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NASA NTRS1978

Rare-earth abundances in chondritic meteorites

Fifteen chondrites, including eight carbonaceous chondrites, were analyzed for rare earth element abundances by isotope dilution. Examination of REE for a large number of individual chondrites shows that only a small proportion of the analyses have flat unfractionated REE patterns within experimental error. While some of the remaining analyses are consistent with magmatic fractionation, many patterns, in particular those with positive Ce anomalies, can not be explained by known magmatic processes. Elemental abundance anomalies are found in all major chondrite classes. The persistence of anomalies in chondritic materials relatively removed from direct condensational processes implies that anomalous components are resistant to equilibrium or were introduced at a late stage of chondrite formation. Large-scale segregation of gas and condensate is implied, and bulk variations in REE abundances between planetary bodies is possible.

Evensen, N. M.↗
NASA NTRS1985

Chemical-dynamical models of the Venus mesosphere based upon diurnal microwave CO variations

An attempt is made to explain the fact that the large variation in Venus CO abundance with planetary phase using a combination of photochemical and kinematical models. Present knowledge about the Venus mesosphere is first summarized, emphasizing the more completely measured lower and upper atmosphere. The predictions of Dickinson and Ridley's (1977) hydrodynamic modeling are compared to the results of microwave observations of CO. It is noted that the nightside CO bulge above 90-95 km altitude indicated by microwave measurements is a primary characteristic of these models, whereas the opposite phase behavior of CO between 80 and 90 km is not predicted by them. The result of diurnal photochemical models for the Venus mesosphere are presented and an attempt is made to reproduce the phase behavior of CO between 80 and 90 km in the Venus mesosphere. Possible diurnal variations due to chemistry and vertical eddy diffusion are considered.

Clancy, R. T.↗
NASA NTRS1989

Abundance of condensable species at planetary cold traps - The role of moist convection

The interplay of moist convection and particle growth in the tropopause region of the atmospheres of earth, Uranus, and Neptune has been investigated. It is found that the downward flux of aerosols is not sufficient to dehydrate the earth's stratosphere by chemical dessication, and that the source of Neptune's oversaturated stratosphere is convective penetration of the tropopause by moist convective columns of methane. It is shown that conditions in the troposphere of Uranus are not conducive to the initiation of moist convection.

Lunine, Jonathan I.↗
NASA NTRS1981

The abundances of neon, sulfur, and argon in planetary nebulae

New infrared observations of Ne II, Ar III, and S IV are used in optical observations of other ionization states of the considered elements to evaluate the abundances of neon, argon, and sulfur in 18 planetary nebulae. Attention is also given to one or more of the infrared lines in 18 other nebulae. It is pointed out that S IV was detected in approximately 90% of the observed objects, while Ar III was found in about 80%, and Ne II in roughly one-third. It is noted that optical observations typically include only a limited region of the nebula, while the infrared measurements frequently involve integration over the entire nebular image.

Beck, S. C.↗
NASA NTRS1978

The distribution of S IV and Ne II in NGC 7027

Results are reported for measurements of the S IV 10.5-micron and Ne II 12.8-micron IR emission lines at four positions in NGC 7027 and of the Ar III 9.0-micron line at one position in the same planetary nebula. Ionic abundances are calculated using the data obtained at one position and are combined with published optical data for other ionization states to obtain total elemental abundances. The S IV and Ne II line-intensity distributions are compared with an 8.1-GHz radio map of the nebula. The S IV distribution indicates a density of about 500,000 per cu cm, and the Ne II is found to be contained in low-ionization regions distributed inhomogeneously throughout the nebula. The total abundances relative to hydrogen are determined to be 0.000015 for S, 0.000053 for Ne, and 0.000007 for Ar; these abundances are shown to be within the range of published average values for planetary nebulae.

Bregman, J. D.↗
NASA NTRS1999

An Abundance Analysis of Two Carbon-Rich Proto-Planetary Nebulae: IRAS Z02229+6208 And IRAS 07430+1115

In this paper, we present an LTE abundance analysis of two new proto-planetary nebulae, IRAS Z02229 + 6208 and IRAS 07430 + 1115, based on high-resolution (R approximately equal 55,000) optical echelle spectra. Results show that both stars are metal-poor ([Fe/H] = -0.5) and overabundant in C, N, and s-process elements. The average elemental abundances are [C/Fe] = +0.8, [N/Fe] = +1.2, and [s-process/Fe] = +1.4 for IRAS Z02229 + 6208, and [C/Fe] = +0.6, [N/Fe] = +0.4, and [s-process/Fe] = +1.6 for IRAS 07430+ 1115. These abundances suggest that the stars have experienced nucleo-synthesis on the asymptotic giant branch (AGB), and the resultant products of CNO, 3alpha, and s-process reactions were brought to the photosphere during shell flashes and deep mixing episodes during the AGB phase of their evolution. Of major significance is the measurement of a high Li abundance in both stars, log epsilon(Li) approximately equal 2.3 and 2.4 for IRAS Z02229 + 6208 and IRAS 07430 + 1115, respectively. This may be the result of hot bottom burning, below the deep convective zone. We also present an analysis of the circumstellar molecular (C2 and CN) and atomic (Na I and K I) absorption spectra of both stars. We derive rotational temperatures, column densities, and envelope expansion velocities using molecular C2 Phillips and CN Red system bands. The values derived for expansion velocities, 8-14 km/s, are typical of the values found for post-AGB stars. IRAS 07430+ 1115 is unusual in that it shows P Cygni-shaped C2 emission profiles in the spectra of the circumstellar envelope. A minimum distance for IRAS Z02229+6208, determined from interstellar Na I lines, suggests that it is evolved from an intermediate-mass star. Including these two stars, the number of post-AGB stars for which clear C, N, and s-process elemental overabundances are found rises to eight. IRAS Z02229 + 6208 is known to possess the 21 micron emission feature in its mid-infrared spectrum; these results support the idea that all 21 micron emission stars are carbon-rich post-AGB stars.

Reddy, Bacham E.↗
NASA NTRS2018

Distribution of Alkalis (Na, Cs, Rb) Between Silicate and Sulfide: Implications for Planetary Volatile Depletion

The abundances of volatile elements in the Earth's mantle are correlated with their temperatures of condensation. This depletion can be due to either incomplete condensation of the elements during the nebula condensation or evaporation processes during planetary growth. Elements that have affinities with metals (siderophile) and sulfides (chalcophile) are additionally depleted due to their segregation into the core. Therefore, study of lithophile elements could be useful to isolate processes of volatilization and their effect on the abundance of the elements in the Earth's mantle. However, the correlation of these lithophile elements including alkali elements, with their temperatures of condensation shows a significant scatter, which is difficult to reconcile with a depletion by vaporization or incomplete condensation alone.

Boujibar, A.↗
NASA NTRS2012

Near-Infrared Band Strengths of Molecules Diluted in N2 and H2O Ice Mixtures Relevant to Interstellar and Planetary Ices

The relative abundances of ices in astrophysical environments rely on accurate laboratory measurements of physical parameters, such as band strengths (or absorption intensities), determined for the molecules of interest in relevant mixtures. In an extension of our previous study on pure-ice samples, here we focus on the near-infrared absorption features of molecules in mixtures with the dominant components of interstellar and planetary ices, H2O and N2. We present experimentally measured near-infrared spectral information (peak positions, widths, and band strengths) for both H2O- and N2-dominated mixtures of CO (carbon monoxide), CO2 (carbon dioxide), CH4 (methane), and NH3 (ammonia). Band strengths were determined during sample deposition by correlating the growth of near-infrared features (10,000-4000 per centimeter, 1-2.5 micrometers) with better-known mid-infrared features (4000-400 per centimeter, 2.5-25 micrometers) at longer wavelengths.

Strengths↗
NASA NTRS1983

Laboratory studies at high resolution of the infrared absorption spectra of a number of gases found in planetary atmospheres

The infrared absorption spectra of a number of gases found in planetary atmospheres were studied at high resolution. Absorption line measurements which can be of value for the interpretation of planetary spectra in terms of molecular abundances and conditions in the planetary atmospheres were provided. The high resolution spectra have yielded measurements of individual vibration rotation line parameters including positions, strengths, pressure broadened widths and, where assignments were unknown, the temperature sensitivity of the strengths. Such information allows the determinations of the absorption of a given molecular gas under planetary conditions of temperature and pressure and at the same time it provides the data necessary if the spectra are to be understood in terms of basic molecular theory. Thus this work has included spectral analysis in the form of line assignments as well as fitting of the data to Hamiltonian models. Such fitting is very useful in that it helps to confirm and extend the assignments.

Hunt, R. H.↗
NASA NTRS1977

Computer simulations of planetary accretion dynamics - Sensitivity to initial conditions

A computer simulation program which generates mature planetary systems using only Newtonian physics and accretion with unit sticking efficiency is examined. The dependence of the simulation on a variety of radial and vertical density distribution laws, on the ratio of gas to dust in the solar nebula, on the total nebular mass, and on the orbital eccentricity of the accreting grains is explored. To approach physically realistic models, these parameters are altered according to various empirically- and theoretically-suggested criteria. The program is found to generate many recognizable planetary systems, including multiple-star systems with accompanying planets; single stars surrounded only by asteroids; and systems with large Jovian planets, planets similar to Pluto, or objects of asteroidal mass, as well as the usual terrestrial planets. Planetary spacing in the simulation obeys a relation of the Titius Bode variety; in general, the number of planets per system is inversely proportional to the orbital eccentricity. Some reservations about the simulation program are expressed; however, it does support the idea of abundant and diverse planetary systems throughout the galaxy.

Isaacman, R.↗
NASA NTRSDate not supplied

Application of Support Vector Regression to Derive Crater Depth/Diameter From Satellite Images

Through the study of impact crater shapes, one can draw important conclusions about the nature and evolution of planetary surfaces [e.g., 1-4].In particular, studying the depth (d) to diameter (D)ratio (d/D) of a population of impact craters, in combination with crater count statistics, can yield valuable insights regarding rates of erosion and burial[5]. Motivated by the great abundance of available planetary surface image data, the goal of this project is to develop an efficient way to estimate d/D from satellite images of impact craters for which stereo information is not available [6]. We set out to develop and train a machine learning algorithm to extract d/D from a dataset of synthetic impact crater images for which model d/D is known. The applications of machine learning to planetary science are numerous and diverse [7], including automatic planetary surface mapping [8] and the detection of impact craters [9]. Our algorithm makes use of Support Vector Regression (SVR), which is a type of Support Vector Machine (SVM) [10, 11].SVMs are a branch of supervised machine learning valued for their straightforward implementation and versatility in solving both classification and regression problems. In regression analysis, an SVR algorithm produces a hyperplane function to fit the training data points, as well as an ε-tube that surrounds the hyperplane. Tunable hyperparameters include the width of the ε-tube (ε) and the amount an algorithm is penalized for points which fall outside the ε-tube.

L R Chin↗
NASA NTRS1990

Emission line nebulae in the Magellanic clouds

H II regions, planetary nebulae, and supernova remnants in the large and small Magellanic clouds have been favored targets among all galactic and extragalactic emission nebulae for study with the IUE satellite due to their known distances and low line of sight extinction. Several of the major results arising from successful IUE (International Ultraviolet Explorer) observations of these three types of emission nebulae in the clouds are presented. Carbon abundances in the H II regions from UV emission lines with implications regarding the chemical evolution of the clouds and stellar origins of these elements are discussed. The UV spectral characteristics of several evolved and young SNRs in the clouds with comparisons made to similar objects in the Galaxy and other nearby galaxies are discussed. CNO abundance variations among planetary nebulae and characteristics of their central stars with emphasis on the new insights provided regarding PN formation and C-N nucleosynthesis during the various AGB dredge-up phases are discussed.

Dufour, Reginald J.↗
NASA NTRS1990

On planetary nebulae as sources of carbon dust: Infrared emission from planetary nebulae of the galactic halo

Planetary nebulae of the galactic disk are generally seen to emit a thermal continuum due to dust grains heated by stellar and nebular photons. This continuum typically peaks between 25 and 60 micron m, so that the total power emitted by the dust is sampled well by the broad-band measurements made by IRAS. Researchers examine here the characteristics of the infrared emission from the four planetary nebulae which are believed on the basis of their low overall metallicities to belong to the halo population. These nebulae are of particular interest because they are the most metal-poor ionized nebulae known in our Galaxy, and offer the opportunity to probe possible dependences of the dust properties on nebular composition. Researchers present fluxes extracted from co-addition of the IRAS data, as well as ground-based near infrared measurements. Each of the four halo objects, including the planetary nebula in the globular cluster M15, is detected in at least one infrared band. Researchers compare the estimated infrared excesses of these nebulae (IRE, the ratio of measured infrared power to the power available in the form of resonantly-trapped Lyman alpha photons) to those of disk planetary nebulae with similar densities but more normal abundances. Three of the halo planetaries have IRE values similar to those of the disk nebulae, despite the fact that their Fe- and Si-peak gas phase abundances are factors of 10 to 100 lower. However, these halo nebulae have normal or elevated C/H ratios, due to nuclear processing and mixing in their red giant progenitors. Unlike the other halo planetaries, DDDM1 is deficient in carbon as well as in the other light metals. This nebula has a substantially lower IRE than the other halo planetaries, and may be truly dust efficient. Researchers suggest that the deficiency is due to a lack of the raw material for producing carbon-based grains, and that the main bulk constituent of the dust in these planetary nebulae is carbon.

Dinerstein, Harriet L.↗
NASA NTRS1984

Research in particles and fields

Research activities in cosmic rays, gamma rays, and astrophysical plasmas are reviewed. Energetic particle and photon detector systems flown on spacecraft and balloons were used to carry out the investigations. Specific instruments mentioned are: the high energy isotope spectrometer telescope, the electron/isotope spectrometer, the heavy isotope spectrometer telescope, and magnetometers. Solar flares, planetary magnetospheres, element abundance, the isotopic composition of low energy cosmic rays, and heavy nuclei are among the topics receiving research attention.

Stone, E. C.↗
NASA NTRS1988

Formation of ureilites by impact-melting of cabonaceous chondritic material

Ureilites are modeled as impact-melt products of CV-chondrite-like material. This model is consistent with the brecciated nature and cumulate textures of ureilites, O-isotopic constraints (which indicate ureilite derivation from an isotopically heterogeneous body like the CV-chondrite parent), the high abundance of planetary-type noble gases, and the relatively high concentrations of siderophile and chalcophile elements (indicating incomplete separation of metal-sulfide from silicate). Each ureilite may have been derived from a separate cratering event.

Rubin, Alan E.↗
NASA NTRS1997

Laboratory Investigations of Volatile Trapping in Comets

This grant supports research on the formation of comets and their role in delivering volatiles to the early Earth. The volatile delivery system is of special importance because of the fundamental role played by these volatiles in the origin and early evolution of life. Our work during the period under review focussed on a test of the way in which amorphous ice forming at temperatures below 75 K traps noble gases, and the use of the resulting data to interpret noble gas abundances found in planetary atmospheres. We have found that these experiments support the idea that comets were indeed significant contributors of volatiles to the Earth's inventory. The results of our research to date are summarized in the accompanying paper "From the Interstellar Medium to Planetary Atmospheres via Comets". Other papers published on this subject or using the results of our analyses are listed in the bibliography. Copies of currently available reprints are attached as part of this report.

Owen, Tobias C.↗
NASA NTRS2004

Migration Processes and Volatiles Inventory to the Inner Planets

Comets and asteroids colliding with the terrestrial planets can deliver volatiles and organic or prebiotic compounds to the planets, thereby depositing on the planets the fundamental building-blocks for life. The inner planets contain heavier and cosmically less abundant elements in an iron-silicate matrix than the giant planets. This can be caused by the following three mechanisms: uneven fractionation and condensation in the accretionary disk; unequal degree of degassing of the composed matter; and heterogeneous accretion. Asteroid-size bodies consisting of the last low-temperature condensates (similar to most primitive chondritic meteorites, and enriched in hydrated silicates and trapped gases) are believed to have fallen onto the inner planets during the process of the giant planets formation. The relative contribution of either endogenous (i.e. outgassing) or exogenous (i.e. asteroid/comet collisions) sources is difficult to assess, although it is constrained by the pattern of noble gas abundances in the planetary atmospheres.

Marov, M. Y.↗
NASA NTRS2015

Are the Clast Lithologies Contained in Lunar Breccia 64435 Mixtures of Anorthositic Magmas

The anorthositic crust of the Moon is often used as the archtypical example of a primary planetary crust. The abundance and purity of anorthosite in the Apollo sample collection and remote sensing data are generally attributed to an early global magma ocean which produced widespread floating plagioclase cumulates (the ferroan anorthosites; FANs. Recent geochronology studies report evidence of young (less than 4.4 Ga) FAN ages, which suggest that either some may not be directly produced from the magma ocean or that the final solidification age of the magma ocean was younger than previous estimates. A greater diversity of anorthositic rocks have been identified among lunar meteorites as compared to returned lunar samples. Granted that these lithologies are often based on small clasts in lunar breccias and therefore may not represent their actual whole rock composition. Nevertheless, as suggested by the abundance of anorthositic clasts with Mg# [Mg/(Mg+Fe)] less than 0.80 and the difficulty of producing the extremely high plagioclase contents observed in Apollo samples and the remote sensing data, modification of the standard Lunar Magma Ocean (LMO) model may be in order. To ground truth mission science and to further test the LMO and other hypotheses for the formation of the lunar crust, additional coordinated petrology and geochronology studies of lunar anorthosites would be informative. Here we report new mineral chemistry and trace element geochemistry studies of thick sections of a composite of FAN-suite igneous clasts contained in the lunar breccia 64435 in order to assess the significance of this type of sample for petrogenetic studies of the Moon. This work follows recent isotopic studies of the lithologies in 64435 focusing on the same sample materials and expands on previous petrology studies who identified three lithologies in this sample and worked on thin sections.

Simon, J. I.↗