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At least 109 records · Page 6
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NASA NTRS1998

Shock Modifications of Organic Compounds in Carbonaceous Chondrite Parent Bodies

Impacts among asteroidal objects would have altered or destroyed pre-existing organic matter in both targets and projectiles to a greater or lesser degree depending upon impact velocities. To begin filling a knowledge gap on the shock metamorphism of organic compounds, we are studying the effects of shock impacts on selected classes of organic compounds utilizing laboratory shock facilities. Our approach is to subject mixtures of organic compounds, embedded in the matrix of the Murchison meteorite, to simulated hypervelocity impacts by firing them into targets at various pressures. The mixtures are then analyzed to determine the amount of each compound that survives as well as to determine if new compounds are being synthesized. The initial compounds added to the matrix (with the exception of thiosulfate). The sulfonic acids were chosen in part because they are relatively abundant in Murchison, relatively stable, and because they and the phosphonic acids are the first well-characterized homologous series of organic sulfur and phosphorus compounds identified in an extraterrestrial material. Experimental procedures were more fully described in the original proposal. A 20 mm gun, with its barrel extending into a vacuum chamber (10(exp -2) torr), was used to launch the projectile containing the sample at approx. 1.6 km/sec (3,600 mi/hr) into the target material. Maximum pressure of impact depend on target/projectile materials. The target was sufficiently thin to assure minimum pressure decay over the total sample thickness.

Cooper, George W.↗
NASA NTRS1997

Cratering on Titan: A Pre-Cassini Perspective

The NASA-ESA Cassini mission, comprising a formidably instrumented orbiter and parachute-borne probe to be launched this October, promises to reveal a crater population on Titan that has been heretofore hidden by atmospheric haze. This population on the largest remaining unexplored surface in the solar system will be invaluable in comparative planetological studies, since it introduces evidence of the atmospheric effects of cratering on an icy satellite. Here, I highlight some impact features we may hope to find and could devote some modeling effort toward. Titan in a Nutshell: Radius= 2575 km. Density= 1880 kg/cubic m consistent with rock-ice composition. Surface pressure = 1.5 bar. Surface gravity = 1.35 m/square s Atmosphere -94% N2 6% CH, Surface temperature = 94K Tropopause temperature = 70K at 40 km alt. Probable liquid hydrocarbon deposits exist on or near the surface.Titan in a Nutshell: Radius= 2575 km. Density= 1880 kg/cubic m consistent with rock-ice composition. Surface pressure = 1.5 bar. Surface gravity = 1.35 m/square s; Atmosphere about 94% N2 6% CH, Surface temperature = 94K Tropopause temperature = 70K at 40 km alt. Probable liquid hydrocarbon deposits exist on or near the surface. Titan is comparable to Callisto and Ganymede for strength/gravity, Mars/Earth/Venus for atmospheric interaction, and Hyperion, Rhea, and Iapetus for impactor distribution. The leading/trailing asymmetry of crater density from heliocentric impactors is expected to be about 5-6, in the absence of resurfacing. Any Saturnocentric impactor population is likely to alter this. In particular the impact disruption of Hyperion is noted; because of the 3:4 orbital resonance with Titan, fragments from the proto-Hyperion breakup would have rapidly accreted onto Titan. Titan's resurfacing history is of course unknown. The disruption of impactors into fragments that individually create small craters is expected to occur. A crude estimate suggests a maximum separation of about 2 km (compared with 4 km on Venus, or 0.5 km on Earth). Crater chains are unlikely on Titan, since impactors must pass close enough to Saturn to be tidally disrupted; as a result, they would suffer aerodynamic disruption. Crater counting on adjacent satellites gives densities of about 200 per 10 (exp 6) square km for 20-km-diameter craters. However, the presence of a thick atmosphere leads to atmospheric shielding, depleting the relative abundance of small craters. This has been evaluated by models, and the relative abundance of small craters may be due to a diagnostic atmospheric collapse. A number of radar-dark "splotches" have been detected on Venus; these have been attributed to the interaction of the surface with the atmospheric shockwave produced by the Tunguska-like explosion of a bolide in the atmosphere. Simple analogy suggests that similar features might occur on Titan, but the shocked mass density (which controls the momentum coupling between the surface and the shockwave) of Titan's cold N2 atmosphere is about 20x smaller than that of Venus's hot CO2 atmosphere. Unless ice is much more easily turned to rubble than is rock, such features seem less probable on Titan. When the energy deposited by an impact forms a fireball with an equilibrate greater than one scale height, the fireball expands upward and can distribute ejecta. on ballistic exoatmospheric trajectories. On Venus this process is believed to be responsible for the parabolic features; the interaction of various-sized particles falling through the atmosphere with the zonal wind field winnows the particles to form a parabolic deposit. Although such a process is possible on Titan, the large scale height at higher altitudes would make it more difficult. Comparison with craters on other icy satellites suggests that craters on Titan will be fairly shallow (depth/diameter about 0.1) and craters greater than 10 km in diameter will have central peaks or domed bases, perhaps with central pits. The formation of ejecta. blankets may involve the atmosphere in a significant way, both by restraining the expansion of the ejecta cloud and by influencing the thermal history of the ejecta. Compared with Venus, Titan's atmosphere will chill an impact melt somewhat quickly, so the long ejecta flows seen on Venus seem less likely, detailed modeling needs to be performed to determine the impact melt production. Crater topography on Titan may be highlighted by the influence of liquids forming crater lakes. Craters with central peaks will typically form ring-shaped lakes, although horseshoe-shaped takes may be common; domed craters with central pits may even form bullseye lakes with islands with central ponds. If liquids have covered a substantial part of Titan's surface for a substantial period, hydroblemes and tsunami deposits may be common.

Lorenz, R. D.↗
NASA NTRS2004

Determination of Aromatic Ring Number Using Multi-Channel Deep UV Native Fluorescence

The in situ detection of organic material on an extraterrestrial surface requires both effective means of searching a relatively large surface area or volume for possible organic carbon, and a more specific means of identifying and quantifying compounds in indicated samples. Fluorescence spectroscopy fits the first requirement well, as it can be carried out rapidly, with minimal or no physical contact with the sample, and with sensitivity unmatched by any other organic analytical technique. Aromatic organic compounds with know fluorescence signatures have been identified in several extraterrestrial samples, including carbonaceous chondrites, interplanetary dust particles, and Martian meteorites. The compound distributions vary among these sources, however, with clear differences in relative abundances by number of aromatic rings and by degree of alkylation. This relative abundance information, therefore, can be used to infer the source of organic material detected on a planetary surface.

Bhartia, R.↗
NASA NTRS1985

Silicon to iron abundances in solar cosmic rays and in the sun

Differential spectra of even charged nuclei between Si and Fe in the August 4, 1972 event were made in the energy region of 10 to 40 MeV/n-1 using rocket borne plastic detectors. The resulting relative abundances of elements and low energy enhancements are obtained and compared with spectroscopically determined photospheric abundances. The implications of the relative abundances on the acceleration mechanisms is discussed.

Vahia, M. N.↗
NASA NTRS1972

Enrichment of very heavy nuclei in the composition of solar accelerated particles.

Measurement of the abundances of the nuclei C, N, O, Ne, Mg, Si, Ar, and Ca and the group Cr-Co relative to oxygen from seven solar energetic-particle events in the energy range from about 14 to 61 MeV per nucleon with a solid-state detector telescope on the OGO-5 satellite, 1968-1971. The differential energy spectra of O (14 to 29 MeV per nucleon) and Cr-Co (3 to 61 MeV per nucleon) have a spectral index of about (-3) for a power law in kinetic energy. The relative abundances of C, N, O, and Ne are in excellent agreement with emulsion studies. However, when compared with the solar photospheric and coronal abundances, the OGO-5 measurements show a large enhancement of relative abundances beginning with Si, and extending to the Cr-Co group. The enhancement over the solar and universal abundances is in rough agreement with the composition of the galactic cosmic radiation.

Mogro-Campero, A.↗
NASA NTRS1994

The composition of a coronal active region

The relative abundances of iron, oxygen, magnesium, and neon in a coronal active region are determined from measurements of soft X-ray line and broadband intensities. The emission measure, temperature, and column density are derived from these measured intensities and are used to place a constraint on the abundances of the heavier elements relative to hydrogen in the corona. The intensity measurements were made on 1987 December 11, when an active region was observed jointly by the American Science and Engineering (AS&E) High Resolution Soft X-Ray Imaging Sounding-Rocket Payload and the X-Ray Polychromator Flat Crystal Spectrometer (FCS) onboard the Solar Maximum Mission spacecraft. The coordinated observations include images through two broadband filters (8 to 29 A and 8 to 39, 44 to 60 A) and profiles of six emission lines: Fe XVII (15.01 A), FE VIII (15.26 A), O VIII (18.97 A), Mg XI (9.17 A), Ne IX (13.44 A), and Fe XVIII (14.21 A). The effects of resonance scattering are considered in the interpretation of the FCS line intensities. We calculated the expected intensity ratio of the two Fe XVII lines as a function of optical depth and compared this ratio with the observed intensity ratio to obtain the optical depths of each of the lines and the column density. The line intensities and the broadband filtered images are consistent with the emission from a thermal plasma where Fe, O, Mg, and Ne have the 'adopted coronal' abundances of Meyer (1985b) relative to one another, but are not consistent with the emission from a plasma having photospheric abundances: The ratios of the abundances of the low first ionization potential (FIP) elements (Fe and Mg) to the abundances of the high-FIP elements (Ne and O) are higher than the ratios seen in the photosphere by a factor of about 3.5. This conclusion is independent of the assumption of either an isothermal or a multithermal plasma. The column densities derived from the Fe XVII line ratio and the geometry of the active region provide a diagnostic of the abundance of hydrogen relative to the heavier elements. We find that the abundance of iron with respect to hydrogen in the corona is higher than the value given Meyer (1985b) by a factor of 8.2(-5.4, +5.1). This means that, for the observed active region, the absolute abundances of the low-FIP elements (Fe and Mg) are enhanced in the corona relative to the photosphere, while the abundances of the high-FIP elements (Ne and O) are either slightly enhanced in the corona or nearly the same in the photosphere and the corona.

Waljeski, K.↗
NASA NTRS2003

Platinum-group elements (PGE) and Rhenium in Marine Sediments across the Cretaceous-Tertiary Boundary: Constraints on Re-PGE Transport in the Marine Environment

The nature of Re-platinum-group element (PGE; Pt, Pd, Ir, Os, Ru) transport in the marine environment was investigated by means of marine sediments at and across the Cretaceous-Tertiary boundary (KTB) at two hemipelagic sites in Europe and two pelagic sites in the North and South Pacific. A traverse across the KTB in the South Pacific pelagic clay core found elevated levels of Re, Pt, Ir, Os, and Ru, each of which is approximately symmetrically distributed over a distance of approx. 1.8 m across the KTB. The Re-PGE abundance patterns are fractionated from chondritic relative abundances: Ru, Pt, Pd, and Re contents are slightly subchondritic relative to Ir, and Os is depleted by approx. 95% relative to chondritic Ir proportions. A similar depletion in Os (approx. 90%) was found in a sample of the pelagic KTB in the North Pacific, but it is enriched in Ru, Pt, Pd, and Re relative to Ir. The two hemipelagic KTB clays have near-chondritic abundance patterns. The approx. 1.8-m-wide Re-PGE peak in the pelagic South Pacific section cannot be reconciled with the fallout of a single impactor, indicating that postdepositional redistribution has occurred. The elemental profiles appear to fit diffusion profiles, although bioturbation could have also played a role. If diffusion had occurred over approx. 65 Ma, the effective diffusivities are approx. 10(exp -13)sq cm/s, much smaller than that of soluble cations in pore waters (approx. 10(exp -5) sq cm/s). The coupling of Re and the PGEs during redistribution indicates that postdepositional processes did not significantly fractionate their relative abundances. If redistribution was caused by diffusion, then the effective diffusivities are the same. Fractionation of Os from Ir during the KTB interval must therefore have occurred during aqueous transport in the marine environment. Distinctly subchondritic Os/Ir ratios throughout the Cenozoic in the South Pacific core further suggest that fractionation of Os from Ir in the marine environment is a general process throughout geologic time because most of the inputs of Os and Ir into the ocean have OsAr ratios greater than or = 1. Mass balance calculations show that Os and Re burial fluxes in pelagic sediments account for only a small fraction of the riverine Os (less than 10%) and Re (less than 0.1%) inputs into the oceans. In contrast, burial of Ir in pelagic sediments is similar to the riverine Ir input, indicating that pelagic sediments are a much larger repository for Ir than for Os and Re. If all of the missing Os and Re is assumed to reside in anoxic sediments in oceanic margins, the calculated burial fluxes in anoxic sediments are similar to observed burial fluxes. However, putting all of the missing Os and Re into estuarine sediments would require high concentrations to balance the riverine input and would also fail to explain the depletion of Os at pelagic KTB sites, where at most approx. 25% of the K-T impactor's Os could have passed through estuaries. If Os is preferentially sequestered in anoxic marine environments, it follows that the OsAr ratio of pelagic sediments should be sensitive to changes in the rates of anoxic sediment deposition. There is thus a clear fractionation of Os and Re from Ir in precipitation out of sea water in pelagic sections. Accordingly, it is inferred here that Re and Os are removed from sea water in anoxic marine depositional regimes.

Lee, Cin-Ty Aeolus↗
NASA NTRS2013

Galactic Cosmic-Ray Energy Spectra and Composition during the 2009-2010 Solar Minimum Period

We report new measurements of the elemental energy spectra and composition of galactic cosmic rays during the 2009-2010 solar minimum period using observations from the Cosmic Ray Isotope Spectrometer (CRIS) onboard the Advanced Composition Explorer. This period of time exhibited record-setting cosmic-ray intensities and very low levels of solar activity. Results are given for particles with nuclear charge 5 <= Z <= 28 in the energy range approx. 50-550 MeV / nucleon. Several recent improvements have been made to the earlier CRIS data analysis, and therefore updates of our previous observations for the 1997-1998 solar minimum and 2001-2003 solar maximum are also given here. For most species, the reported intensities changed by less than approx. 7%, and the relative abundances changed by less than approx. 4%. Compared with the 1997-1998 solar minimum relative abundances, the 2009-2010 abundances differ by less than 2sigma, with a trend of fewer secondary species observed in the more recent time period. The new 2009-2010 data are also compared with results of a simple "leaky-box" galactic transport model combined with a spherically symmetric solar modulation model. We demonstrate that this model is able to give reasonable fits to the energy spectra and the secondary-to-primary ratios B/C and (Sc+Ti+V)/Fe. These results are also shown to be comparable to a GALPROP numerical model that includes the effects of diffusive reacceleration in the interstellar medium.

Galactic Cosmic Rays↗
NASA NTRS1972

Surface composition of magnetic neutron stars.

The relative abundances of seven constituent nuclei, He4, C12, O16, Ne20, Mg24, Si28, and Fe56, are calculated as a function of time for neutron star atmospheres within which exist magnetic fields of the order of 10 to the 13th G. The opacity, equation of state of the electrons, and cooling rate of the magnetic star are discussed, and it is shown to be a reasonable approximation to assume an atmosphere to be isothermal. The effects of particle diffusion are included in the nuclear reaction network. Computations are performed both for a constant mass atmosphere and for an atmosphere in which mass is being ejected. It is found that the final abundances are model-independent, as long as the initial model contains predominantly He4. The relative abundances are compared to the cosmic ray spectrum. For both the constant-mass and mass-loss atmospheres, nucleosynthesis proceeds virtually completely to Fe56. However the outermost layers of the envelope, in which no mass is being ejected, are composed almost entirely of He4 with trace amounts of Fe56. After the loss of about 10 to the 21st g, only Fe56 is ejected from atmospheres expelling mass.

Rosen, L. C.↗
NASA NTRS1991

Abundance variations in solar active regions

The diversity in the published values of coronal abundances is unsettling, especially as the range of results seems to be beyond the quoted uncertainties. Measurements of the relative abundance of iron and neon derived from soft X-ray spectra of active regions are presented. From a data base of over 200 spectra taken by the Solar Maximum Mission Flat Crystal Spectrometer, it is found that the relative abundance can vary by as much as a factor of about 7 and can change on timescales of less than 1 h.

Strong, K. T.↗
NASA NTRS1988

On the origin of Venus' atmosphere - Possible contributions from simple component mixtures and fractionated solar wind

It is suggested that while an origin of the volatiles of the Venus atmosphere as a single, fractionated component derivable from the solar wind can account for Ar, Kr, and Xe relative abundances, it does so only with an excess of C, and perhaps of N. A similarity is noted in relative abundances between Venus volatiles and fractionated solar wind gases in the lunar regolith which implies that such a lunar-type component is a major contributor to Venus' volatiles. A variety of Venus atmosphere models is considered; these fail to explain the low Ne/Ar ratio on Venus.

Bogard, Donald D.↗
NASA NTRS1994

Noble gases in presolar diamonds II: Component abundances reflect thermal processing

Using the isotopic compositions derived in Huss and Lewis, 1994a, abundances of the P3, HL, and P6 noble-gas components were determined for 15 diamonds separates from primitive chondrites of 8 chondrite classes. Within a meteorite class, the relative abundances of these components correlate with the petrologic subtype of the host meteorite, indicating that metamorphism is primarily responsible for the variations. Relative abundances of P3, HL, and P6 among diamond samples can be understood in terms of thermal processing of a single mixture of diamonds like those now found in CI and CM2 chondrites. With relatively gentle heating, primitive diamonds first lose their low-temperature P3 gases and a 'labile' fraction of the HL component. Mass loss associated with release of these components produces an increase in the HL and P6 content of the remaining diamond relative to unprocessed diamond. Higher temperatures initiate destruction of the main HL carrier, while the HL content of the surviving diamonds remains essentially constant. At the same time, the P6 carrier begins to preferentially lose light noble gases. Meteorites that have experienced metamorphic temperatures greater than or = 650 C have lost essentially all of their presolar diamond through chemical reactions with surrounding minerals. The P3 abundance seems to be a function only of the maximum temperature experienced by the diamonds and thus is independent of the nature of the surrounding environment. If all classes inherited the same mixture of primitive diamonds, then P3 abundances would tie together the metamorphic scales in different meteorite classes. However, if the P3 abundance indicates a higher temperature than do other thermometers applicable to the host meteorite, then the P3 abundance may contain information about heating prior to accretion. Diamonds in the least metamorphosed EH, CV, and CO chondrites seem to carry a record of pre-accretionary thermal processing.

Huss, Gary R.↗
NASA NTRS1993

Planetary and satellite x ray spectroscopy: A new window on solid-body composition by remote sensing

The rings and most of the satellites of the outer planets orbit within the radiation belts of their parent bodies. This is an environment with intense fluxes of energetic electrons. As a result, these objects are strong emitters of X-rays. The characteristic X-ray lines from these bodies depend on atomic composition, but they are not sensitive to how the material is arranged in compounds or mixtures. X-ray fluorescence spectral analysis has demonstrated its unique value in the laboratory as a qualitative and quantitative analysis tool. This technique has yet to be fully exploited in a planetary instrument for remote sensing. The characteristic X-ray emissions provide atomic relative abundances. These results are complementary to the molecular composition information obtained from IR, visible, and UV emission spectra. The atomic relative abundances are crucial to understanding the formation and evolution of these bodies. They are also crucial to the proper interpretation of the molecular composition results from the other sensors. The intensities of the characteristic X-ray emissions are sufficiently strong to be measured with an instrument of modest size. Recent developments in X-ray detector technologies and electronic miniaturization have made possible space-flight X-ray imaging and nonimaging spectrometers of high sensitivity and excellent energy resolution that are rugged enough to survive long-duration space missions. Depending on the application, such instruments are capable of resolving elemental abundances of elements from carbon through iron. At the same time, by measuring the bremsstrahlung intensity and energy spectrum, the characteristics of the source electron flux can be determined. We will discuss these concepts, including estimated source strengths, and will describe a small instrument capable of providing this unique channel of information for future planetary missions. We propose to build this instrument using innovative electronics packaging methods to minimize size and weight.

Chenette, D. L.↗
NASA NTRS1997

Studies for the Loss of Atomic and Molecular Species from Io

The general objective of this project is to advance our theoretical understanding of Io's atmosphere by studying how various atomic and molecular species are lost from this atmosphere and are distributed near the satellite and in the circumplanetary environment of Jupiter. The project is divided into well-defined studies described for the likely dominant atmospheric gases involving species of the SO2 family (SO2, SO, 02, 0, S) and for the trace atmospheric gas atomic sodium. The relative abundance of the members of the S02 family and Na (and its parent Na(x)) at the satellite exobase and their relative spatial densities beyond in the extended corona of lo are not well known but will depend upon a number of factors including the upward transport rate of gases from below, the velocity distribution and corresponding escape rate of gases at the exobase, and the operative magnetospheric/solar-photon driven chemistry for the different gases. This question of relative abundance will be studied in this project.

Smyth, William H.↗
NASA NTRS2001

Sensing, Spectra and Scaling: What's in Store for Land Observations

Bill Pecora's 1960's vision of the future, using spacecraft-based sensors for mapping the environment and exploring for resources, is being implemented today. New technology has produced better sensors in space such as the Landsat Thematic Mapper (TM) and SPOT, and creative researchers are continuing to find new applications. However, with existing sensors, and those intended for launch in this century, the potential for extracting information from the land surface is far from being exploited. The most recent technology development is imaging spectrometry, the acquisition of images in hundreds of contiguous spectral bands, such that for any pixel a complete reflectance spectrum can be acquired. Experience with Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) has shown that, with proper attention paid to absolute calibration, it is possible to acquire apparent surface reflectance to 5% accuracy without any ground-based measurement. The data reduction incorporates in educated guess of the aerosol scattering, development of a precipitable water vapor map from the data and mapping of cirrus clouds in the 1.38 micrometer band. This is not possible with TM. The pixel size in images of the earth plays and important role in the type and quality of information that can be derived. Less understood is the coupling between spatial and spectral resolution in a sensor. Recent work has shown that in processing the data to derive the relative abundance of materials in a pixel, also known is unmixing, the pixel size is an important parameter. A variance in the relative abundance of materials among the pixels is necessary to be able to derive the endmembers or pure material constituent spectra. In most cases, the 1 km pixel size for the Earth Observing System Moderate Resolution Imaging Spectroradiometer (MODIS) instrument is too large to meet the variance criterion. A pointable high spatial and spectral resolution imaging spectrometer in orbit will be necessary to make the major next step in our understanding of the solid earth surface and its changing face.

Goetz, Alexander F. H.↗
NASA NTRS2021

Investigation on the Origins of Comets as Revealed through IR High Resolution Spectroscopy: I. Molecular Abundances

We report and analyze molecular abundances updatedin twenty comets by employingmodern data reduction procedures and molecular models. Using boxplots and scatterplots, we examine how the different molecular species are distributed among the comet population, while by means of pie charts we investigate the relative proportions of these molecular species in each comet. We compare these results with the orbital parametersof the selected targets in order to identify trends related to the dynamical history of each comet. In this way, we identify at least three chemical classes based mainly on relative abundances of CO, CH3OH, CH4, C2H6, HCN and NH3. The combination of relative abundances and orbital parameters is then compared with chemical models of planetary system formation and may offer an alternative approach to investigate the origin and evolution of the material in cometary nuclei.Our study also confirms the need to add more objects to our sample in order to improve the statistics, especially for hyper-volatiles (i.e. CH4and CO) in Jupiter Family comets.

M Lippi↗
NASA NTRS1986

The abundance and relative volatility of refractory trace elements in Allende Ca,Al-rich inclusions - Implications for chemical and physical processes in the solar nebula

The relative volatilities of lithophile refractory trace elements (LRTE) were determined using calculated 50-percent condensation temperatures. Then, the refractory trace-element abundances were measured in about 100 Allende inclusions. The abundance patterns found in Allende Ca,Al-rich inclusions (CAIs) and ultrarefractory inclusions were used to empirically modify the calculated LRTE volatility sequence. In addition, the importance of crystal-chemical effects, diffusion constraints, and grain transport for the origin of the trace-element chemistry of Allende CAIs (which have important implications for chemical and physical processes in the solar nebula) is discussed.

Kornacki, Alan S.↗