Cosmic rays represent one of the most fascinating research themes in modern astronomy and physics. Significant progress is being made toward an understanding of the astrophysics of the sources of cosmic rays and the physics of interactions in the ultrahigh-energy range. This is possible because several new experiments in these areas have been initiated. Cosmic rays may hold answers to a great number of fundamental questions, but they also shape our natural habitat and influence the radiation environment of our planet Earth. The importance of the study of cosmic rays has been acknowledged in many fields, including space weather science and astrobiology.

Continue reading "Cosmic Rays: A Review for Astrobiologists" »

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A central question of astrobiology concerns the origin and distribution of life in the Universe. For this reason, astrobiology can be considered to fall within the science called transitional biology. If we accept that life originated by a process of prebiotic chemical evolution, the next question concerns the nature of the transitional pathway from inanimate chemical systems to the first forms of life on Earth. These possible transitional states are the subject matter of transitional biology as a discipline.

Continue reading "Why Is the Definition of Life So Elusive? Epistemological Considerations" »

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The importance of hypersaline environments over geological time, the discovery of similar habitats on Mars, and the importance of methane as a biosignature gas combine to compel an understanding of the factors important in controlling methane released from hypersaline microbial mat environments. To further this understanding, changes in stable carbon isotopes of methane and possible methanogenic substrates in microbial mat communities were investigated as a function of salinity here on Earth. Microbial mats were sampled from four different field sites located within salterns in Baja California Sur, Mexico. Salinities ranged from 50 to 106 parts per thousand (ppt).

Continue reading "Isotopic Composition of Methane and Inferred Methanogenic Substrates Along a Salinity Gradient in a Hypersaline Microbial Mat System" »

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Once it was established that the spaceflight environment was not a drastic impediment to plant growth, a remaining space biology question was whether long-term spaceflight exposure could cause changes in subsequent generations, even if they were returned to a normal Earth environment. In this study, we used a genomic approach to address this question. We tested whether changes in gene expression patterns occur in wheat plants that are several generations removed from growth in space, compared to wheat plants with no spaceflight exposure in their lineage. Wheat flown on Mir for 167 days in 1991 formed viable seeds back on Earth.

Continue reading "Effects of a Spaceflight Environment on Heritable Changes in Wheat Gene Expression" »

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We have used the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) high-energy gamma-ray detector to look for fast blue-green laser pulses from the vicinity of 187 stars. The STACEE detector offers unprecedented light-collecting capability for the detection of nanosecond pulses from such lasers. We estimate STACEE's sensitivity to be approximately 10photons/m2 at a wavelength of 420nm.

Continue reading "OSETI with STACEE: A Search for Nanosecond Optical Transients from Nearby Stars" »

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With the assumption that future attempts to explore our Solar System for life will be limited by economic constraints, we have formulated a series of principles to guide future searches: (1) the discovery of life that has originated independently of our own would have greater significance than evidence for panspermia; (2) an unambiguous identification of living beings (or the fully preserved, intact remains of such beings) is more desirable than the discovery of markers or fossils that would inform us of the presence of life but not its composition; (3) we should initially seek carbon-based life that employs a set of monomers and polymers substantially different than our own, which would effectively balance the need for ease of detection with that of establishing a separate origin; (4) a "follow-the-carbon" strategy appears optimal for locating such alternative carbon-based life.

Continue reading "The Search for Alien Life in Our Solar System: Strategies and Priorities" »

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Geological and biological evidence suggests that Earth was warm during most of its early history, despite the fainter young Sun. Upper bounds on the atmospheric CO2 concentration in the Late Archean/Paleoproterozoic (2.8–2.2 Ga) from paleosol data suggest that additional greenhouse gases must have been present.

Continue reading "A Revised, Hazy Methane Greenhouse for the Archean Earth" »

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Availability of reduced nitrogen is considered a prerequisite for the genesis of life from prebiotic precursors. Most atmospheric and oceanic models for the Hadean Earth predict a mildly oxidizing environment that is conducive to the formation and stability of only oxidized forms of nitrogen.

Continue reading "Inorganic Nitrogen Reduction and Stability under Simulated Hydrothermal Conditions" »

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Based on new image data from the High Resolution Imaging Science Experiment (HiRISE) on Mars Reconnaissance Orbiter (MRO), a case can be made that several structures in Vernal Crater, Arabia Terra are ancient springs. This interpretation is based on comprehensive geomorphologic analysis coupled with assessment of multiple hypotheses.

Continue reading "A Case for Ancient Springs in Arabia Terra, Mars" »

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Liquid water is essential to life as we know it on Earth; therefore, the search for water on Mars is a critical component of the search for life. Olivine, a mineral identified as present on Mars, has been proposed as an indicator of the duration and characteristics of water because it dissolves quickly, particularly under low-pH conditions. The duration of olivine persistence relative to glass under conditions of aqueous alteration reflects the pH and temperature of the reacting fluids.

Continue reading "Short- and Long-Term Olivine Weathering in Svalbard: Implications for Mars" »

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This study identifies transcriptional regulation of stress response element (STRE) genes in space in the model eukaryotic organism, Saccharomyces cerevisiae. To determine transcription-factor dependence, gene expression changes in space were examined in strains bearing green fluorescent protein–tagged (GFP-tagged) reporters for YIL052C (Sfp1 dependent with stress), YST-2 (Sfp1/Rap1 dependent with stress), or SSA4 (Msn4 dependent with stress), along with strains of SSA4-GFP and YIL052C-GFP with individual deletions of the Msn4 or Sfp1.

Continue reading "Novel Sfp1 Transcriptional Regulation of Saccharomyces cerevisiae Gene Expression Changes During Spaceflight" »

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Chirality is an excellent indicator of life, but naturally occurring astrobiological (as well as terrestrial) samples nearly always exhibit massive depolarizing light scattering, which renders conventional polarimeters useless. For astrobiological applications, we instead consider a novel polarimeter originally developed for non-invasive human-glucose measurement. It involves deliberately rotating in time the plane of polarization of a linearly polarized beam and detecting the shift in the plane of the rotating linearly polarized component of the transmitted light from a chiral sample relative to the input polarization plane. We find that this polarimeter can operate in 3 orders of magnitude more depolarizing scattering than conventional polarimeters. Furthermore, it can also be designed to be lightweight, compact, and energy efficient.

Astrobiology. December 2008, 8(6): 1061-1069.

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0151

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Astrobiology. October 2008, 8(5): 1001-1011.
http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0142

We report on the design, operation, and data analysis methods employed on the VNIR imaging spectrometer instrument that was part of the Mars Astrobiology Research and Technology Experiment (MARTE). The imaging spectrometer is a hyperspectral scanning pushbroom device sensitive to VNIR wavelengths from 400-1000 nm. During the MARTE project, the spectrometer was deployed to the Rio Tinto region of Spain. We analyzed subsets of three cores from Rio Tinto using a new band modeling technique. We found most of the MARTE drill cores to contain predominantly goethite, though spatially coherent areas of hematite were identified in Core 23. We also distinguished non Fe-bearing minerals that were subsequently analyzed by X-ray diffraction (XRD) and found to be primarily muscovite. We present drill core maps that include spectra of goethite, hematite, and non Fe-bearing minerals. Astrobiology 8, 1001-1011.

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Astrobiology. October 2008, 8(5): 1013-1021.
http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2006.0107

The 2005 Mars Astrobiology Research and Technology Experiment (MARTE) project conducted a simulated 1-month Mars drilling mission in the Rio Tinto district, Spain. Dry robotic drilling, core sampling, and biological and geological analytical technologies were collectively tested for the first time for potential use on Mars. Drilling and subsurface sampling and analytical technologies are being explored for Mars because the subsurface is the most likely place to find life on Mars. The objectives of this work are to describe drilling, sampling, and analytical procedures; present the geological analysis of core and borehole material; and examine lessons learned from the drilling simulation.

Continue reading "The Subsurface Geology of Rio Tinto: Material Examined During a Simulated Mars Drilling Mission for the Mars Astrobiology Research and Technology Experiment (MARTE)" »

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Astrobiology. October 2008, 8(5): 1049-1060.
http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0146

Sampling of subsurface rock may be required to detect evidence of past biological activity on Mars. The Mars Astrobiology Research and Technology Experiment (MARTE) utilized the Rio Tinto region, Spain, as a Mars analog site to test dry drilling technologies specific to Mars that retrieve subsurface rock for biological analysis. This work examines the usefulness of visible-near infrared (VNIR) (450-1000 nm) point spectrometry to characterize ferric iron minerals in core material retrieved during a simulated Mars drilling mission. VNIR spectrometry can indicate the presence of aqueously precipitated ferric iron minerals and, thus, determine whether biological analysis of retrieved rock is warranted. Core spectra obtained during the mission with T1 (893-897 nm) and T2 (644-652 nm) features indicate goethite-dominated samples, while relatively lower wavelength T1 (832-880 nm) features indicate hematite. Hematite/goethite molar ratios varied from 0 to 1.4, and within the 880-898 nm range, T1 features were used to estimate hematite/goethite molar ratios. Post-mission X-ray analysis detected phyllosilicates, which indicates that examining beyond the VNIR (e.g., shortwave infrared, 1000-2500 nm) will enhance the detection of other minerals formed by aqueous processes.

Continue reading "Visible-Near Infrared Point Spectrometry of Drill Core Samples from Rio Tinto, Spain: Results from the 2005 Mars Astrobiology Research and Technology Experiment (MARTE) Drilling Exercise" »

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Astrobiology. October 2008, 8(5): 1023-1047.
http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2006.0104

A search for evidence of cryptic life in the subsurface region of a fractured Paleozoic volcanosedimentary deposit near the source waters of the Rio Tinto River (Iberian pyrite belt, southwest Spain) was carried out by Mars Astrobiology Research and Technology Experiment (MARTE) project investigators in 2003 and 2004. This conventional deep-drilling experiment is referred to as the MARTE ground truth drilling project. Boreholes were drilled at three sites, and samples from extracted cores were analyzed with light microscopy, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy. Core leachates were analyzed with ion chromatography, and borehole fluids were analyzed with ion and gas chromatography. Key variables of the groundwater system (e.g., pO2, pH, and salinity) exhibit huge ranges probably due to surficial oxygenation of overall reducing waters, physical mixing of waters, and biologically mediated water-rock interactions.

Continue reading "Underground Habitats in the Rio Tinto Basin: A Model for Subsurface Life Habitats on Mars" »

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Santa Clara, California, April 14–17, 2008

The 5th Astrobiology Science Conference (AbSciCon08), hosted by the SETI Institute, brings together a community of scholars, students, and educators that is as vigorous and intellectually diverse as ever. These qualities are reflected in the content of this volume, which includes 647 abstracts involving 1,683 authors from 28 countries. These abstracts are organized into 38 topical sessions and 6 plenary sessions that were developed around the three major themes of the conference: the astrophysical and planetary context for life; the origin and evolution of life; and the search for life in our Solar System and beyond. An astounding range of subjects is covered--from prebiotic chemistry to cosmology, with stops at virology, Precambrian geochemistry, and Mars exploration, among other subjects, along the way. Presenta- tions on engaging students, teachers, and the public in astrobiology thread throughout the conference, reflecting its broad appeal. Clearly, the community is healthy and poised for a vibrant future!

Continue reading "The Astrobiology Science Conference, 2008" »

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Astrobiology December 2007, 7(6): 819-823

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0207

A key challenge in Astrobiology is to comprehend life and its interaction with the environment at a level sufficiently fundamental to embrace the alternative biochemistries that may be encountered in a search for life elsewhere (Baross et al., 2007).

Continue reading "A "Follow the Energy" Approach for Astrobiology" »

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Astrobiology December 2007, 7(6): 1023-1032

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2006.0091

The shallow habitable region of cratonal crust deforms with a strain rate on the order of 1019 s1. This is rapid enough that small seismic events are expected on one-kilometer spatial scales and one-million-year timescales. Rock faulting has the potential to release batches of biological substrate, such as dissolved H2, permitting transient blooms.

Continue reading "Did Earthquakes Keep the Early Crust Habitable?" »

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Astrobiology December 2007, 7(6): 1006-1022

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0156

Europa is a prime target for astrobiology. The presence of a global subsurface liquid water ocean and a composition likely to contain a suite of biogenic elements make it a compelling world in the search for a second origin of life. Critical to these factors, however, may be the availability of energy for biological processes on Europa.

Continue reading "Energy, Chemical Disequilibrium, and Geological Constraints on Europa" »

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Astrobiology December 2007, 7(6): 987-1005

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0075

We examine means for driving hydrothermal activity in extraterrestrial oceans on planets and satellites of less than one Earth mass, with implications for sustaining a low level of biological activity over geological timescales. Assuming ocean planets have olivine-dominated lithospheres, a model for cooling-induced thermal cracking shows how variation in planet size and internal thermal energy may drive variation in the dominant type of hydrothermal system--for example, high or low temperature system or chemically driven system.

Continue reading "Hydrothermal Systems in Small Ocean Planets" »

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Astrobiology December 2007, 7(6): 971-986

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2006.0096

Dissolved H2 concentrations up to the mM range and H2 levels up to 9-58% by volume in the free gas phase are reported for groundwaters at sites in the Precambrian shields of Canada and Finland. Along with previously reported dissolved H2 concentrations up to 7.4 mM for groundwaters from the Witwatersrand Basin, South Africa, these findings indicate that deep Precambrian Shield fracture waters contain some of the highest levels of dissolved H2 ever reported and represent a potentially important energy-rich environment for subsurface microbial life. The

Continue reading "Hydrogeologic Controls on Episodic H2 Release from Precambrian Fractured Rocks--Energy for Deep Subsurface Life on Earth and Mars" »

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Astrobiology December 2007, 7(6): 951-970

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0150

Radiolysis of water may provide a continuous flux of an electron donor (molecular hydrogen) to subsurface microbial communities. We assessed the significance of this process in anoxic marine sediments by comparing calculated radiolytic H2 production rates to estimates of net (organic-fueled) respiration at several Ocean Drilling Program (ODP) Leg 201 sites. Radiolytic H2 yield calculations are based on abundances of radioactive elements (uranium, thorium, and potassium), porosity, grain density, and a model of water radiolysis. Net respiration estimates are based on fluxes of dissolved electron acceptors and their products. Comparison of radiolytic H2 yields and respiration at multiple sites suggests that radiolysis gains importance as an electron donor source as net respiration and organic carbon content decrease.

Continue reading "Radiolytic Hydrogen and Microbial Respiration in Subsurface Sediments" »

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Astrobiology December 2007, 7(6): 933-950

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2006.0119

Numerical models are employed to investigate sources of chemical energy for autotrophic microbial metabolism that develop during mixing of oxidized seawater with strongly reduced fluids discharged from ultramafic-hosted hydrothermal systems on the seafloor. Hydrothermal fluids in these systems are highly enriched in H2 and CH4 as a result of alteration of ultramafic rocks (serpentinization) in the subsurface. Based on the availability of chemical energy sources, inferences are made about the likely metabolic diversity, relative abundance, and spatial distribution of microorganisms within ultramafic-hosted systems.

Continue reading "Geochemical Constraints on Sources of Metabolic Energy for Chemolithoautotrophy in Ultramafic-Hosted Deep-Sea Hydrothermal Systems" »

Posted by Keith Cowing at 9:43 AM | Permalink | Comments (0)

Astrobiology December 2007, 7(6): 905-932

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0128

In June 2003, the geochemical composition of geothermal fluids was determined at 9 sites in the Vulcano hydrothermal system, including sediment seeps, geothermal wells, and submarine vents. Compositional data were combined with standard state reaction properties to determine the overall Gibbs free energy (

Continue reading "Temporal Changes in Fluid Chemistry and Energy Profiles in the Vulcano Island Hydrothermal System" »

Posted by Keith Cowing at 9:42 AM | Permalink | Comments (0)

Astrobiology December 2007, 7(6): 891-904

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2006.0118

The common thread of energy release suggests that diverse microbial metabolic processes can be compared through thermodynamic analyses. The resulting energy and power requirements can provide quantitative constraints on habitability. Because previous thermodynamic analyses have focused on the minimum amount of energy needed for the growth of a microorganism or community, the focus of this study is to gain a fuller understanding of the microbial response to highly habitable conditions.

Continue reading "A Thermodynamic Analysis of Microbial Growth Experiments" »

Posted by Keith Cowing at 9:42 AM | Permalink | Comments (0)

Astrobiology December 2007, 7(6): 873-890

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0127

Formate, a simple organic acid known to support chemotrophic hyperthermophiles, is found in hot springs of varying temperature and pH. However, it is not yet known how metabolic strategies that use formate could contribute to primary productivity in hydrothermal ecosystems. In an effort to provide a quantitative framework for assessing the role of formate metabolism, concentration data for dissolved formate and many other solutes in samples from Yellowstone hot springs were used, together with data for coexisting gas compositions, to evaluate the overall Gibbs energy for many reactions involving formate oxidation or reduction.

Continue reading "Formate as an Energy Source for Microbial Metabolism in Chemosynthetic Zones of Hydrothermal Ecosystems" »

Posted by Keith Cowing at 9:41 AM | Permalink | Comments (0)

Astrobiology December 2007, 7(6): 852-872

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2006.0066

There are growing indications that life began in a radioactive beach environment. A geologic framework for the origin or support of life in a Hadean heavy mineral placer beach has been developed, based on the unique chemical properties of the lower-electronic actinides, which act as nuclear fissile and fertile fuels, radiolytic energy sources, oligomer catalysts, and coordinating ions (along with mineralogically associated lanthanides) for prototypical prebiotic homonuclear and dinuclear metalloenzymes.

Continue reading "Actinides and Life's Origins" »

Posted by Keith Cowing at 9:40 AM | Permalink | Comments (0)

Astrobiology December 2007, 7(6): 839-851

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0137 A framework is proposed for a quantitative approach to studying habitability. Considerations of environmental supply and organismal demand of energy lead to the conclusions that power units are most appropriate and that the units for habitability become watts per organism.

Continue reading "Quantitative Habitability" »

Posted by Keith Cowing at 9:39 AM | Permalink | Comments (0)

Astrobiology December 2007, 7(6): 824-838

http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2006.0095

Habitability can be formulated as a balance between the biological demand for energy and the corresponding potential for meeting that demand by transduction of energy from the environment into biological process. The biological demand for energy is manifest in two requirements, analogous to the voltage and power requirements of an electrical device, which must both be met if life is to be supported.

Continue reading "An Energy Balance Concept for Habitability" »

Posted by Keith Cowing at 9:38 AM | Permalink | Comments (0)