nai

Project Progress

2009 featured the sixth SUIA offering (Summer Undergraduate Internships in Astrobiology), a ten-week residential research program at the Goddard Center for Astrobiology (GCA). http://astrobiology.gsfc.nasa.gov/education.html Competition was very keen, with an oversubscription ratio of 3.0. Students applied from over 28 colleges and universities in the United States, and 6 Interns from 6 institutions were selected. Each Intern carried out a defined research project working directly with a GCA scientist at Goddard Space Flight Center or the University of Maryland. As a group, the Interns met with a different GCA scientist each week, learning about his/her respective area of research, visiting diverse laboratories and gaining a broader view of astrobiology as a whole. During a Field Trip to the National Radio Astronomy Observatory in Greenbank, West Virginia, Interns toured the Telescope Operations Facility that monitors and controls the Robert C. Byrd Green Bank Telescope (GBT). The GBT is the most technically advanced single-dish radio telescope in the world. Its 110-meter by 100-meter dish boasts more than two acres of area for collecting faint radio waves from the Universe. Weighing 17 million pounds, the GBT is also one of the world’s largest moving structures on land. The Interns also learned how to operate the 40ft Telescope, acquired a radio map of the galactic center that night, and presented their results the following day. At summer’s end, each Intern reported his/her research in a power point presentation projected nation-wide to member Teams in NASA’s Astrobiology Institute, as part of the NAI Forum for Astrobiology Research (FAR) Series.

http://astrobiology.nasa.gov/nai/seminars/detail/157

Brief Summaries of Research are given below:

Nadezhda Radeva (Connecticut College) – “Mapping the D/H ratio in water on Mars: Searching for active vents”
Ms. Wright studied the atmosphere of Mars as revealed through high-resolution infrared spectra acquired with the NIRSPEC cross-dispersed echelle spectrometer at the W. M. Keck Observatory atop Mauna Kea, Hawaii. During her Internship, Nadia learned to analyze infrared spectra using our latest processing techniques, in which the raw spectral-spatial frames are cropped, straightened, and registered using custom IDL algorithms. These routines also include correction (with milli-pixel precision) of spatial and spectral distortions introduced by anamorphic optics in the spectrometer, removal of internal scattered-light, correction of variable resolving power, removal of spectral fringing (using Lomb periodogram analysis), correction of residual dark current, and correction of residual telluric radiance. Beginning with raw spectra, Nadia performed pipeline processing to the entire 1-5 µm spectral region. Many molecules of possible biological and geothermal origin have strong signatures in this spectral region.

GCA Collaborator Dr. Geronimo Villanueva (NASA-GSFC) mentored Ms. Radeva

Keara Wright (University of Missouri, St. Louis) – “H₂O in Comet C/2001 A2 (LINEAR) and C/2007 W1 (Boattini)”
Ms. Wright studied emission of cometary water – the most abundant volatile constituent released from the nuclei of active comets. Keara analyzed H₂O emission spectra of comets C/2001 A2 (LINEAR) and C/2007 W1 (Boattini) and extracted rotational and spin temperatures for water in these comets. The rotational temperature reflects conditions in the collisionally dominated inner coma (an expanding atmosphere surrounding the cometary nucleus), but the spin temperature has long been considered a possible (though not certain) measure of the chemical formation temperature of H₂O in pre-cometary ice. Thus, the two temperatures should differ. Keara Wright found that the rotational temperature decreased with increasing distance from the nucleus in the coma of comet Boattini, and she showed that the spin temperature was lower than the rotational temperature at all nucleocentric distances. Her results demonstrate for the first time that the spin temperature in water differed substantially from the rotational temperature and remained constant in the inner coma, in agreement with the hypothesis that the spin temperature is cosmogonic invariant.

GCA Collaborator Dr. Boncho P. Bonev (NASA-GSFC) mentored Ms. Wright.

Karen Whelley (Pennsylvania State University) – “Derivatization of Dicarboxylic and Hydroxy Acids with IPA/TFAA”
Ms. Whelley pursued three projects in the Astrobiology Analytical Laboratory. Ms. Whelley investigated novel extraction and gas chromatography derivatization techniques for small hydroxy acids. The purpose is to add the minimum number of carbons/molecule for increased precision in our isotopic ratio mass spectrometric analysis of carbonaceous meteorites. Unfortunately the propyl ester derivatives of these compounds were too volatile and they were largely lost in work-up.

Ms. Whelley also worked on observing the reaction of fluorescent purines with products of Miller-Urey-type spark discharge experiments. This project was much more successful, and this very complex reaction resulted in a very small number of products. The identity of these will be confirmed next summer when Ms. Whelley will return to GSFC in partial fulfillment of her Ph.D. Ms. Whelley assisted in the extraction and characterization of nucleobases from several carbonaceous meteorites. This work was highly successful – a publication is being prepared for submission to Geochimica et Cosmochimica Acta.

GCA Co-Investigator Dr. Jason Dworkin (NASA-GSFC) mentored Ms. Whelley.

William Herlands (Princeton University) – “Towards an Empirical Model for Methanol Spectra in Comets”
Mr. Herlands’ project was to build an empirical fluorescence model for methyl alcohol (methanol, CH3OH) based on high-resolution infrared spectra of comets. CH3OH is known to be present in and to have varying abundances among comets. Laboratory experiments demonstrate a viable means of its production to be low temperature (T < 25 K) H-atom addition reactions to CO condensed on the surfaces of interstellar grains prior to their incorporation into comets. These reactions proceed through formaldehyde (H₂CO), which is fundamental to the production of sugars and so is of high significance to Astrobiology. Co-I Dr. Michael A. DiSanti (NASA-GSFC) mentored Mr. Herlands.

For most parent molecules that we measure in comets, we extract parameters such as rotational temperature and production rates by applying rigorous quantum mechanical fluorescence models to their infrared spectra. However, highly accurate quantum mechanical band models do not exist for vibrational bands of methanol, so our existing model for CH3OH does not adequately reproduce the line intensities we observe in cometary spectra. The high-resolution near-IR spectrometer (NIRSPEC) at the Keck 10-meter telescope has broad spectral coverage, permitting simultaneous measurement of methanol lines spanning a broad range of rotational energies. A rotational temperature (T_rot) for water can be determined directly from similar measurements and highly accurate models. Comparing empirical methanol line intensities among comets having different T_rot values is expected to provide information on the excitation energies of encompassed CH₃OH lines. Mr. Herlands measured methanol lines in seven comets with T_rot ranging from ~ 50 to 100 K, and obtained temperature-dependent fluorescence efficiencies (g-factors) for several CH₃OH lines. This work is of fundamental importance for obtaining accurate CH3OH abundances in comets using spectra obtained with other instruments having less spectral coverage compared with NIRSPEC.

GCA Co-Investigator Michael A. DiSanti (NASA-GSFC) mentored Mr. Herlands.

Renuka Ramanathan (MIT) – “Laser Desorption ToF-MS for In Situ Analysis of Organics”
Ms. Ramanathan worked on improving approaches to the analysis of chemical composition using a new configuration of a prototype miniature mass spectrometer. The “Tower” time-of-flight mass spectrometer (ToF-MS) is under development for potential landed missions to bodies such as Mars, Titan, or asteroids. By pulsing a solid sample with a focused laser in vacuum, ions are formed whose mass-to-charge (m/z) ratios can be analyzed – helping to determine the composition of the sample more precisely. The Tower ToF prototype has upgraded optical and sample mounting configurations with focusing and positioning elements on micrometer-aligned stages. With greater control over the laser focus on the sample surface, the ion formation conditions can be made more reproducible from analysis to analysis, and the effects of controllable parameters such as laser intensity, analyzer voltages, or sample preparation methods can be quantified.

Using these upgrades, Renuka helped characterize the effects of sample preparation approaches on factors such as analyte mass resolution, signal-to-noise ratios, and fragmentation patterns. Renuka examined carboxylic acid (CBA) standards, benzene di-, tri-, and hexa-CBAs mixed with organic-free reagent sand (high-Fe silica) as a mineral matrix proxy. There is significant interest in the prevalence of extraterrestrial CBAs: they are a core building block of amino and fatty acids in terrestrial biology, they are found in carbonaceous meteorites, and they may be found in abundance on Mars as metastable degradation products of more complex aromatic organics (Benner et al., 2000). CBAs and silica powders were prepared both as “dry” physical mixtures and several types of “wet” deposition from solvents such as dimethylformamide (DMF). Spectra from the dry mixture had the highest mass resolution and accuracy, with distinct elemental peaks from the silica matrix as well as the expected distribution of molecular ion (M) and associated peaks (MH, MNa, M-OH, M-COOH). Solvent-deposited samples produced high signal levels (high overall sensitivity), however the peaks were significantly broadened leading to lower mass resolution and accuracy. Through the characterization of multiple samples and approaches, Renuka proposed several hypotheses for this behavior, such as the redistribution of analyte over the sample. She suggested appropriate follow-up improvements and approaches that are now under investigation.

GCA Co-Investigator Dr. William Brinckerhoff (NASA-GSFC) mentored Ms. Ramanathan.

Joseph Angelo Jr. (Drexel University) – “Homochirality & Prebiotic Chemistry: Theoretical Models of Asymmetric Autocatalysis”
Mr. Angelo modeled asymmetric amplification of enantiomeric excesses in prebiotic chemistry. Many organic molecules can exist in two mirror-symmetric forms; these enantiomers are chiral and so are designated as either left-handed (L) or right-handed (D). Remarkably, all key biological molecules exhibit homochirality – they exist in only one or other chiral state. For example, all the naturally occurring amino acids which form proteins are L, whereas all the sugars in DNA are D. In biochemistry this property is essential for many basic biological processes including molecular recognition and replication. Identifying the mechanism responsible for homochirality in prebiotic chemistry is recognized as a central issue in the problem of the origin of Life.

Most naturally occurring chemical reactions involving chiral molecules produce racemic mixtures: equal amounts of the L and D forms. The homochirality 'problem’ involves identifying physical and/or chemical processes that can produce a slight enantiomeric excess ('ee’_) that then can be amplified to a homochiral state. The fact that significant 'ee’ has been detected in meteoritic amino acids strongly suggests that homochirality may have been a feature of prebiotic chemistry on asteroids or comets, prior to delivery to the early Earth. Many mechanisms, involving both terrestrial and extraterrestrial environments, have been proposed (e.g., polarized UV radiation, crystallization, weak neutral currents, and symmetry-breaking in chemical autocatalysis) but the problem remains unresolved. As early as 1953 Frank proposed a theoretical mechanism for asymmetric amplification based on nonlinear autocatalysis with selective enantiomeric suppression. This work stimulated a great deal of interest but, despite enormous effort, no viable experimental reaction system was ever found with the desired properties. The situation changed dramatically in 1995 when Soai and coworkers discovered an autocatalytic process that could amplify extremely small 'ee’ values to almost complete homochirality. Although the so-called Soai reaction itself probably played no role in prebiotic chemistry, it remains unique in all of organic chemistry for its amplification properties. This has led to an enormous amount of effort to understand the kinetics of this reaction, and to seek new reactions with the property of asymmetric amplification that are more relevant to possible origin of Life scenarios.

This project involved a theoretical study of the kinetics of the Soai reaction and related processes. Mr. Angelo explored relevant chemical kinetic models from the perspective of nonlinear dynamics (chaos, limit cycles etc.), quantifying the stability properties of the nonlinear kinetic system through bifurcation analysis and the calculation of Lyapunov spectra. The models studied were simple realizations of the Frank mechanism (Islas et al. 2005, PNAS, 102, 13743) and those proposed for the kinetics underlying the Soai reaction (Buhse 2005, J. Mex. Chem. Soc., 49, 328). Mr. Angelo employed computational techniques including solution of nonlinear algebraic equations and stiff ordinary differential equations. Even given the limitations imposed by the timeframe of a summer Internship, the insight gained from this limited study is proving important for obtaining general principles that will be useful for proposing new asymmetric autocatalysis processes, especially for reactions that could have produced enantiomeric excesses in meteoritic organic chemistry.

GCA Co-Investigator Dr. Steven Charnley (NASA-GSFC) mentored Mr. Angelo.