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Executive Summary

The Ames Research Center Team of the NASA Astrobiology Institute conducts complementary lines of research to understand the context for habitable environments and life, the origins of life and its impact on the planetary environment, and the future of life in changing environments. These investigations address all seven goals of NASA’s 2003 Astrobiology Roadmap and they pursue near-term roadmap objectives in ways that help to unify astrobiology and strengthen its linkages to flight missions. The Ames team conveys the content of its research program into its education and public outreach program through partnerships with NASA’s education programs, the California Academy of Sciences (CAS), Yellowstone National Park (YNP), New York Hall of Science, and several K-14 educational organizations. Strong conceptual and functional links to multiple NASA missions provide context, motivation, and resource-sharing opportunities for both the research and the education and public outreach efforts.

We investigated the processes that control the formation and the climates of planets. We are modeling the photoevaporation of protoplanetary disks around young stars. This year we constructed a numerical code that calculates the evaporation of disks around low mass (solar-type) stars caused by the ultraviolet and X-ray radiation field created by the young, low-mass, central stars themselves. We presented preliminary results of the heating, cooling, thermal structure, and emission spectra of disks derived from these models. We also presented the first estimates of mass loss rates and dispersal timescales for disks being evaporated by the ultraviolet and X-ray emission from their central stars. We reviewed mechanisms for dispersal of disks and described preliminary results on the photoevaporation caused by the central star.

We have nearly completed a public-domain software package, named “Systemic,” that analyzes radial velocity and photometric data for planetary systems. We will release an initial version to the www.transitsearch.org amateur astronomy community for beta testing. The focus of the initial test will be an attempt to obtain a better, self-consistent orbital model for the 55 Cancri 4 system and to test stability of the fit family. We have used Systemic to obtain a joint radial-velocity-photometric solution for the newly discovered transiting planet HD 149026b. The small transit radius of this Saturn-mass planet indicates that it has an extremely massive solid core (60-80 Earth Masses). This indicates that the core accretion hypothesis, and, by extension, the common formation of terrestrial planets, is almost certainly correct.

We developed a new cumulative-planetary-mass-model that predicts a surface density that is more consistent with planetary data than that obtained from the commonly used Hayashi minimum mass distribution. We investigated the condensation/sublimation front in the early solar system to determine the phase state (gas or ice) of important species related to organic chemical processes.

We completed preliminary 3D simulations of an Earth-like climate system that is subjected to extreme orbital configurations. We presented our results at the 2005 NAI meeting. We proposed that early Earth had an atmosphere with tens of percent H₂, and an H₂/CO₂ ratio greater than 1. Perhaps the early atmosphere was indeed a key source of organic molecules for prebiotic processes. We demonstrated that the biological record of extinction after the K-T event is consistent with the thermal pulse from the re-entering debris.

We are tracing, spectroscopically and chemically, the cosmic evolution of organic molecules from the interstellar medium to protoplanetary disks, planetesimals, and finally onto habitable bodies. We also examine the abiotic mechanisms of primitive membrane formation under the primordial conditions of a habitable planet. We have measured IR spectra of aromatic nitrogen heterocycles (a.k.a. polycyclic aromatic nitrogen heterocycles (PANHs) i.e., polycyclic aromatic hydrocarbons (PAHs) with N atoms) in solid H₂O at low temperature in the laboratory. We also measured mid- and near-IR and optical spectra of ionized PAHs in solid H₂O at various temperatures. We found the unexpected result that PAH ions are stable in cosmic ices at temperatures between 100 and 120 K, a very important regime for cosmic ices. We published IR lab spectra that help to interpret observations by NASA’s Spitzer Space telescope by showing that the new complex of emission features near 17 microns in many objects arises from various sizes and structures of PAHs. We observed that aromatics are more readily reduced during irradiation in solid ices than was previously thought, indicating that cyclic aliphatics might have a protostellar origin. A team member leads the proposal efforts for two astrobiology missions: ABE (Astrobiology Explorer) and ASPIRE (Astrobiology Space Infrared Explorer) which is now a mission concept study.

Our studies of potential prebiotic membranes have shown that the addition of aromatics to fatty acids cause changes in vesicle morphology corresponding to changes in surface tension measured on the Langmuir trough. We are also studying photochemical reactions that are facilitated by quinones that cross a bi-layer.

We are exploring the origin of metabolism in the earliest ancestors of cells by testing the hypothesis that proteins might have arisen and initially evolved in the absence of a genome. In order to generate laboratory models of protocellular protein catalysts, we have designed a novel, partially random protein library based on the DNA-binding domain of the human retinoid-X-receptor. We chose this domain because of its small size, stable fold, and two closely juxtaposed recognition loops. In the first selection, variants that specifically recognize adenosine triphosphate (ATP) were isolated. This work demonstrated that it is possible to significantly alter the function of a natural protein from DNA binding to ATP recognition while retaining the protein fold. In a second selection, we used the same library to isolate a novel protein that catalyzes a template-directed oligonucleotide ligation reaction. We continue to characterize our previously isolated ATP binding protein, which was obtained from a random sequence protein library. This protein exhibits a folding pattern not previously seen in biological proteins. Using nuclear magnetic resonance (NMR) spectroscopy, we showed that a new variant of this protein, which was selected for higher thermodynamic stability, retains the same overall structure.

We performed extensive computer simulation studies of model membrane peptides in order to explain the emergence of proteins that mediate transfer of ions, nutrients waste products and environmental signals across proto-cellular walls. We demonstrated that the insertion of α-helices into a membrane is energetically unfavorable, but that stability can be regained through their specific recognition and association into larger assemblies within the membrane. We further showed that, despite their simple structure, the emerging trans-membrane structures could possess properties that appear to require markedly larger complexity. These properties can be subtly modulated by local modifications to the sequence rather than global changes in molecular architecture. This is a convenient evolutionary solution because it does not require imposing conditions on the entire amino acid sequence.

We are characterizing the major factors that govern the formation of potentially diagnostic biosignatures in microbial ecosystems. We studied the microbial population structure and biogeochemical function of microbial mat communities by combining fieldwork in Baja, California, with detailed studies of live samples returned and maintained in a greenhouse facility. We employed a series of stable isotope-tracing experiments to construct detailed budgets of carbon flow through major chemical pools in the mats. We employed molecular biological techniques in situ to document systematic shifts in microbial population structure with changes in salinity. These studies help to interpret the biomarkers and likely community compositions of ancient sedimentary deposits hosted in evaporite sequences. They also might help us to interpret evaporitic systems on Mars. A team member published three studies that addressed the multiple roles that microorganisms play in creating biosignatures during carbonate sedimentation and lithification associated with the formation of stromatolites. Another member published a study of the effects of environmental stressors on photosynthetic microorganisms in geothermal springs of Yellowstone National Park.

We are extending the ecosystem-level studies of photosynthetic microbial mats to a planetary scale by refining and evaluating quantitative models that simulate energy relationships, biogeochemical cycling, trace gas exchange, and biodiversity in these systems. We published our first extensive computational model of elemental cycling in hypersaline microbial mats. Subsequently, we “added” to the model a guild of methanogens that rely on noncompetitive substrates such as trimethylamines for their methane metabolism. We also are better defining the roles of photorespiration and fermentation in the model. We have devised a method to model gas flux from the mat surface through the water and out into the atmosphere.

Co-I David Blake’s CheMin instrument was selected to fly on the Mars Science Laboratory (MSL) 2009 mission. This closely links our team’s work with the Mars program. CheMin will be deployed to study mineralogy in our field studies (ophiolite and Spitzbergen sites) so that our work can provide directly applicable context for interpretation of MSL science. We completed a mineralogical, geochemical, and microbial community analysis of Complexion Spring, California, which indicates extensive serpentization (with potential to support biology via hydrogen release). Team members continued studies of microbial activity associated with carbonate-cemented lava breccias from Spitzbergen, which are relevant analogs of some martian rocks. We initiated a consortium study on the newly found Martian meteorite NWA2737, which contains abundant brown olivine that has been ascribed to high ferric iron content. Interpretation of this meteorite will contribute to our understanding of the alteration of ultramafic rocks on Mars.

We are examining the effects of climate variability on a vegetation-rich biosphere over intermediate time scales, using South American ecosystems as a model. We have identified modern analogs that serve as functional scenarios for past environments inferred from proxy records. We found that (1) pollen stratigraphy offers rich, diverse information to hindcast ecosystems at coarse time scale, (2) tree rings provide the best time resolution, and (3) neural networks are powerful tools to extract climate-related signals from tree rings. Using South America as our ecosphere analog, we are working to hindcast Net Primary Production over the last 750 years. We are currently enlarging our databases to enable hindcasting of the last 2,500 years, which spans the duration of the Subatlantic phase of the Holocene. Our contributions to the investigation, by M. L. Absy in Northeastern Brazil, show changes in the modern ecosystem that can be captured by quantitative models.

We are assessing the potential for life to move beyond its planet of origin and to survive in potentially lethal radiation environments. We conducted fieldwork in the Bolivian Andes at altitudes (~15,000 feet) where the ozone column was substantially reduced and levels of UV radiation were high. We discovered organisms that are previously undescribed and are possibly highly radiation resistant. We developed a high-throughput assay to detect both direct and indirect DNA damage, such as that caused by radiation. To test a potential means whereby microbes might survive interplanetary travel, we are preparing to test the radiation resistance of organisms situated inside meteorites. We obtained samples of breccia that function as analogs of meteorites, and we are determining crack dimensions in collaboration with the Natural History Museum, London. We are developing methods to get microbes in and out of the breccia. We are using these observations to develop a proposal to obtain actual meteorite samples for tests of microbial survival.

The Ames team’s Education and Public Outreach program continues to focus principally on its partnerships with California Academy of Sciences (CAS) and Yellowstone National Park (YNP), but it also pursued other significant activities. The team authored the chapter on thermophiles and astrobiology in the 2005 edition of the recently published Yellowstone Resources and Issues Guide. The first four permanent large “way side” (trail) ceramic signs that interpret thermophilic microorganisms and astrobiology will be installed in YNP this summer. The team submitted extensive recommendations to the “content matrix,” a planning document for the new Old Faithful Visitors Center. The team contributed to astrobiology exhibits at the CAS in San Francisco. A team Co-I was recently appointed to the CAS Exhibit Planning Board. He will serve as an astrobiology specialist in designing a permanent exhibit, “Earth and its Place in the Universe”, for the newly remodeled CAS campus scheduled to open in 2008. This Co-I participated in both the filming of James Cameron’s “Aliens of the Deep” IMAX film and the authorship of the associated educators guide. Two team members are instructors and textbook authors for the current JASON project entitled, “Mysteries of Earth and Mars.” The Ames team and the education office hosted the first “Earth to Sky” interpreters’ training workshop in collaboration with the National Park Service. Ames continues to work with TERC to disseminate its new high school astrobiology course. Several team members gave numerous talks in classrooms and in informal public venues.

The Ames team maintains on ongoing substantial presence on current NASA missions. The P.I. serves as a strategic planning lead on the Science Operations Working Group of the Mars Exploration Rover mission. Another team member was selected as a P.I. of the CheMin XRD spectrometer for the Mars Science Laboratory mission. A third member serves as a co-investigator with the Kepler mission of NASA’s Discovery program. Several team members are involved with the SOFIA mission. Several others are involved with missions that are scheduled or planned for the next several years.