2010 Annual Science Report
NASA Ames Research Center Reporting | SEP 2009 – AUG 2010
The Ames NAI Team addresses the cosmic, planetary, and biological processes that collectively create habitable environments. We trace, spectroscopically, the cosmic evolution of organic molecules from the interstellar medium to protoplanetary disks, planetesimals and finally onto habitable bodies. We characterize the diversity of planetary systems emerging from protoplanetary disks, with a focus on the formation of planets that provide chemical raw materials, energy, and environments necessary to sustain prebiotic chemical evolution and complexity. We develop and evaluate a more quantitative methodology for assessing the habitability of early planetary environments – particularly Mars – via capabilities that will be, or might be, deployed in situ. Finally we identify critical requirements for the emergence of biological complexity in early habitable environments by examining key steps in the origins and early evolution of catalytic functionality and metabolic reaction networks. Our direct involvement in multiple NASA missions provides context, motivation, and collaborative opportunities for our research and our education and public outreach efforts. Please visit www.amesteam.arc.nasa.gov.
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We continued our program to measure the spectra and chemistry of materials under simulated space conditions in the laboratory. We incorporated our unique collection of polycyclic aromatic hydrocarbon (PAH) spectra into a user-friendly database. In August 2010 we launched a web site (Fig. 1) that presents our collection of more than 600 polycyclic aromatic hydrocarbon (PAH) spectra, together with the tools needed to query the data and analyze astronomical spectra.
We published three PAH-related papers to support missions such as Spitzer, SOFIA, Herschel, and JWST (“The Far-Infrared Spectroscopy of Very Large Neutral Polycyclic Aromatic Hydrocarbons,” “Infrared Spectroscopy of Naphthalene Aggregation and Cluster Formation in Argon Matrices,” “The NASA Ames Polycyclic Aromatic Hydrocarbon Infrared Spectroscopic Database: The Computed Spectra”). We published additional work that describes a detailed lab study of the photochemical kinetics of several PAHs in cosmic ice analogs (“Photochemistry of the PAH Pyrene in Water Ice: the Case for Ion-Mediated Ice Astrochemistry,”). The study provides the first solid-state reaction rates needed to model extraterrestrial ice chemistry from the Solar System to the ISM. This novel modeling capability opens a major new field of research.
We published one paper and are working on others that describe the production of prebiotic compounds by UV irradiation of cosmic ices. The paper published in Astrobiology showed that the photolysis of pyrimidine in H2O ices produces a host of new compounds, including the nucleobase uracil (Fig. 2). A manuscript (in preparation) shows that the addition of ammonia to the ice results in the production of the nucleobase cytosine.
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NAI Wisconsin team member Pascale Ehrenfreund, collaborating with Ames Team members Allamandola and Mattioda, received an NAI DDF grant to investigate the modification of organic materials (particularly PAHs) under interstellar conditions via UV-Visible spectroscopy. This DDF project employs post-doctoral researcher Kathryn Bryson, who has set up the UV-Vis spectrometer system and has begun a spectroscopic study of thin films of astrobiologically interesting organic molecules.
Dr. Sandford continues to be involved with the extraction, distribution, and analysis of samples from Comet 81P/Wild 2 returned by the Stardust mission (two related papers in the last year). He also continues to work as a Co-I on the Hayabusa asteroid sample return mission, which returned samples to Earth in June 2010 and is now actively studying these samples. Dr. Mattioda is a member of the Science Team for the O/OREOS (Organisms/ORganics Exposure to Orbital Stresses), NASA’s first Astrobiology Small Payloads mission. He and Dr. Bramall are working on the SEVO (Space Environment Viability of Organics) component for O/OREOS.
The Ames team continued its investigations of the processes leading to the development of habitable planets in protoplanetary disks. Dr. Gorti presented our group’s work on time-dependent evolution of viscous disks subject to photoevaporation by Ultraviolet and X-ray photons from the central star at the Circumstellar Disks meeting at ESO, Garching, Germany. Typical disk lifetimes are ~4 to 5 million years. Disks disperse by first forming gaps at a few AU and then are eroded outwards. Disk lifetimes are roughly independent of stellar mass and other properties for low-mass stars with M<3 solar masses. Higher mass stars have highly mass-dependent disk lifetimes, with more massive disks destroying their disks very rapidly. Gorti and Hollenbach are also modeling the observed gas line emission from disks. Their models of the star TW Hya suggest that the disk harbors a Jovian mass planet and is being destroyed by photoevaporation (Astrophysical Journal, submitted). Gorti presented these results at a recent Herschel meeting on star and planet formation at Goteburg, Sweden. Gorti and Hollenbach will continue to model other interesting circumstellar disks and apply their theoretical models to infer disk masses. They are also developing models that combine dust evolution, viscous evolution and photoevaporation simultaneously in collaboration with Dr. C. P. Dullemond (MPIA, Heidelberg).
Drs. S. Davis and D. Richard continue work on models of large-scale transport in protoplanetary disks. Davis published a paper on the LCROSS impact event. Richard is developing models of optical scattering by dust grains that will be published this year. This work will further our understanding of scattering from small dust particles in both the nebula and in tenuous atmospheres such as the Moon and larger asteroids. S. Davis and D. Richard reported work on the transport properties of chemically induced oxygen isotope distributions in disks at the 2010 Astrobiology Science Conference. Accordingly we can study the migration of these species into the planet-building zones and ultimately into the meteoritic record where these interesting isotopic anomalies are recorded. Davis has written a paper (in review) on the location of water ice in the protoplanetary nebula and its ramifications for the habitability of extrasolar planets.
Dr. Laughlin continues to lead the development of the publicly available Systemic Console software for the analysis of radial velocity and photometric data sets for extrasolar planets. He implemented routines for rapidly integrating the long-term evolution of model planetary systems, as well as routines for solving the transit timing inverse problem. The Console software was used to detect and analyze a number of planetary systems, including 61 Vir b,c, and d, which is a newly discovered planetary system with three Super-Earth category planets orbiting a nearby solar-type star. Laughlin published this work in two peer-reviewed articles.
The Ames Team also seeks to characterize the habitability (potential to support life) of ancient Martian environments, with an emphasis on understanding environments that could have supported more life than others. Efforts during this performance period have focused on (1) development and application of cell-scale bioenergetic models; (2) characterization of mineralogy in samples collected from relict alteration deposits of the Josephine Ophiolite Complex and Spitzbergen, Norway; and (3) parallel characterization of aqueous chemistry and biological diversity in samples collected from several actively serpentinizing systems.
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We developed a cell-scale reaction transport model for determining single cell power generation for a defined metabolism in a medium of specified composition. The model determined diffusion in three dimensions (using a spherical cell), and includes biologically realistic membrane transport properties.
Team members conducted bulk mineralogical analyses on samples collected from the Josephine Ophiolite Complex (northern California and southern Oregon; Fig. 3), and from Spitzbergen, Norway (Fig. 4), as the basis for conducting mineralogy-based assessments of habitability, and to augment a library of reference spectra for instruments that will fly on MSL. We conducted paired analyses of aqueous chemistry and presence or absence of functional genes associated with target metabolisms, in samples collected from a range of actively serpentinizing systems. We utilized chemistry measurements to determine Gibbs energy availability and, in some cases, power availability (via the modeling described above (1)).
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The Ames Team is also identifying critical requirements for the emergence of biological complexity in early habitable environments by examining key steps in the origins and early evolution of functional proteins and metabolic reaction networks. We have been characterizing an artificial enzyme that joins two RNA fragments. This enzyme was previously generated de novo from a large library of proteins based on a zinc finger protein scaffold with randomized loops. Structural investigations by Nuclear Magnetic Resonance (NMR) have generated sufficient data to model an ensemble of its structures (Fig. 5a). The protein has a highly compact core composed of two regions connected by a flexible loop and very flexible ends. NMR data suggest that two zinc-binding sites are located in the compact core. The protein structure is unrelated to the original scaffold and has no homology to other known structures. This indicates that (1) protein evolution through a modest number of mutations can yield both novel functions and novel structures, and (2) structures and functions not found in contemporary organisms are possible. We have generated over 20 mutant proteins (Fig. 5b) to identify the zinc-binding sites and the amino acids involved in catalysis.
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We investigated two models of protobiological protein ion channels, antiamoebin and trichotoxin. These channels facilitate ion transport across cell walls that protocells would have required in order to establish osmotic equilibria, energy transduction and stabilize key macromolecules. Peptides forming the channels consist of only 14-16 residues and contain non-standard amino acids that were common on the early earth. By comparing calculated and measured conductance we determined the channel structures (Fig. 6). Despite their simplicity the channels are quite efficient in increasing rates of ion transport through membranes, a property that is essential for preventing the buildup of osmotic stresses. The specific identity of many amino acids in these channels is not important, as long as their polarity is conserved, a convenient property at the origins of life. Our results support a view that the first ion channels were similar to the channels studied here.
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The entire Ames Team has pursued diverse education and public outreach (EPO) activities that included efforts in high-impact public venues. Team research efforts have contributed source material for the team’s EPO program. We implemented a graduate-level astrobiology course at the University of California at Santa Cruz. We gave numerous lab tours and demonstrations to students and educators. We made presentations to K-12 classrooms, universities, museums, planetariums, national park visitor centers, scientific conferences, and the media.
The Ames Team continued to forge its strong partnership with Lassen Volcanic National Park by reinforcing the connections between microbiology and astrobiology. Team members, high school students, educators and park rangers participated in fieldwork (Fig. 7) and collected data from thermal features for NASA astrobiologists, classroom lectures, and public talks. The students examined hydrothermal features in the park and generated a database of temperature, pH, GPS coordinates, photos, and geochemical analyses that will be hosted on the NASA Ames Team website.
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Lassen staff installed the first of ultimately four or more astrobiology-interpretive-trailside signs. These signs will be located at hydrothermal sites that best illustrate the most compelling aspects of astrobiology research in Lassen. The Ames Team supported the implementation by Lassen Park of a Junior Park Astrobiology program for 5th through 12th graders during the upcoming school year.
The Ames Team has partnered with the Choctaw Nation to provide Native American students and their teachers with access to NASA astronomers, scientists and astrobiology curriculum via five interactive seminars using NASA’s Digital Learning Network. The lectures encompassed topics such as cosmochemistry and astrobiology.
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; he is also Chair of MEPAG (NASA’s Mars Exploration Program Analysis Group). 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 Observer for Infrared Astronomy, Mars Reconnaissance Orbiter, MSL, James Webb Space Telescope, Spitzer Space Telescope, Herschel, O/OREOS, ABE/ASPIRE, LCROSS, LADEE, and Comet Coma Rendezvous Sample Return Mission.