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" »

Posted by Keith Cowing at 9:47 AM | Permalink | Comments (0)

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" »

Posted by Keith Cowing at 9:45 AM | Permalink | Comments (0)

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" »

Posted by Keith Cowing at 9:44 AM | Permalink | Comments (0)

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.

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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" »

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