   

Gypsum-permineralized microfossils and their relevance to the search for life on Mars

Abstract Orbital and in situ analyses establish that aerially extensive deposits of evaporitic sulfates, including gypsum, are present on the surface of Mars. Although comparable gypsiferous sediments on Earth have been largely ignored by paleontologists, we here report the finding of diverse fossil microscopic organisms permineralized in bottom-nucleated gypsums of seven deposits: two from the Permian (～260?Ma) of New Mexico, USA; one from the Miocene (～6?Ma) of Italy; and four from Recent lacustrine and saltern deposits of Australia, Mexico, and Peru. In addition to presenting the first report of the widespread occurrence of microscopic fossils in bottom-nucleated primary gypsum, we show the striking morphological similarity of the majority of the benthic filamentous fossils of these units to the microorganisms of a modern sulfuretum biocoenose. Based on such similarity, in morphology as well as habitat, these findings suggest that anaerobic sulfur-metabolizing microbial assemblages have changed relatively little over hundreds of millions of years. Their discovery as fossilized components of the seven gypsiferous units reported suggests that primary bottom-nucleated gypsum represents a promising target in the search for evidence of past life on Mars. Key Words: Confocal laser scanning microscopy-Gypsum fossils-Mars sample return missions-Raman spectroscopy-Sample Analysis at Mars (SAM) instrument-Sulfuretum. Astrobiology 12, 619-633.