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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
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NASA NTRS1995

Interstellar Dust Connections to Interplanetary Dust

The organic component of the interstellar medium, which has revealed itself through the ubiquitous 3.4 micrometer hydrocarbon absorption feature, is widespread throughout the disk of our galaxy and has been attributed to dust grains residing in the diffuse interstellar medium. The absorption band positions near 3.4 micrometers are characteristic of C-H stretching vibrations in the -CH3 and -CH2- groups of saturated aliphatic hydrocarbons associated with perturbing chemical groups. The production of complex molecules is thought to occur within dense molecular clouds when ice- mantled grains are processed by various energetic mechanisms. Studies of the processing of interstellar ices and the subsequent production of organic residues have relevance to studies of interplanetary dust, because primitive solar system bodies are likely reservoirs of organic material, either preserved from the interstellar medium or produced in situ. A comparison of the interstellar organics and the Murchison meteorite illustrates the importance of probing the interstellar connection to the solar system, because although the carbonaceous meteorites are undoubtedly highly processed, they do retain specific interstellar signatures (such as diamonds, SiC grains, graphite and enriched D/H). The organic component, while not proven interstellar, has a remarkable similarity to the interstellar organics observed in over a dozen sightlines through our galaxy. This paper compares spectra from laboratory organics produced through the processing of interstellar ice analog materials with the high resolution infrared observations of the interstellar medium in order to investigate the mechanisms (such as ion bombardment, plasma processing, and UV photolysis) that may be producing the organics in the ISM. Comparisons to interplanetary dust particles, comets, and meteorites are discussed.

Pendleton, Y. J.↗
NASA NTRS2010

Isotopic Fractionation in Comets: Quantifying the Contribution of Interstellar Chemistry

Anomalously fractionated isotopic material is found in many primitive Solar System objects, such as meteorites and comets. It is thought, in some cases, to trace interstellar matter that was incorporated into the Solar Nebula without undergoing significant processing. We will present the results of models of the nitrogen, oxygen, and carbon fractionation chemistry in dense molecular clouds, particularly in cares where substantial freeze-taut of molecules on to dust has occurred. The range of fractionation ratios expected in different interstellar molecules will be discussed and compared to the ratios measured in molecular clouds, comets and meteoritic material. These models make several predictions that can be tested in the near future by molecular line observations, particularly with the GBT.

Charnley, Steven↗
NASA NTRS2011

Isotope Fractionation in the Interstellar Medium

Anomalously fractionated isotopic material is found in many primitive Solar System objects, such as meteorites and comets. It is thought, in some cases, to trace interstellar matter that was incorporated into the Solar Nebula without undergoing significant processing. We will present the results of models of the nitrogen, oxygen, and carbon fractionation chemistry in dense molecular clouds, particularly in cores where substantial freeze-out of molecules on to dust has occurred. The range of fractionation ratios expected in different interstellar molecules will be discussed and compared to the ratios measured in molecular clouds, comets and meteoritic material. These models make several predictions that can be tested in the near future by molecular line observations, particularly with ALMA.

Charnley, Steven↗
NASA NTRS2004

Insight into Primordial Solar System Oxygen Reservoirs from Returned Cometary Samples

The recent successful rendezvous of the Stardust spacecraft with comet Wild-2 will be followed by its return of cometary dust to Earth in January 2006. Results from two separate dust impact detectors suggest that the spacecraft collected approximately the nominal fluence of at least 1,000 particles larger than 15 micrometers in size. While constituting only about one microgram total, these samples will be sufficient to answer many outstanding questions about the nature of cometary materials. More than two decades of laboratory studies of stratospherically collected interplanetary dust particles (IDPs) of similar size have established the necessary microparticle handling and analytical techniques necessary to study them. It is likely that some IDPs are in fact derived from comets, although complex orbital histories of individual particles have made these assignments difficult to prove. Analysis of bona fide cometary samples will be essential for answering some fundamental outstanding questions in cosmochemistry, such as (1) the proportion of interstellar and processed materials that comprise comets and (2) whether the Solar System had a O-16-rich reservoir. Abundant silicate stardust grains have recently been discovered in anhydrous IDPs, in far greater abundances (200 5,500 ppm) than those in meteorites (25 ppm). Insight into the more subtle O isotopic variations among chondrites and refractory phases will require significantly higher precision isotopic measurements on micrometer-sized samples than are currently available.

Brownlee, D. E.↗
NASA NTRS1996

Detection of acetylene in the infrared spectrum of comet Hyakutake

Comets are rich in volatile materials, of which roughly 80% (by number) are water molecules. Considerable progress is being made in identifying the other volatile species, the abundances of which should enable us to determine whether comets formed primarily from ice-covered interstellar grains, or from material that was chemically processed in the early solar nebula. Here we report the detection of acetylene (C2H2) in the infrared spectrum of comet C/1996 B2 (Hyakutake). The estimated abundance is 0.3-0.9%, relative to water, which is comparable to the predicted solid-phase abundance in cold interstellar clouds. This suggests that the volatiles in comet Hyakotake may have come from ice-covered interstellar grains, rather than material processed in the accretion disk out of which the Solar System formed.

Acetylene/analysis↗
NASA NTRS2001

Far Ultraviolet Spectroscopy of the Intergalactic and Interstellar Absorption Toward 3C 273

We present Far Ultraviolet Spectroscopic Explorer observations of the molecular, neutral atomic, weakly ionized, and highly ionized components of the interstellar and intergalactic material toward the quasar 3C273. We identify Ly-beta absorption in eight of the known intergalactic Ly-alpha absorbers along the sight line with the rest-frame equivalent widths W(sub r)(Ly-alpha) > 50 micro-angstroms. Refined estimates of the H(I) column densities and Doppler parameters (b) of the clouds are presented. We find a range of b = 16-46 km/s. We detect multiple H(I) lines (Ly-beta - Ly-theta) in the 1590 km/s Virgo absorber and estimate logN(H(I)) = 15.85 +/- 0.10, ten times more H(I) than all of the other absorbers along the sight line combined. The Doppler width of this absorber, b = 16 km/s, implies T < 15,000 K. We detect O(VI) absorption at 1015 km/s at the 2-3(sigma) level that may be associated with hot, X-ray emitting gas in the Virgo Cluster. We detect weak C(III) and O(VI) absorption in the IGM at z=0.12007; this absorber is predominantly ionized and has N(H+)/N(H(I)) > 4000/Z, where Z is the metallicity. Strong Galactic interstellar O(VI) is present between -100 and +100 km/s with an additional high-velocity wing containing about 13% of the total O(VI) between +100 and +240 km/s. The Galactic O(VI), N(V), and C(IV) lines have similar shapes, with roughly constant ratios across the -100 to +100 km/s velocity range. The high velocity O(VI) wing is not detected in other species. Much of the interstellar high ion absorption probably occurs within a highly fragmented medium within the Loop IV remnant or in the outer cavity walls of the remnant. Multiple hot gas production mechanisms are required. The broad O(VI) absorption wing likely traces the expulsion of hot gas out of the Galactic disk into the halo. A flux limit of 5.4 x 10(epx -16) erg/sq cm/s on the amount of diffuse O(VI) emission present = 3.5' off the 3C273 sight line combined with the observed O(VI) column density toward 3C273, logN O(VI) = 14.73 +/- 0.04, implies n(sub e) < 0.02/cubic cm and P/k < 11,500/cubic cm for an assumed temperature of 3 x 10(exp 5) K. The elemental abundances in the neutral and weakly-ionized interstellar clouds are similar to those found for other halo clouds. The warm neutral and warm ionized clouds along the sight line have similar dust-phase abundances, implying that the properties of the dust grains in the two types of clouds are similar. Interstellar H2 absorption is present at positive velocities at a level of logN(H2) = 15.71, but is very weak at the velocities of the main column density concentration along the sight line observed in H(I) 21 cm emission.

Sembach, Kenneth R.↗
NASA NTRS1995

Processing Mechanisms for Interstellar Ices: Connections to the Solar System

The organic component of the interstellar medium, which has revealed itself through the ubiquitous 3.4 micrometers hydrocarbon absorption feature, is widespread throughout the disk of our galaxy and has been attributed to dust grains residing in the diffuse interstellar medium. The absorption band positions near 3.4 micrometers are characteristic of C-H stretching vibrations in the -CH3 and -CH2- groups of saturated aliphatic hydrocarbons associated with perturbing chemical groups. The production of complex molecules is thought to occur within dense molecular clouds when ice-mantled grains are processed by various energetic mechanisms. Studies of the processing of interstellar ices and the subsequent production of organic residues have relevance to studies of ices in the solar system, because primitive, icy solar system bodies such as those in the Kuiper belt are likely reservoirs of organic material, either preserved from the interstellar medium or produced in situ. Connections between the interstellar medium and the early solar nebula have long been a source of interest. A comparison of the interstellar organics and the Murchison meteorite illustrates the importance of probing the interstellar connection to the solar system, because although the carbonaceous meteorites are undoubtedly highly processed, they do retain specific interstellar signatures (such as diamonds, SiC grains, graphite and enriched D/H). The organic component, while not proven interstellar, has a remarkable similarity to the interstellar organics observed in over a dozen sightlines through our galaxy. This paper compares spectra from laboratory organics produced through the processing of interstellar ice analog materials with the high resolution infrared observations of the interstellar medium in order to investigate the mechanisms (such as ion bombardment, plasma processing, and UV photolysis) that may be producing the organics in the ISM.

Pendleton, Y. J.↗
NASA NTRS2000

The Composition of Organics and Volatiles in the Interstellar Medium

Tremendous progress has been made in our understanding of the composition of interstellar dust through the combined use of telescopic observations, theoretical models, laboratory studies of analogs, and the analysis of interstellar samples found in meteorites. It is increasingly clear that the interstellar medium (ISM) contains an enormous diversity of materials created by a wide range of chemical and physical processes. This paper reviews some of our current knowledge of the organic and volatile materials thought to exist in the ISM. These compounds supply a significant portion of the material that makes up the interstellar dense molecular clouds from which new stars and planetary systems are formed, and thus represents an important reservoir of material that could play key roles in the formation and evolution of life. This paper will largely focus on solid materials, as opposed to gases, since solids contain a major fraction of the heavier elements in clouds and because solids are most likely to survive incorporation into new planetary systems in identifiable form. The paper concludes with a brief discussion of the astrobiological relevance of some of the compounds now known or suspected to be present in the ISM.

Sandford, Scott A.↗
NASA NTRS2003

The Stardust solar array

The Stardust program, part of NASA's Discovery Missions was launched on February 7. 1999. It's seven-year mission is to gather interstellar dust and material from the comet Wild-2 and return the material to earth in January 2006. In order to accomplish this mission, the satellite will orbit the sun a total of three times, traversing distances from a little under 1 AU to 2.7 AU. On April 18 2002 , the Stardust spacecraft reached its furthest distance and broke the record for being the farthest spacecraft from the sun powered by solar energy, The Stardust solar panels were built with standard off the shelf 10 Ohm-cm high efficiency silicon solar cells. These solar cells are relatively inexpensive and have shown excellent characteristics under LILT conditions. In order to accommodate the varying temperature and intensity conditions on the electrical power subsystem, an electronic switch box was designed to reconfigure the string length and number of swings depending on the mission phase. This box allowed the use of an inexpensive direct energy transfer system for the electrical power system architecture. The solar panels and electrical power system have met all requirements. Telemetry data from the solar panels at 2.7 AU are in excellent agreement with flight predictions.

Stardust interstellar dust Wild-2 solar panels sol↗
NASA NTRS1975

The role of dust in cosmogony

A discussion is given of the production of interstellar grain cores from stellar material, the gain and loss of grain mantles in interstellar space, chemical transformations in these grains when they become part of the primitive solar nebula, and the identification of these grains with interplanetary dust derived from comets and with the matrix material in meteorites. Thus, this paper proposes a common cosmogonic framework relating studies of interstellar and interplanetary grains.

Cameron, A. G. W.↗
NASA NTRS1975

Measurement of primary cosmic-ray electrons and positrons from 4 to 50 GeV

We have used a bremsstrahlung-identification technique to measure electron and positron spectra in the primary cosmic rays from 4 to 50 GeV. Above our average geomagnetic cutoff of 4.0 GV/c, we find fluxes of 4.4 (plus or minus 0.3) electrons and 0.37 (plus or minus 0.09 positrons) per sq m/sr/sec. The electron events follow a differential power law whose spectral index is 2.8 (plus or minus 0.1). Our ratio electrons/(electrons + positrons) = 0.08 (plus or minus 0.02) implies traversal of an equivalent slab thickness of 4.3 (plus or minus 1.5) g/sq cm of interstellar and source material.

Buffington, A.↗
NASA NTRS1980

Superposition of supernovae remnant imagery

The superposition of the X-ray, optical, and radio imagery of supernova remnants in the Cygnus Loop region is described. The radio data of the region was obtained using the Westerbork interferometer, and the optical image was recorded by the NASA Wide Field Camera. The X-ray imagery was obtained using the High Resolution Imager. The mechanisms by which the supernova ejecta and the swept-up material shock the interstellar medium are studied by the resampling of the imagery onto a common celestial grid. The initial results indicate a radio arc in the northeastern portion of the region that is along the faintest outermost filaments, and a separate radio arc along the brightest filaments.

Henden, A. A.↗
NASA NTRS1986

Observational constraints on circumstellar dust

There is an enormous range in the properties of stars that are losing mass. The red giants responsible for injecting roughly half or more of the material into the interstellar medium are reviewed. The physical properties are described for the out flowing gases. Broadband observation constaints on the dust are described by use of spectrum analysis. Circumstellar dust is identified by carbon-carbon and carbon-hydrogen bonds.

Jura, M.↗
NASA NTRS1995

Are Unidentified Extreme-Ultraviolet Sources the Closest Neutron Stars?

Unidentified extreme-ultraviolet (EUV) sources, detected in the EUVE and ROSAT WFC all-sky surveys, could be isolated old neutron stars, accreting material from the interstellar medium (ISM). The closest neutron stars, which are located in the local ISM bubble of unusually low density, are faint and cool (L approximately 10(exp 27) erg/s, T approximately < 6 eV). The extreme-UV spectrum of these sources is very sensitive to the H I column density, since a large fraction of the energy is emitted just below the hydrogen Lyman edge. The EUVE sources with large count rates in the long-wavelength bandpass (600 A) seem to be the most promising candidates. These sources should have low H I column density (N(sub H I) approximately < 10(exp 18) sq cm), constraining their distances to a few tens of parsecs. Otherwise, their spectra would be significantly modified by ISM absorption, and inevitably they would appear stronger in the short-wavelength (100 A, 200 A) EUVE bandpasses. If these unidentified objects are familiar EUV sources rather than neutron stars, i.e. white dwarfs, late-type stars or cataclysmic variables, they are expected to be identifiable, and generally brighter than V approximately 14.

Shemi, A.↗
NASA NTRS2002

Side Group Addition to the PAH Coronene by UV Photolysis in Cosmic Ice Analogs

Ultraviolet photolysis of various ice mixtures at low temperature and pressure caused the addition of amino (-NH2), methyl (-CH3), methoxy (-OCH3), and cyano (-CN) functional groups to the polycyclic aromatic hydrocarbon (PAH) coronene (C22H12). The implications of these results for interstellar and meteoritic chemistry are discussed. Previously only simple PAH photo-oxidation had been reported. This work represents the first experimental evidence that ice photochemistry may have contributed to aromatics bearing carbon and nitrogen containing side groups that are detected in primitive meteorites and interplanetary dust particles. Furthermore, these results suggest a wider range of modified PAHs should be expected in interstellar lees and materials predating solar system formation.

Bernstein, Max P.↗
NASA NTRS2003

Formation and Survival of Amino Acids in Space

The detection of deuterium enrichments in meteoritic hydroxy and amino acids demonstrates that there is a connection between organic material in the interstellar medium and in primitive meteorites. It has generally been assumed that such molecules formed via reactions of small deuterium enriched insterstellar precursors in liquid water on a large asteroidal or cometary parent body. We have recently show that the W photolysis of interstellar/presolar ices can produce the amino acids alanine, serine, and glycine, as well as hydroxy acids, and glycerol, all of which have been extracted from the Murchison meteorite. Thus, some of the probiologically interesting organic compounds, compounds found in meteorites may have formed in presolar ice and have not solely been a product of parent body liquid water chemistry. We will report on our isotopic labeling studies of the mechanism of formation of these interesting compounds, and on astrophysically relevant kinetic studies UV photodecomposition of amino acid precursors in the solid state. This is our first year of exobiology funding on this project.

Bernstein, M. P.↗
NASA NTRS2003

Formation and Survival of Amino Acids in Space

The detection of deuterium enrichments in meteoritic hydroxy and amino acids demonstrates that there is a connection between organic material in the interstellar medium and in piimitive meteorites. It has generally been assumed that such molecules formed via reactions of small deuterium enriched insterstellar precursors in liquid water on a large asteroidal or cometary parent body. We have recently show that the W photolysis of interstellar/presolar ices can produce the amino acids alanine, serine, and glycine, as well as hydroxy acids, and glycerol, all of which have been extracted from the Murchison meteorite. Thus, some of the probiologically interesting organic compounds compounds found in meteorites may have formed in presolar ice and have not solely been a product of parent body liquid water chemistry. We will report on our isotopic labeling studies of the mechanism of formation of these inteiesting compounds, and on astrophysically relevant kinetic studies UV photo-decomposition of amino acid precursors in the solid state. This is our first year of exobiology funding on this project.

Bernstein, M. P.↗
NASA NTRS2018

A Deep X-Ray View of the Synchrotron-Dominated Supernova Remnant G330.2+1.0

We present moderately deep (125 ks) XMM-Newton observations of supernova remnant G330.2+1.0. This remnant is one of only a few known that fall into the "synchrotron-dominated" category, with the emission almost entirely dominated by a nonthermal continuum. Previous X-ray observations could only characterize the spectra of a few regions. Here, we examine the spectra from 14 regions surrounding the entire rim, finding that the spectral properties of the nonthermal emission do not vary significantly in any systematic way from one part of the forward shock to another, unlike several other remnants of this class. We confirm earlier findings that the power-law index, Γ, ranges from about 2.1-2.5, while the absorbing column density is generally between (2.0-2.6) × 10(exp 22) cm(exp -2). Fits with the srcut model find values of the roll-off frequency in the range of 10(exp 17.1)-10(exp 17.5) Hz, implying energies of accelerated electrons of approximately 100 TeV. These values imply a high shock velocity of approximately 4600 km s(exp -1), favoring a young age of the remnant. Diffuse emission from the interior is nonthermal in origin as well, and fits to these regions yield similar values to those along the rim, also implying a young age. Thermal emission is present in the east, and the spectrum is consistent with approximately 650 km s(exp -1) shock wave encountering interstellar or circumstellar material with a density of approximately 1 cm(exp -3).

Williams, Brian J.↗