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NASA NTRS1977

Graphite grain surface reactions in interstellar and protostellar environments

Surface reactions on warm (at least 60 K) graphite grains between lattice C atoms and impinging H and O atoms within or in the vicinity of H II regions can provide a prolific source of H2CO and other interstellar molecules. It is proposed that similar reactions in the primitive solar nebula led to the formation of the organic molecules found in carbonaceous chondrites. From this and related evidence, it is argued that most of the solid material in the solar system may have originated as interstellar grains.

Barlow, M. J.↗

NASA NTRS1980

Mesospheric cloud formations

Formation of mesospheric clouds as a result of deposition of large amounts of H2O by the heavy lift launch vehicle (HLLV) of the solar power satellite system is discussed. The conditions which must be met in order to form and maintain clouds near the mesopause are described. The frequency and magnitude of H2O injections from the HLLV rocket exhaust are considered.

Forbes, J. M.↗

NASA NTRS1994

Resonantly driven nonlinear density waves in protostellar disks

Recent observations of binary, pre-main-sequence, solar-type stars provide evidence that such systems may coexist with circumstellar disks. The binary disk systems, besides being of general interest for the study of star formation, potentially provide useful tests of companion-disk interaction theories prominent in current hypotheses of planet formation. In this paper, we apply an asymptotic analysis of the nonlinear, resonant interaction of a stellar companion with a disk to understand the dependence of such interactions on the properties of the system: the binary mass ratio, the physical properties of the disk, and the effective dissipation (treated herein as viscosity). The method is based on a WKBJ approximation and exploits the conditions that the disk is thin and much less massive than the primary, but does not require that the companion-induced disturbance be small. Both isothermal and adiabatic responses are treated. Only circular orbit resonances are considered in this paper. It is demonstrated that the temperature of the disk as well as the relative mass of the companion affects the degree of nonlinearity, and that nonlinearity promotes high wave compression ratios, long wavelengths, and increased propagation distances. Nevertheless, the total torque exerted between the companion and the disk is well represented by linear theory. The amplitudes of density disturbances are reduced by viscosity and nonisothermality. Because resonant interactions are generally strong and capable of driving rapid evolution, one might expect observations of systems undergoing strong, resonant-driven evolution to be rare. In this connection, it is pointed out that the m = 1 resonance is distinguished by being anomalously weaker than the others and is therefore of observational interest. It is speculated that, in conditions of intrinsically small dissipation, the propagation of resonant-driven density waves is limited by the tendency of their wavelength to diminish with distance, and that the propagation distance (and therefore the region of the disk to which angular momentum is redistributed) is set by the distance at which the wavelength becomes comparable to the disk thickness.

Yuan, Chi↗

NASA NTRS2001

Substantial reservoirs of molecular hydrogen in the debris disks around young stars

Circumstellar accretion disks transfer matter from molecular clouds to young stars and to the sites of planet formation. The disks observed around pre-main-sequence stars have properties consistent with those expected for the pre-solar nebula from which our own Solar System formed 4.5 Gyr ago. But the 'debris' disks that encircle more than 15% of nearby main-sequence stars appear to have very small amounts of gas, based on observations of the tracer molecule carbon monoxide: these observations have yielded gas/dust ratios much less than 0.1, whereas the interstellar value is about 100 (ref. 9). Here we report observations of the lowest rotational transitions of molecular hydrogen (H2) that reveal large quantities of gas in the debris disks around the stars beta Pictoris, 49 Ceti and HD135344. The gas masses calculated from the data are several hundreds to a thousand times greater than those estimated from the CO observations, and yield gas/dust ratios of the same order as the interstellar value.

unmanned↗

NASA NTRS2008

Enhanced Reporting of Mars Exploration Rover Telemetry

Mars Exploration Rover Enhanced Telemetry Extraction and Reporting System (METERS) is software that generates a human-readable representation of the state of the mobility and arm-related systems of the Mars Exploration Rover (MER) vehicles on each Martian solar day (sol). Data are received from the MER spacecraft in multiple streams having various formats including text messages, sparsely-sampled engineering quantities, images, and individual motor-command histories.

Maimone, Mark W.↗

NASA NTRS2018

The Path Towards High-Contrast Imaging with the VLTI: The Hi-5 Project

The development of high-contrast capabilities has long been recognized as one of the top priorities for the VLTI (Very Large Telescope Interferometer). As of today, the VLTI routinely achieves contrasts of a few 103 in the near-infrared with PIONIER (Precision Integrated-Optics Near-infrared Imaging ExpeRiment) (H band) and GRAVITY (K band). Nulling interferometers in the northern hemisphere and non-redundant aperture masking experiments have, however, demonstrated that contrasts of at least a few 10 (sup -3) are within reach using specific beam combination and data acquisition techniques. In this paper, we explore the possibility to reach similar or higher contrasts on the VLTI. After reviewing the state-of-the-art in high-contrast infrared interferometry, we discuss key features that made the success of other high-contrast interferometric instruments (e.g., integrated optics, nulling, closure phase, and statistical data reduction) and address possible avenues to improve the contrast of the VLTI by at least one order of magnitude. In particular, we discuss the possibility to use integrated optics, proven in the near-infrared, in the thermal near-infrared (L and M bands, 3-5 microns), a sweet spot to image and characterize young extra-solar planetary systems. Finally, we address the science cases of a high-contrast VLTI imaging instrument and focus particularly on exoplanet science (young exoplanets, planet formation, and exozodiacal disks), stellar physics (fundamental parameters and multiplicity), and extragalactic astrophysics (active galactic nuclei and fundamental constants). Synergies and scientific preparation for other potential future instruments such as the Planet Formation Imager are also briefly discussed. This project is called Hi-5 for High-contrast Interferometry up to 5 microns.

PIONIER (H band)↗

NASA NTRS2008

The International Heliophysical Year

It is now widely recognized that evolution in the solar system proceeds through a set of Universal Processes, i.e. reconnection, particle acceleration, plasma wave generation and propagation, etc. By studying these Universal Processes together, in diverse environments, and in a comparative way, new scientific insights will be gained. This is perhaps best understood by citing a few examples: (I) Shocks are observed in situ in the interplanetary medium, shocks are believed to play a role in the acceleration of particles in the solar corona, and standing bow shocks and termination shocks separate the major regions in the heliosphere. Shock formation, and particle acceleration are universal processes. (2) Aurorae are observed on Earth, Saturn, and Jupiter, and Jovian auroral "footprints" have been observed on 10, Ganymede and Europa. The formation of aurorae is observed to be the universal response of a magnetized body in the solar wind. The International Heliophysical Year (IHY) specifically highlights the cross-disciplinary study of universal physical processes in the solar system, observed in a variety of settings. The study of these processes will provide new insights that will lead to a better understanding of the universal processes in the solar system that affect the interplanetary and planetary environments, and pave the way for safe human space travel to the Moon and planets in the future, and it will serve to inspire the next generation of space physicists.

Davila, Joseph M.↗

NASA NTRS1994

The detection and study of pre-planetary disks

A variety of evidence suggests that at least 50% of low-mass stars are surrounded by disks of the gas and dust similar to the nebula that surrounded the Sun before the formation of the planets. The properties of these disks may bear strongly on the way in which planetary systems form and evolve. As a result of major instrumental developments over the last decade, it is now possible to detect and study the circumstellar environments of the very young, solar-type stars in some detail, and to compare the results with theoretical models of the early solar system. For example, millimeter-wave aperture synthesis imaging provides a direct means of studying in detail the morphology, temperature and density distributions, velocity field and chemical constituents in the outer disks, while high resolution, near infrared spectroscopy probes the inner, warmer parts; the emergence of gaps in the disks, possibly reflecting the formation of planets, may be reflected in the variation of their dust continuum emission with wavelength. We review progress to date and discuss likely directions for future research.

Sargent, A. I.↗

NASA NTRS1978

Calcium isotopic anomalies in the Allende meteorite

Isotopic anomalies in Ca are reported which were found in two Ca-Al-rich inclusions of the Allende meteorite. The corrected Ca data show nonlinear isotopic effects in Ca-48 of +13.5 per mil and in Ca-42 of +1.7 per mil for one sample. The second sample shows a Ca-48 depletion of -2.9 per mil, but all other isotopes are normal. Samples with large excesses in Mg-26 show no Ca anomalies. The effects demonstrate that isotopic anomalies exist for higher-atomic-number refractory elements in solar-system materials and do not appear to be readily explainable by a simple model. Observed anomalous Mg and Ca compositions for coexisting mineral phases are uniform within each inclusion and require initial isotopic homogeneity within an inclusion but the preservation of wide variations between inclusions. Assuming formation of these inclusions by condensation from a gaseous part of the solar nebula, this implies isotopic heterogeneity on a scale of 10 to 100 km within the nebula.

Lee, T.↗

NASA NTRS1991

Scientific requirements for space science data systems

In the 1990's space plasma physics studies will increasingly involve correlative analysis of observations from multiple instruments and multiple spacecraft. The solar terrestrial physics missions in the 1990's will be designed around simultaneous observations from spacecraft monitoring the solar wind, the polar magnetosphere and the near and distant magnetotail. Within these regions, clusters of spacecraft flying in formation will increasingly involve comparative magnetospheric studies. No single lab will have the expertise to process and analyze all of the different types of data so the data repositories will be distributed. Catalog and browse systems will be required to help select events for study. Data compression techniques may be useful in designing the data bases used for selecting events for study. Data compression onboard the spacecraft will be necessary, since instrument data rates will be much larger than available telemetry rates. However, considerable care will be necessary to avoid losing valuable data when applying data compression algorithms.

Walker, Raymond J.↗

NASA NTRS1982

Dynamical constraints on the formation and evolution of planetary bodies

The present investigation is concerned with a number of inferences as to the origin of planetary bodies, taking into account the present dynamical state of the solar system and some of the limitations which apply to the considered conclusions. Attention is given to the dynamical processes, specifically those processes which may have influenced the orbital or rotational properties of the planets and satellites. Collisional processes are explored, taking into consideration orbital spacing, planetary rotation, and stochastic effects. In connection with a discussion of the evolution of rotational motion, spin state evolution is investigated along with spin axis precession and resonance variation, and the Cassini states. The evolution of planetary orbits is also studied. The subjects considered are related to tides, secular resonances, disk dynamics, and disk-satellite interactions.

Harris, A. W.↗

NASA NTRS1982

Evolution of Ca-Al-rich bodies in the earliest solar system Growth by incorporation

Thirty different Allende Ca-Al-rich inclusions (CAIs), 11 of type A and 19 of type B, were examined for spinel palisades and framboids, and the possible origins of these structures are discussed. Possible mechanisms for in situ formation of palisades are assessed, all of them either being rejected outright or considered highly implausible. The evidence for external formation and incorporation of palisade bodies is then assessed, and possible mechanisms are considered. It is proposed that type B CAIs are residues from the heating and incomplete evaporation of interstellar dust during the accretion of the protosolar nebula, and that type A CAIs are later condensates from completely evaporated dust whose exotic O-16-rich component became more diluted in the gas phase.

Wark, D. A.↗

NASA NTRS1973

Interstellar molecules - Formation in solar nebulae

Herbig's (1970) hypothesis that solar nebulae might be the principal source of interstellar grains and molecules is investigated. The investigation includes the determination of physical and chemical conditions in the early solar system. The production of organic compounds in the solar nebula is studied, and the compounds in meteorites are compared with those obtained in Miller-Urey and Fischer-Tropsch-type (FTT) reactions, taking into consideration aliphatic hydrocarbons, aromatic hydrocarbons, purines, pyrimidines, amino acids, porphyrins, and aspects of carbon-isotope fractionation. It is found that FTT reactions account reasonably well for all well-established features of organic matter in meteorites investigated. The distribution of compounds produced by FTT reactions is compared with the distribution of interstellar molecules. Biological implications of the results are considered.

Anders, E.↗

NASA NTRS2004

Collisional and Dynamical Evolution of Planetary Systems

Senior Scientst S. J. Weidenschilling presents his final administrative report in the research program entitled "Collisional and Dynamical Evolution of Planetary Systems," on which he was the Principal Investigator. This research program produced the following publications: 1) "Jumping Jupiters" in binary star systems. F. Marzari, S. J. Weidenschilling, M. Barbieri and V. Granata. Astrophys. J., in press, 2005; 2) Formation of the cores of the outer planets. To appear in "The Outer Planets" (R. Kallenbach, ED), ISSI Conference Proceedings (Space Sci. Rev.), in press, 2005; 3) Accretion dynamics and timescales: Relation to chondrites. S. J. Weidenschilling and J. Cuzzi. In Meteorites and the Early Solar System LI (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005; 4) Asteroidal heating and thermal stratification of the asteroid belt. A. Ghosh, S. J.Weidenschilling, H. Y. McSween, Jr. and A. Rubin. In Meteorites and the Early Solar System I1 (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005.

Weidenschilling, Stuart J.↗

NASA NTRS1982

Polycrystalline silicon availability for photovoltaic and semiconductor industries

Markets, applications, and production techniques for Siemens process-produced polycrystalline silicon are surveyed. It is noted that as of 1982 a total of six Si materials suppliers were servicing a worldwide total of over 1000 manufacturers of Si-based devices. Besides solar cells, the Si wafers are employed for thyristors, rectifiers, bipolar power transistors, and discrete components for control systems. An estimated 3890 metric tons of semiconductor-grade polycrystalline Si will be used in 1982, and 6200 metric tons by 1985. Although the amount is expected to nearly triple between 1982-89, research is being carried out on the formation of thin films and ribbons for solar cells, thereby eliminating the waste produced in slicing Czolchralski-grown crystals. The free-world Si production in 1982 is estimated to be 3050 metric tons. Various new technologies for the formation of polycrystalline Si at lower costs and with less waste are considered. New entries into the industrial Si formation field are projected to produce a 2000 metric ton excess by 1988.

Ferber, R. R.↗

NASA NTRS1981

Isotopic anomalies in the galactic cosmic-ray source

Observations of the isotopic compositions of oxygen, neon and magnesium nuclei in galactic cosmic rays are presented and discussed in terms of nucleosynthesis at the galactic cosmic ray source. The observations, made with a charged-particle telescope carried aboard ISEE-3, show enhancements in the Ne-22/Ne-20, Mg-25/Mg-24 and Mg-26/Mg-24 ratios with respect to solar system abundances by factors of 4.1, 1.6 and 1.6, respectively. The data thus demonstrate that the galactic cosmic ray source is compositionally distinct from the solar system, and also rule out the models of Woolsey and Weaver (in press) for the synthesis of excess Ne-22 and a model of normal star formation, evolution and mass loss in a region enriched in metals.

Wiedenbeck, M. E.↗

NASA NTRS1981

Infrared astronomical data base and catalog of infrared observations

The NASA/Goddard Space Flight Center has developed a computer data base of infrared astronomical observations. The data base represents a machine-readable library of infrared observational data published in the relevant literature since 1960 for celestial sources outside the solar system. It likewise includes the contents of infrared surveys and catalogs. A catalog of infrared observations has been developed in both printed and magnetic-tape formats. The data base will be accessed through a bibliographic guide and an atlas of infrared source names and positions. Future plans also include two-dimensional graphical displays of infrared data and a user-interactive data terminal.

Schmitz, M.↗

NASA NTRS1991

Oxygen isotope studies of ordinary chondrites

Several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components (chondrules, fragments, clasts, and matrix). The whole-rock isotopic compositions reflect the iron-group of the meteorite (H, L, or LL). Isotopic uniformity of H3 to H6 and L3 to L6 are consistent with closed-system metamorphism within each parent body. LL3 chondrites differ slightly from LL4 to LL6, implying a small degree of open-system aqueous alteration and carbon reduction. On the scale of individual chondrules, the meteorites are isotopically heterogeneous, allowing recognition of the solar-nebular processes of chondrule formation. Chondrules for all classes of ordinary chondrites are derived from a common population, which was separate from the population of chondrules in carbonaceous or enstatite chondrites. Chondrules define an isotopic mixing line dominated by exchange between (O - 16)-rich and (O - 16)-poor reservoirs. The oxygen isotopic compositions of chondrites serve as 'fingerprints' for identification of genetic association with other meteorite types (achondrites and iron) and for recognition of source materials in meteoritic breccias.

Clayton, Robert N.↗