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At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Isotopic Signature of the Ancient Biosphere

The age distribution of 261 field localities, sampled for their well-preserved Archean and Proterozoic sedimentary rocks, revealed a 500-700 Ma episodicity. Assuming that the numbers of sites are a proxy for mass of sediments, the record of well-preserved sediments is more abundant in the intervals 3.5-3.3, 2.8-2.5, 2.1-1.8, 1.5-1.3, and 1.0-0.54 Ga than in the intervening intervals. It is proposed that the crustal inventory of photosynthetic organic carbon was modulated by the volume of sedimentation in sites favorable for the burial and long-term preservation of organic carbon. Tectonic processes controlled this sediment volume. Episodic increases in the organic inventory led to stepwise increases in oxidized reservoirs (e.g., O2, SO4(2-), Fe(3+). The interval 2.9-2.5 Ga recorded a large rise in seawater Sr-87/Sr-86, the oldest-known extensive banded iron formations, and the first evidence (C-13-depleted kerogens) of O2 use by methylotrophic bacteria. The interval 2.2-1.8 Ga has both carbon isotopic evidence for a stepwise increase in the organic reservoir and also paleosol evidence for an O2 increase. The interval 1.1-0.6 Ga shows isotopic evidence for another organic carbon increase. The interval 1.5-1.3 Ga revealed no such increases as yet, perhaps because incomplete rifting of the mid-Proterozoic supercontinent was associated with extensive sedimentation in oxidized continental basins, producing redbeds, coarse clastics, etc. Such sedimentation did not promote the burial of reduced carbon.

DesMarais, D. J.↗
NASA NTRS2002

Using Support Vector Machines to Automatically Extract Open Water Signatures from POLDER Multi-Angle Data Over Boreal Regions

This study used Support Vector Machines to classify multiangle POLDER data. Boreal wetland ecosystems cover an estimated 90 x 10(exp 6) ha, about 36% of global wetlands, and are a major source of trace gases emissions to the atmosphere. Four to 20 percent of the global emission of methane to the atmosphere comes from wetlands north of 4 degrees N latitude. Large uncertainties in emissions exist because of large spatial and temporal variation in the production and consumption of methane. Accurate knowledge of the areal extent of open water and inundated vegetation is critical to estimating magnitudes of trace gas emissions. Improvements in land cover mapping have been sought using physical-modeling approaches, neural networks, and active microwave, examples that demonstrate the difficulties of separating open water, inundated vegetation and dry upland vegetation. Here we examine the feasibility of using a support vector machine to classify POLDER data representing open water, inundated vegetation and dry upland vegetation.

Pierce, J.↗
NASA NTRS2002

Observational Signatures of Black Holes: Spectral and Temporal Features of XTE J1550-564

The theoretical predictions of the converging inflow, or Bulk-Motion Comptonization model are discussed and some predictions are compared to X- and gamma-ray observations of the high-soft state of Galactic black hole candidate XTE J1550+564. The approx. 10(exp 2)-Hz QPO phenomenon tends to be detected in the high-state at times when the bolometric luminosity surges and the hard-powerlaw spectral component is dominant. Furthermore, the power in these features increases with energy. We offer interpretation of this phenomenon, as oscillations of the innermost part of the accretion disk, which in turn supplies the seed photons for the converging inflow where the hard power-law is formed through Bulk Motion Comptonization (BMC). We further argue that the noted lack of coherence between intensity variations of the high-soft-state low and high energy bands is a natural consequence of our model, and that a natural explanation for the observed hard and soft lag phenomenon is offered. In addition, we address some criticisms of the BMC model supporting our claims with observational results.

Titarchuk, Lev↗
NASA NTRS2002

Nature of the Organic Signature in Dust from the Interstellar Medium: Laboratory Analog Studies

We measured the infrared (IR) nu(sub CH) absorption bands around 3.4 microns (2800 - 3000 cm(sup -1) in large laboratory-grown magnesium oxide (MgO) and natural olivine single crystals that crystallized from CO/CO2/H2O saturated melts. These bands are very similar to those from many astronomical sources, such as from dust in the diffuse interstellar medium (ISM), from the outflow of evolved stars, etc., and they are characteristic of aliphatic -CH2- and -CH3 entities. In our laboratory single crystals the VCH bands arise from C-H entities that were introduced by a solid solution process, and that are imbedded in the mineral matrix in form of polyatomic C(sub n) entities with C atoms bonded to O and to H. Heating breaks the C-H bonds, causing hydrogen to disperse in the mineral matrix. C-H bonds are re-established rapidly during annealing. We propose that dust grains probably contain the same type of internal C(sub n)-H entities in solid matrix rather than an external organic layer covering the grain surfaces. Thermodynamical arguments show that the concentration of organics in solid solution in small grains can be comparable to that found in astronomical environments.

Freund, M. M.↗
NASA NTRS2003

Jupiter Icy Moons Tidal Signatures and Ocean Mapping from Orbit

Following the Galileo spacecraft encounters with Europa, Ganymede, and Callisto, evidence emerged suggesting that these Galilean moons of Jupiter may have liquid oceans underneath their icy shells. Detection of the oceans on one or all three moons will have profound implications on probability of life beyond the Earth. The icy satellites also have tidal environments that are among the strongest in the solar system. The leading time-varying tidal forcing term on the surface of Europa is at least 9 times larger than those on the inner planets. Tidal forcing on the surfaces of Ganymede and Callisto are about 10% and 7%, respectively, of that on Europa. Since a planetary body with internal fluid deforms more than an otherwise solid body, tidal measurements offer exciting opportunities to detect the oceans.

Wu, X.↗
NASA NTRS2003

Beagle 2: Seeking the Signatures of Life on Mars

Beagle 2 is a 60 kg probe (with a 30 kg lander) developed in the United Kingdom for inclusion on the European Space Agency s 2003 Mars Express. Beagle 2 will deliver to the Martian surface a payload which consists of a high percentage of science instruments to landed spacecraft mass. Beagle 2 will be launched in June 2003 with Mars Express on a Soyuz-Fregat rocket from the Baikonur Cosmodrome in Kazakhstan. Beagle 2 will land on Mars in December 2003 in Isidis Planitia (approx. 11.5 deg.N and 275 deg.W), a large sedimentary basin that overlies the boundary between ancient highlands and northern plains. Isidis Planitia, the third largest basin on Mars, which is possibly filled with sediment deposited at the bottom of long-standing lakes or seas, offers an ideal environment for preserving traces of life. Beagle 2 is completed and undergoing integration with the Mars Express orbiter prior to launch.

Everette K Gibson Jr.↗
NASA NTRS2002

Relative Amino Acid Concentrations as a Signature for Parent Body Processes of Carbonaceous Chondrites

Most meteorites are thought to have originated from objects in the asteroid belt. Carbonaceous chondrites, which contain significant amounts of organic carbon including complex organic compounds, have also been suggested to be derived from comets. The current model for the synthesis of organic compounds found in carbonaceous chondrites includes the survival of interstellar organic compounds and the processing of some of these compounds on the meteoritic parent body. The amino acid composition of five CM carbonaceous chondrites, two CIs, one CR, and one CV3 have been measured using hot water extraction-vapor hydrolysis, OPA/NAC derivatization and high-performance liquid chromatography (HPLC). Total amino acid abundances in the bulk meteorites as well as the amino acid concentrations relative to glycine = 1.0 for beta-alanine, alpha-aminoisobutyric acid and D-alanine were determined. Additional data for three Antarctic CM meteorites were obtained from the literature. All CM meteorites analyzed in this study show a complex distribution of amino acids and a high variability in total concentration ranging from approx. 15,300 to approx. 5800 parts per billion (ppb), while the CIs show a total amino acid abundance of approx. 4300 ppb. The relatively (compared to glycine) high AIB content found in all the CMs is a strong indicator that Strecker-cyanohydrin synthesis is the dominant pathway for the formation of amino acids found in these meteorites. The data from the Antarctic CM carbonaceous chondrites are inconsistent with the results from the other CMs, perhaps due to influences from the Antarctic ice that were effective during their residence time. In contrast to CMs, the data from the CI carbonaceous chondrites indicate that the Strecker synthesis was not active on their parent bodies.

Botta, Oliver↗
NASA NTRS2003

Modern Microbial Fossilization Processes as Signatures for Interpreting Ancient Terrestrial and Extraterrestrial Microbial Forms

Terrestrial biotas from microbially dominated hypersaline environments will help us understand microbial fossilization processes. Hypersaline tolerant biota from Storr's Lake, San Salvador Island (Bahamas), Mono Lake (California), and the Dead Sea (Israel) represent marine and nonmarine sites for comparative studies of potential analogs for interpreting some Mars meteorites and Mars sample return rocks [1,2,3,4,5,6]. The purpose of this study is to compare microbial fossilization processes, the dominant associated minerals, and potential diagenic implications.

Morris, Penny A.↗
NASA NTRS2004

Deconvolving Terrestrial Alteration Mineral Spectral Signatures from Meteorite Reflectance Measurements

When a meteorite enters into the earth's atmosphere, it is immediately subjected to various chemical reactions between its minerals and the elements in our thick atmosphere. These reactions alter the mineralogy of the meteorites. Some examples of the altered minerals in some meteorites are summarized. If meteorites can be linked to their corresponding parent body asteroid in space, we can improve our understanding of the solar system. Spectroscopy has been used in determining the links between asteroids and meteorites. However, meteorite weathering in the Earth s atmosphere also has an effect on meteorite spectra, and altered spectra can easily confuse asteroid connections. The goal of this project is to study the mineral and spectral changes due to Earth's environment and to design a computer simulation to correct meteorite spectra for the effects of terrestrial weathering.

Shah, Sweta↗
NASA NTRS2004

Chicxulub Impact Melts: Geochemical Signatures of Target Lithology Mixing and Post-Impact Hydrothermal Fluid Processes

Impact melts within complex impact craters are generally homogeneous, unless they differentiated, contain immiscible melt components, or were hydrothermally altered while cooling. The details of these processes, however, and their chemical consequences, are poorly understood. The best opportunity to unravel them may lie with the Chicxulub impact structure, because it is the world s most pristine (albeit buried) large impact crater. The Chicxulub Scientific Drilling Project recovered approx. 100 meters of impactites in a continuous core from the Yaxcopoil-1 (YAX-1) borehole. This dramatically increased the amount of melt available for analyses, which was previously limited to two small samples N17 and N19) recovered from the Yucatan-6 (Y-6) borehole and one sample (N10) recovered from the Chicxulub-1 (C-1) borehole. In this study, we describe the chemical compositions of six melt samples over an approx. 40 m section of the core and compare them to previous melt samples from the Y-6 and C-1 boreholes.

Kring, David A.↗
NASA NTRS2003

Ocean Color and Evidence of Chlorophyll Signature in the TOMS Minimum Reflectivity Data

Analysis of the TOMS minimum reflectivity data for 380 nm channel (R380) show regions of high reflectivity values (approx. 7 to 8%) over Sargasso Sea in the Northern Atlantic, anti-cyclonic region in the Southern Atlantic, and a large part of the ocean in the Southern Pacific, and low values (5 approx. 6 %) over the rest of the open ocean. Through radiative transfer simulations we show that these features are highly correlated with the distribution of chlorophyll in the ocean. Theoretical minimum reflectivity values derived with the help of CZCS chlorophyll concentration data as input into a vector ocean-atmosphere radiative transfer code developed by Ahmad and Fraser show very good agreement with TOMS minimum reflectivity data for the winter season of year 1980. For the summer season of year 1980, good qualitative agreement is observed in the equatorial and northern hemisphere but not as good in the southern hemisphere. Also, for cloud-free conditions, we find a very strong correlation between R340 minus R380 values and the chlorophyll concentration in the ocean. Results on the possible effects of absorbing and non-absorbing aerosols on the TOMS minimum reflectivity will also be presented. The results also imply that ocean color will affect the aerosol retrieval over oceans unless corrected.

Ahmad, Z.↗
NASA NTRS2002

The Geometry of Resonant Signatures in Debris Disks with Planets

Using simple geometrical arguments, we paint an overview of the variety of resonant structures a single planet with moderate eccentricity (e<approx.0.6) can create in a dynamically cold, optically thin dust disk. This overview may serve as a key for interpreting images of perturbed debris disks and inferring the dynamical properties of the planets responsible for the perturbations. We compare the resonant geometries found in the solar system dust cloud with observations of dust clouds around Vega, Epsilon Eridani, and Fomalhaut.

Kuchner, Marc J.↗
NASA NTRS2001

Signature lipids and stable carbon isotope analyses of Octopus Spring hyperthermophilic communities compared with those of Aquificales representatives

The molecular and isotopic compositions of lipid biomarkers of cultured Aquificales genera have been used to study the community and trophic structure of the hyperthermophilic pink streamers and vent biofilm from Octopus Spring. Thermocrinis ruber, Thermocrinis sp. strain HI 11/12, Hydrogenobacter thermophilus TK-6, Aquifex pyrophilus, and Aquifex aeolicus all contained glycerol-ether phospholipids as well as acyl glycerides. The n-C(20:1) and cy-C(21) fatty acids dominated all of the Aquificales, while the alkyl glycerol ethers were mainly C(18:0). These Aquificales biomarkers were major constituents of the lipid extracts of two Octopus Spring samples, a biofilm associated with the siliceous vent walls, and the well-known pink streamer community (PSC). Both the biofilm and the PSC contained mono- and dialkyl glycerol ethers in which C(18) and C(20) alkyl groups were prevalent. Phospholipid fatty acids included both the Aquificales n-C(20:1) and cy-C(21), plus a series of iso-branched fatty acids (i-C(15:0) to i-C(21:0)), indicating an additional bacterial component. Biomass and lipids from the PSC were depleted in (13)C relative to source water CO(2) by 10.9 and 17.2 per thousand, respectively. The C(20-21) fatty acids of the PSC were less depleted than the iso-branched fatty acids, 18.4 and 22.6 per thousand, respectively. The biomass of T. ruber grown on CO(2) was depleted in (13)C by only 3.3 per thousand relative to C source. In contrast, biomass was depleted by 19.7 per thousand when formate was the C source. Independent of carbon source, T. ruber lipids were heavier than biomass (+1.3 per thousand). The depletion in the C(20-21) fatty acids from the PSC indicates that Thermocrinis biomass must be similarly depleted and too light to be explained by growth on CO(2). Accordingly, Thermocrinis in the PSC is likely to have utilized formate, presumably generated in the spring source region.

Carbon Isotopes/analysis↗
NASA NTRS1986

Quantum mechanical signature in exclusive coherent pion production

We calculate the coherent production of pions from subthreshold to relativistic energies in heavy-ion collisions using a quantum, microscopic, many-body model. For the first time, in this approach, we use harmonic oscillator wave functions to describe shell-model information. The theoretical quantum mechanical results obtained for the pion spectra represent an important improvement over our previous microscopic, many-body calculations.

NASA Discipline Radiation Health↗
NASA NTRS2004

A Deep Search with HST for Late Time Supernova Signatures in the Hosts of XRF 011030 and XRF 020427

X-ray Flashes (XRFs), are, like Gamma-Ray Bursts (GRBs) thought to signal the collapse of massive stars in distant galaxies. Many models posit that the isotropic equivalent energies of XRFs are lower than those for GRBs, such that they are visible hom a reduced range of distances when compared with GRBs. Here we present the results of two epoch Hubble Space Telescope imaging of two XRFs. These images taken approximately 45 and 200 days post bust reveal no evidence for an associated supernova in either case. Supernovae such as SN 1998bw would have been visible out to z approximately 1.5 in each case, while faint supernovae such as SN 2002ap would be visible to z approximately 1. At these distances the bursts would not fit the observed correlations between E(sub p) and E(sub iso) and would have required extremely luminous X-ray afterglows. We conclude that should these XRFs reside at low redshift, it is necessary either that their line of sight is heavily extinguished, or that XRFs, unlike GRBs do not have temporally coincident supernovae.

Patel, Sandeep↗
NASA NTRS2004

Signatures in Lightning Activity during Tennessee Valley Severe Storms of 5-6 May 2003

During the first week of May 2003, the Tennessee Valley experienced 14 tornadoes. Those that moved across the Tennessee Valley Region of northern Alabama and southern Tennessee provided an opportunity for study us- ing the North Alabama Lightning Mapping Array (LMA). On 5 May a classic supercell trekked across southern Tennessee spawning several tornadoes producing FO-F3 damage; on 6 May a high precipitation supercell moved across northern Alabama producing several FO-F1 tornadoes. The life cycle of these supercells will be discussed by presenting their electrical and radar evolution.

Gatlin, Patrick N.↗