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Executive Summary

The Ames team pursued complementary lines of research on the development of habitable planetary environments, the origins of biological functions, the biosignatures created by microbial ecosystems fueled by light or by chemical energy, and the survival of life in space and in changing environments on Earth. These investigations broadly address NASA’s Astrobiology Roadmap. Their direct involvement in multiple NASA missions provides context, motivation, and collaborative opportunities for our research, and education and public outreach efforts. Please visit www.amesteam.arc.nasa.gov.

Ames team astrophysicists continued to investigate the formation of habitable planetary systems with a focus on key processes in protoplanetary disks. It had been proposed that the lifetimes of planet-forming disks might attain a maximum for central star masses of order 1 to 3 solar masses. It was found that there is no such maximum but rather that stars in the range 0.3 to 3 solar masses have disks with similar lifetimes (1 to 2 Myr) against photoevaporation. Habitable planets do have time to form around stars less massive than 3 solar masses but they are unlikely to form around more massive stars. In another study, we found that various infrared lines probe the density, temperature, and chemical abundances of gas at various distances from the central star. Spectral lines that probe the terrestrial planet region around 1 AU include the pure rotational lines of H₂, H₂O, and OH, the ground state vibrational lines of CO and H₂O, and the fine structure lines of [FeI], [FeII], [SiII], [OI], [NeII], [NeIII], [ArII] and [SI]. Lines probing the 100 AU region of the outer disk include low J rotational transitions of CO, and the fine structure lines of [CII] and [OI]. One key conclusion is that the [NeII] emission line is currently the most sensitive way to detect gas in the planet-forming region of a young star.

The team continued to model large-scale transport in protoplanetary disks and has improved its numerical schemes to describe accurately the turbulent diffusion and meridional advection as well as the chemical reactions. We also have developed models for optical scattering by astrophysical dust grains and we reported new findings concerning the spatial distribution of oxygen isotopes in the protoplanetary nebula.

Team members refined the Systemic Console, a flexible Graphic User Interface-based computational tool for analyzing radial velocity and transit data for extrasolar planetary systems. The software code base has been completed, and it is fully operational and available for downloading at www.oklo.org. We also investigated the formation and detectability of the potentially habitable terrestrial planets orbiting Alpha Centauri B.

Team astrochemists traced the formation and evolution of compounds in space, with particular emphasis on 1) identifying compounds that are relevant for prebiotic chemistry and 2) understanding their possible roles in origins of life. We incorporated our world unique collection of >800 mid-IR spectra of polycyclic aromatic hydrocarbons (PAHs) into a database, which is nearly complete. This is the collection upon which the interstellar PAH model is based. The database/web user interface should be ready for launch in March 2009 and it will revolutionize how cosmic spectra are analyzed. We published isotopic experiments showing that the production of amino acids in astrophysical ices is complex and does not follow the pathways predicted by either Strecker synthesis or radical interaction models. We published a review of prebiotic chemical evolution as part of the American Chemical Society’s series on Chemical Education. We contributed to the publication of findings that cometary organics in samples returned by the Stardust mission are richer in oxygen and nitrogen than meteoritic organics and they also contain volatile materials not observed in meteorites. Some organics are enriched in D and ¹⁵N, implying an interstellar/presolar chemical heritage.

Team molecular biologists investigated the evolutionary origins of functional macromolecules using both experimental and computational approaches. We continued to study the first enzyme with novel function that we had selected through in vitro evolution. This enzyme joins two fragments of RNA into a single strand (it acts as an RNA ligase). We enhanced the stability of this enzyme at higher temperatures in order to obtain a more compact structure and increase enzymatic activity. Four clones assayed at 65°C all showed ligation activity whereas the ligases resulting from the original selection, assayed under the same conditions, yielded no detectable ligation products. All four heat-evolved ligases also showed increased activities at room temperature compared to the original ligases. The results demonstrate the evolutionary potential of simple proteins to increase both their stability and enzymatic activity.

Team members used computer design approach to redesign our novel lab-evolved protein that binds adenosine triphosphate such that it can bind another, closely related molecule, guanosine triphosphate. This required extending one loop in this protein such that it could form sequence-dependent hydrogen bonds capable of favorable interactions with either adenine or guanine. These studies provide clues to identifying selection criteria in protobiological evolution. “Evolutionary pruning” would have eliminated any proteins lacking sufficient evolutionary flexibility either to improve their catalytic efficiency or to alter their substrate specificity in response to a small number of mutations.

Team biogeochemists examined the production by microbial ecosystems of “biosignatures,” which are chemical or physical features or patterns that can only be formed by biological processes. In photosynthetic (light-harvesting) microbial mats, we examined the factors that control the formation of biosignature gases, such as could be seen by telescope in the atmospheres of planets orbiting other stars, and isotopic and morphological features that could be preserved in the rock record, such as could be examined by rovers on Mars. We also studied the formation of morphological and mineral signatures in chemotrophic (chemically fueled) ecosystems that have no direct access to either light or the products of photosynthesis. Chemotrophic systems are viable possibilities for extant life on modern day Mars or Europa.

The team just completed a year-long incubation experiment to examine the effects of variable sulfate levels (including Archaean ocean levels) on sulfide isotopes as signatures of sulfur cycling in photosynthetic microbial mats. This work will characterize a broader range of sulfur isotopes and sulfur species at considerably finer spatial resolution than has thus far been achieved in comparable systems. We also examined the templating by biofilms of characteristic crystal morphologies during sulfate mineral formation; such templating also might have influenced the deposition of martian sulfates. Biofilms have imparted distinctive textures and induce unique crystallographic aspect ratios, such as enlarged {110} prisms and shortening on the [001] axis, during gypsum mineral formation. Biologically induced native sulfur, calcium carbonate and celestite were observed in syngenetic and replacive relationships with gypsum.

Team members continued to characterize the energetic dimension of habitability as specifically applicable to water-rock reactions in the terrestrial and martian subsurface. We are developing a theoretical energy balance concept of habitability to provide a framework for quantifying habitability, as volumetrically or areally normalized biomass density, as a function of physical and chemical environments. We are applying this concept to characterize and quantify habitability in the context of the robotic exploration of Mars. We participated in the Carnegie-led Arctic Mars Analog Svalbard Expedition (AMASE) to assess habitability using Mars Science Laboratory (MSL) mission flight instrumentation in Mars-analog settings. Our findings have appeared in the journal Astrobiology.

Team biogeochemists refined their numerical model to link microbial mats to global biosphere processes in order to reflect more details of the carbon cycles. The model now simulates photorespiration and the excretion of sugars by cyanobacteria when mat porewaters are supersaturated in O₂. When mat porewaters become anoxic after sundown, the cyanobacteria ferment these sugars. We added a cyanobacterial fermentation function using the photorespiration exudates as a substrate. The new source of carbon and energy changes the maximum simulated rate of bacterial sulfate reduction (BSR). In the original BSR model, photosynthesis supplied these exudates directly and thus the BSR rate was greatest at midday; now it occurs at night.

Team radiation biologists assessed the potential for life to move beyond Earth and survive in potentially lethal radiation environments. We obtained funding through the Announcement of Opportunity for Externally Mounted Payloads (SP-1201) to extend and refine our earlier studies of the survival in space of two halophiles, a Synechococcus cyanobacterium and Halorubrum chaoviatoris. We conducted verification tests at the Deutsches Zentrum für Luft- und Raumfahrt, Germany to determine compatibility between organisms and spacecraft experimental hardware. We participated in several high altitude balloon launches and verified that the total amount of radiation received over the duration of the flight was 0.9 mRem, well above the ground controls. Environmental radiation in balloons at altitude has a considerable effect on bacteria as compared to ground controls.

Team Earth scientists refined their model to assess South American land ecosystems with respect to the history of the carbon cycle in terms of Net Primary Production. To validate our assumptions on changes in Normalized Difference Vegetation Index, we explored the history of forcings of climate (volcanic, orbital, and solar) over the last 754 years. While the orbital and solar forcing could account for changes of a few calories in the solar energy at the surface of the Earth, the volcanic forcing produced a maximum cooling of sea surface temperature (SST), starting in 1453 when the Kuwae volcano erupted explosively in the New Hebrides and elevated non-marine sulfates to 1380 μg per liter of Antarctic ice. The aerosols of this eruption shaded the Earth and lowered the SST of the South Atlantic and the Western Pacific for several years. This and other volcanic eruptions have affected terrestrial vegetation of South America and hence the carbon cycle in the period 1246 to 2000.

Ames team members pursued diverse education and public outreach (EPO) activities that included efforts in high-impact public venues. Team members implemented a graduate-level astrobiology course at the University of California at Santa Cruz and an undergraduate astrobiology and space exploration course at Stanford University, and they participated in high-altitude balloon experiments launched through Stanford’s BioLaunch Program. These activities have contributed source material for the team’s EPO program. Team members gave numerous lab tours and demonstrations to scout troops and educators, they made presentations and lectures to K-12 classrooms, universities, museums, informal public venues, and more. Team members participated in National Public Radio interviews and were filmed for shows on the History Channel and for the National Geographic Society.

The team continued to forge its strong partnerships with Yellowstone National Park and Lassen Volcanic National Park by reinforcing the connections between microbiology and astrobiology. The hydrothermal features in these two national parks are key research targets for NASA’s astrobiology research program and they illustrate compelling aspects of astrobiology education and outreach. The team continued to collaborate with Yellowstone’s Division of Interpretation (DOI) to highlight astrobiology and microbiology by contributing content on astrobiology and thermal spring ecology for the online Old Faithful Virtual Visitor Center. Team members initiated a partnership with Lassen Volcanic National Park. They will engage high school students in the collection of thermal feature data for NASA astrobiologists. Documentation of these features by the student interns will provide a valuable database for future research. The team supported Lassen’s implementation during the upcoming school year of a Junior Park Astrobiology program for fifth through 12^th graders.

Team members collaborated with TERC, a not-for-profit education research and development organization, to present TERC’s Astrobiology high school science curriculum at national conferences, at Space Day, during Engineers Week, in individual classrooms and districts, and in Science Corps workshop formats at the University of Southern Maine. Ames had previously played a key role in developing this curriculum. During the upcoming school year the Maine Department of Education will conduct a classroom pilot study of Astrology in order to optimize its ultimate deployment in Maine classrooms.

The Ames team maintained its substantial presence in current and upcoming NASA missions. The P.I. is a strategic planning lead for the Mars Exploration Rover mission. A team Co-I is also P.I. of the CheMin X-ray diffraction spectrometer for the MSL mission. Other team members participate in the following ongoing or future missions: Kepler, Stardust, Stratospheric Observatory for Infrared Astronomy, Mars Reconnaissance Orbiter, MSL, and James Webb Space Telescope.