FAR Seminars Seminarshttps://nai.nasa.gov/seminars/archived-seminars/far-seminars/FAR Seminars Seminarsen-usSat, 06 Jun 2020 05:26:14 +0000A Record of the Earliest (4.5-3.8 Ga) Surface Conditions on Earth?https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/9/12/a-record-of-the-earliest-45-38-ga-surface-conditions-on-earth/<p class="body">In order to understand the nature of the earliest surface environments on Earth, geological durable materials that retain chemical information bearing on surface conditions are required. In the apparent absence of a rock record from before ca. 4 billion years ago, the only direct means to investigate the Hadean Earth is through detrital zircons, which are resistant to chemical alteration and whose ages are known by <em>in situ </em> ion microprobe U-Th-Pb radiometric dating. </p> <p class="body">Although zircons form predominately in melts of broadly granitoid compositions, oxygen isotopes can be used to evaluate whether the source magma is enriched in heavy oxygen, a sensitive proxy for contamination by anatectic sediments. Zircons derived exclusively from partial melting of relatively unevolved igneous protoliths would have oxygen isotope ratios similar to that of bulk Earth ( <sup>18</sup>O/ <sup>16</sup>O referenced VSMOW; expressed as &#948; <sup>18</sup>O = +5.3 &plusmn; 0.3‰). Some core regions of 4.37-3.8 Ga zircons from quartz pebble conglomerate in the Jack Hills of Western Australia are significantly enriched in <sup>18</sup>O, with values as high as +10.0 ‰. Empirically-derived whole-rock (WR) oxygen isotope fractionation values indicate that the precursor magma of a +10‰ zircon would have had &#948; <sup>18</sup>O WR = +12.0 ‰. This result has been taken as strong evidence for crust interacting with large volumes of (stable) surface water subsequent to zircon crystallization <em>ca. </em> 4.3 Ga. Although water was present, could the Hadean Earth have been habitable? </p> <p class="body">Post main-accretion impact fluxes of comets and asteroids would potentially have had direct influence on, and deleterious consequences for, an emerging biosphere. Lunar meteorite melts and melt-sheet ages for the Moon are contemporaneous with the canonical late heavy bombardment (LHB) epoch up to 3.92-4.0 Ga. Our ultra-high spatial resolution (sub-&micro;m) U-Th-Pb ion microprobe depth profile studies of four ~4.1 Ga zircons record common (3.97-3.94 Ga) metamorphic zircon overgrowth ages with Pb loss; these metamorphic overgrowths are in excellent agreement within error for models of the timing of peak mass flux of the inner solar system linked with the LHB. Whether these rim overgrowths are of impact origin or due to more mundane metamorphic processes in the crust awaits further investigation. </p>https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/9/12/a-record-of-the-earliest-45-38-ga-surface-conditions-on-earth/Simulating Groundwater Radiolysis With Oxidation of Pyrite by Hydrogen Peroxide Solutionhttps://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/8/8/simulating-groundwater-radiolysis-with-oxidation-of-pyrite-by-hydrogen-peroxide-solution/Radiolytic dissociation of water produces oxidizing (e.g., H<sub>2</sub>O<sub>2</sub>, OH·, and O<sub>2</sub>) and reducing (e.g., H atoms and H<sub>2</sub>) species. In natural environments, radiolytically generated oxidants can react with sulfide minerals (e.g., pyrite) and can provide local sources of partially to fully oxidized sulfur species suitable for microbial metabolism. <br><br> In this study, we investigate the reaction of pyrite with millimolar solutions of H<sub>2</sub>O<sub>2</sub> at temperatures from 4 to 150ºC. Results show that radiolytically produced oxidants could efficiently oxidize pyrite in an otherwise oxygen-limited environment. The rate of pyrite oxidation increases with increasing peroxide concentration, pyrite surface area, and temperature. <br><br> In natural groundwater environments where radiolysis occurs, coupled abiotic and biotic reactions could complicate the products of radiation-induced chemical reactions. Radiolytic pyrite oxidation can buffer oxygen production, maintain anaerobic conditions, and supply partially to fully oxidized sulfur species for microbial reduction or disproportionation.https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/8/8/simulating-groundwater-radiolysis-with-oxidation-of-pyrite-by-hydrogen-peroxide-solution/Exploring Planet-Forming and Debris Diskshttps://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/6/20/exploring-planet-forming-and-debris-disks/Understanding the formation and evolution of life in the galaxy requires an understanding of the birth and evolution of planetary systems. The planets of our solar system formed in a circumstellar disk, and such disks have been observed around both young and evolved stars. We will present an overview of several observational projects to explore the properties of such circumstellar disks, including infrared photometry, disk imaging and spectroscopy. We report on studies of disks around objects with masses ranging from substellar to a few solar masses, investigating their structure and mineralogical composition.https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/6/20/exploring-planet-forming-and-debris-disks/Quantifying Water Production in Comets - The "Meter Stick" for Their Chemical Taxonomyhttps://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/5/16/quantifying-water-production-in-comets-the-meter-stick-for-their-chemical-taxonomy/Boncho P. Bonev<br> Ritter Astrophysical Research Center, Dept. of Physics and Astronomy<br> The University of Toledo and Solar System Exploration Division, NASA's GSFC<br> bbonev@kuiper.gsfc.nasa.gov <br><br> Michael J. Mumma - thesis advisor <br><br> An intense cometary bombardment during the early stages of Earth history might have played a major role in delivering the water and organics that subsequently formed the biosphere. Consequently, the chemical composition of the cometary nucleus (and its diversity) is a key issue for astrobiology. While comets are often grouped according to their orbital properties, it is increasingly clear that such groups likely contain comets formed in diverse regions of the proto-planetary disk. In recent years the emergence of accurate abundance measurements has begun to permit a taxonomic classification based on chemistry. This requires an accurate "meter-stick" (the H2O production rate) against which the abundances of minor cometary constituents are compared, including biologically important molecules. <br><br> Two methods for deriving cometary water production rates from ground-based high-resolution infrared spectra have now been developed. The H2O population can be directly sampled through "hot-band" fluorescent emission [c.f. Dello Russo et al. 2000, Icarus]. More recently, vibrational prompt emission from OH has also been used as a proxy for water production [Bonev et al. 2004, ApJ]. I will review these two methods using specific examples from my thesis work. I will present new results on the Oort Cloud comet C/2000 WM1 (LINEAR). In particular, I will show how we retrieve the rotational temperature and the spin temperature of H2O. While the former parameter reflects the conditions in the collision-dominated inner coma of the comet, the spin temperature might be a measure of the formation temperature of water in comets. I will also show the first measurements of OH emission efficiencies for quantum states spanning a wide range of rotational quantum numbers.https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/5/16/quantifying-water-production-in-comets-the-meter-stick-for-their-chemical-taxonomy/Remote Sensing of Life and Habitable Worlds: Habstars, Earthshine, and the Challenge of TPFhttps://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/3/14/remote-sensing-of-life-and-habitable-worlds-habstars-earthshine-and-the-challenge-of-tpf/NASA's coronagraphic version of the Terrestrial Planet Finder (TPF-C) is scheduled for launch in ~2014 to directly image terrestrial planets orbiting within the habitable zones of nearby stars. With this stated objective, there is clearly a built-in consideration of life and the hope of finding habitable (or inhabited) worlds. But which stars should we, or can we, observe? With the capability to search only 35 to 165 stars, and a price tag of more than $1 billion, one of the most controversial problems that scientists and engineers are now facing is that of target selection. In the first part of this talk we will discuss the challenges, both scientific and instrumental, in picking target stars. On the science side of things, we will review the concept of "habstars," stars that could set up favorable conditions for life as we know it on Earth. On the engineering side of things, we will also look at TPF's likely limitations for planet detection. But how many habstars actually meet the engineering criteria? Can we create a list of stars that is both scientifically interesting and observationally feasible?https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/3/14/remote-sensing-of-life-and-habitable-worlds-habstars-earthshine-and-the-challenge-of-tpf/Life of a Permafrost Bacterium: Psychrobacter 273-4 Reveals Ways to Adapthttps://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/2/14/life-of-a-permafrost-bacterium-psychrobacter-273-4-reveals-ways-to-adapt/Siberian permafrost with its continual low temperatures (-10°C) and associated decreased water activity is seen as a model environment for assessing potential survival mechanisms of life on astral bodies. Ice formation increases solute concentration by decreasing the amount of free water available in the remaining unfrozen water films (aw=0.85-0.9), making this condition even more stressful to microbial cells. The majority of permafrost isolates grow under increased osmotica, in addition to temperatures as low as ­10°C. <p class="body"> To gain knowledge of the features for adaptation to low temperature and water activity, the genome of a Siberian permafrost isolate was sequenced. Psychrobacter 273-4, a gamma-Proteobacterium grows at temperatures as low as ­10°C and displays marked physiological changes under low temperature vs. mesophilic growth and in the presence of increased osmotica (salt). Known cold and salt responsive genes are present in the genome. Differential gene expression analyses, using microarrays specific for the predicted genes of Psychrobacter 273-4, at 4°C and 22°C reveal 2-fold or greater up-regulation at 4°C for a number of genes necessary for energy metabolism and maintenance of membrane fluidity. Several transport genes and potential amino acid metabolism operons, implicated in compatible solute production in other bacteria are differentially expressed. The expression patterns of these transport genes support physiological evidence that different carbon sources are utilized at the two temperatures. The majority of genes down-regulated (2-fold or greater) when grown in the presence of 5% NaCl are involved in cation transport, indicating a systemic response to limit NaCl transport into the cell. Up-regulation of a gene predicted to be involved in cell shape correlates with increased cell size in the presence of 5% NaCl. In addition, general stress response chaperones are upregulated under both increased salinity and decreased temperatures. Several genes with unknown functions are upregulated under both stresses, indicating their possible importance in stress survival. The gene expression profiles and physiological responses of Psychrobacter 273-4 to low temperature and increased osmotica indicate that they have adapted to the low water activity and subzero temperatures of the permafrost environment.</p>https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2005/2/14/life-of-a-permafrost-bacterium-psychrobacter-273-4-reveals-ways-to-adapt/Biogeochemical Responses to the Changing Paleoproterozoic Atmospherehttps://nai.nasa.gov/seminars/archived-seminars/far-seminars/2004/9/13/biogeochemical-responses-to-the-changing-paleoproterozoic-atmosphere/Planetary scale changes in the redox state of the Paleoproterozoic atmosphere and hydrosphere have profoundly affected the evolution of life on Earth. The accumulation of oxygen in the atmosphere is the result of oxygenic photosynthesis, which is thought to have evolved prior to 2.7 Ga. The Paleoproterozoic carbon cycle has experienced dramatic variations with world-wide carbonate occurrences that recorded excursions of isotopically heavy carbon, consistent with the oxygenation of the atmosphere. The nitrogen cycle also appears to have evolved from the anoxic Archean atmosphere, where biological nitrogen fixation was dominant, to the oxygenated Proterozoic and Phanerozoic terrestrial surface where denitrification became dominant. The oxygenation of the atmosphere can be traced with multiple sulfur isotopes, which are known to fractionate independently from their masses during the ultraviolet photolysis of reduced or oxidized sulfur gases. Mass independently fractionated (MIF) sulfur isotopes often occur in Archean sedimentary sulfides and sulfates, but very rarely in rocks younger than 2.0 Ga. This observation is consistent with the transition from an anoxic Archean atmosphere devoid of an ozone layer to an oxygenated atmosphere more similar to the modern atmosphere. New multiple sulfur isotopic analyses (32S, 33S, and 34S) of sulfides by multicollector secondary ion mass spectrometry confirm that the MIF signal is lost during the Paleoproterozoic. Variations in the sulfur isotopic composition of Paleoproterozoic sulfides (d34S) may indicate periods of higher or lower seawater sulfate concentration and may help to understand the biogeochemical changes induced by the accumulation of atmospheric oxygen.https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2004/9/13/biogeochemical-responses-to-the-changing-paleoproterozoic-atmosphere/Amanda Cook, Anita Ganesan, Nida Rauf and Marina Yoderhttps://nai.nasa.gov/seminars/archived-seminars/far-seminars/2004/8/9/amanda-cook-anita-ganesan-nida-rauf-and-marina-yoder/Students from the GSFC 2004 Summer Undergraduate Internship in Astrobiology (SUIA): <p class="body"> Amanda Cook (Connecticut College): "Interstellar Synthesis of Glycoaldehyde: A Laboratory Study" <p class="body"> Anita Ganesan (Cornell University): "Smokes & Mirrors: A Spectroscopic Analysis of Insterstellar Dust Grains" <p class="body"> Nida Rauf (Salem College): "Mapping HDO on Mars" <p class="body"> Marina Yoder (Smith College): "Defining the Edge: Planets and the Spectrum of Earthshine"https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2004/8/9/amanda-cook-anita-ganesan-nida-rauf-and-marina-yoder/Establishing a Baseline for Antarctic Meteorite Research Through the Antarctic Meteorite Contamination Study (AMCS)https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2004/7/12/establishing-a-baseline-for-antarctic-meteorite-research-through-the-antarctic-meteorite-contamination-study-amcs/Work performed to date on Antarctic meteorites by the scientific community has shown the presence of contamination to an uncertain degree. This contamination allows ambiguity to creep into conclusions drawn from Antarctic meteorite research. In order to establish a baseline understanding of the state of meteorites collected in Antarctica, a multidisciplinary effort is under development to measure those types of contamination that should most strongly affect the commonly-measured aspects of meteorites. Microbial abundance per unit volume, metabolic activity, and genetic expression will be measured to establish the presence and activity of bacteria, yeasts, fungi, mold, and other microbes. ToF-SIMS and pyrolysis-GC-MS will be employed to measure and map the presence of carbon compounds such as amino acids, petroleum products, plastics and plasticizers. A suite of stable isotope analyses will establish trends in carbon, nitrogen, and oxygen isotopes and 14C dating/terrestrial carbon abundance will be performed. In order to separate the effects of terrestrial (ice-bound) contamination, contamination during collection/curation, and accrued contamination during storage, ordinary chondrites from long-term storage, before collection and after curation will be sampled and analyzed by these methods. This project is currently under preparation as a proposal and will be described for discussion and critique by the audience. This project may potentially have a broad impact on the meteoritic community and audience commentary is encouraged.https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2004/7/12/establishing-a-baseline-for-antarctic-meteorite-research-through-the-antarctic-meteorite-contamination-study-amcs/A New Model for the Origin of Proto-Informational Oligomeric Material on the Early Earth, and Elsewherehttps://nai.nasa.gov/seminars/archived-seminars/far-seminars/2004/7/12/a-new-model-for-the-origin-of-proto-informational-oligomeric-material-on-the-early-earth-and-elsewhere/Many of the suggested definitions for the phenomenon of life stress the fundamental importance of oligomeric species demonstrating storable, replicable, and evolvable informational capacity. The chemical problem of the origin-of-life might therefore reduce to a prebiotically plausible mechanism for the formation of a first generation of proto-informational oligomeric material on the early Earth. This talk will present an outline of a new chemical model which is currently being developed, and which would seem to be on the way to providing an intuitively satisfying solution to the problem of the origin of the first proto-informational oligomers at the origin of life.https://nai.nasa.gov/seminars/archived-seminars/far-seminars/2004/7/12/a-new-model-for-the-origin-of-proto-informational-oligomeric-material-on-the-early-earth-and-elsewhere/