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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Charged particle modification of ices in the Saturnian and Jovian systems

The modification by ion bombardment of the surfaces of icy objects in the Saturnian and Jovian systems is discussed. Chemical changes in ices are induced by breaking of bonds and by implantation of incident ions. Long-term irradiation by fast ions produces physical changes such as increasing the surface reflectivity and ability to scatter light. On large satellites, molecules which are ejected by ion bombardment are redistributed across the surfaces of large satellites. For small satellites and ring particles bombarded by ions, such as those of Saturn, most or all of the sputtered material is lost to space, forming a neutral torus in the locale of the satellite orbits and rings and supplying ions to the magnetosphere. Noting the existence of such a torus, the sputter erosion and possible stabilization of the E-ring of Saturn is discussed.

Johnson, R. E.↗
NASA NTRS1985

On bipolar ejection

Observations of bipolar outflows, including jets often with clumpy concentrations of matter, have been made for a wide variety of astronomical systems. In most but not all of the systems, an accretion disk is present. It is proposed that the general process responsible for bipolar ejection involves the conversion of rotational energy into magnetic energy, usually in the form of a polar magnetic torus, deep in the interiors of the systems involved. If the buoyancy of the torus resullts in draining the field lines of most of the matter which they thread, then the acceleration of the remaining matter in the toroidal bubble may produce velocities in excess of the escape velocity from the surface of the system. It is contemplated that this process will be repeated many times in most systems. A discussion is given of the application of these ideas to protostars, to stars evolved beyond the main sequence, to neutron stars, and to black holes on both stellar and galactic scales.

Cameron, A. G. W.↗
NASA NTRS1986

Modeling and investigative studies of Jovian low frequency emissions

The Voyager data in a newly produced noise-reduced and recalibrated format has been received. New color spectrograms were developed on high resolution color terminals which display this data. The production of these new spectrograms utilizing the new format data is quite important, because it eliminates a serious problem of noise contamination and miscalibration in the old data set. In addition, a new Jovian plasma model was introduced, which includes the Io torus and accounts for 7 ionic species. The new plasma model is important in the ray tracing of hectometric (HOM) and kilometric (KOM) radiation which may be influenced by the Io torus.

Menietti, J. D.↗
NASA NTRS1987

Magnetospheric plasma sputtering of Io's atmosphere

Neutral coronae due to magnetospheric ion sputtering from the exobase are generated, and ion and neutral injection into the plasma torus are calculated, on the assumption of the existence of an atmosphere on Io and a consideration of that atmosphere's various possible characteristics. Through the inclusion of the sputtered atmospheric corona that emerges from an assumed unattenuated incident ion flux, it becomes possible to satisfy the supply rate to the torus with an exobase that is close to the surface; such an exobase would imply that the Io atmosphere is insufficiently robust to support a fully dissociated corona, and that a significant fraction of the incident plasma ions can penetrate to the surface to furnish a sputter source of atmospheric gas.

Mcgrath, M. A.↗
NASA NTRS1987

Observations of the Jovian UV aurora by Voyager

The observations of the Jovian aurora made by the Voyager UV spectrometer (UVS) during 1979 are analyzed, with special consideration given to the model fitting process. Several different estimates of the function specifying auroral arc geometry were tried, with the Broadfoot et al. (1981) estimate, found by probing with the tip of the UVS slit, giving the best agreement; this agreement is slightly better than the agreement with the Io torus footprint computed by Roederer et al. (1977). The results suggest that the UVS observations are more sensitive to the surface field geometry than are the Voyager flyby in situ observations. The results of a study of intensity maximum positions indicate that the particles exciting the spatially variable portion of the aurora are drifting west, implying either that these particles are electrons or that they are positive ions drifting east more slowly than the corotation lag of the Io torus region carries them to the west. The latter case is most consistent with the high-energy charged particle measurements.

Herbert, Floyd↗
NASA NTRS1988

A modeling analysis program for the JPL table mountain Io sodium cloud data

Research in the third and final year of this project is divided into three main areas: (1) completion of data processing and calibration for 34 of the 1981 Region B/C images, selected from the massive JPL sodium cloud data set; (2) identification and examination of the basic features and observed changes in the morphological characteristics of the sodium cloud images; and (3) successful physical interpretation of these basic features and observed changes using the highly developed numerical sodium cloud model at AER. The modeling analysis has led to a number of definite conclusions regarding the local structure of Io's atmosphere, the gas escape mechanism at Io, and the presence of an east-west electric field and a System III longitudinal asymmetry in the plasma torus. Large scale stability, as well as some smaller scale time variability for both the sodium cloud and the structure of the plasma torus over a several year time period are also discussed.

Smyth, William H.↗
NASA NTRS1987

Correlating east-west asymmetries in the Jovian magnetosphere and the Io sodium cloud

Three east-west intensity asymmetries in the Jupiter system that would appear to an earth observer in optical S+, extreme ultraviolet S++ and optical Na emissions are reviewed. The three asymmetries imply that some combination of the plasma torus number densities and electron temperature is, on the long-term average, larger west of Jupiter than east of Jupiter. A small east-to-west electric field, previously proposed to explain the ion intensity asymmetries, is also shown to provide a natural explanation for the sodium intensity asymmetry. A long-term average east-to-west electric field of about 3 mV/m and a corresponding west-to-east offset of about 0.16 Jupiter radii for the plasma torus at Io's orbital distance are implied. On a shorter time scale, the east-west electric field appears to be time variable and may be readily monitored from earth by observations of the sodium cloud.

Smyth, William H.↗
NASA NTRS1987

Limits on the extent of Saturn's hydrogen cloud

The 30-day reports from the Voyager Ultraviolet Spectrometer team characterize the atomic hydrogen observed near Saturn as a torus with a half width of 7 Saturnian radii. The atomic processes occurring in the inner magnetosphere are modelled, including sputtering, ionization, charge exchange, ion-atom interchange, recombination, and transport, and a neutral hydrogen source is added to test the proposal that a hydrogen cloud exists in this region. Plasma observations in the inner magnetosphere are found to be inconsistent with the presence of a dense atomic hydrogen cloud. Thus, it is concluded that the hydrogen cloud must be a torus as originally reported, and that the cloud does not extend inward to the orbits of the inner satellites of Saturn.

Richardson, John D.↗
NASA NTRS1987

Neutron tori and the origin of r-process elements

It is shown here that if an accretion disk gets hotter than a few MeV, nuclei in the infalling matter are dissociated into their constituent neutrons and protons. Neutrons released by dissociation of matter falling at high accretion rates into a black hole or neutron star accumulate in a dense 'neutron torus'. The occurrence of the classical rapid or r-process nucleosynthesis in such a torus is investigated.

Hogan, C. J.↗
NASA NTRS1988

A general model for Io's neutral gas clouds. II - Application to the sodium cloud

A previously developed neutral cloud model is applied to the neutral sodium cloud produced by Io. Past models for the cloud are reviewed and the motivation for developing better models is discussed. The interactions of sodium in the plasma torus are discussed. It is shown how the new model can be used to provide a consistent physical explanation for the basic physical characteristics of the spatially extended Io sodium cloud and for the east-west intensity asymmetry observed very near Io. This leads to definite conclusions regarding the flux distribution and density of sodium in Io's exosphere, the level of the collisional exobase in the atmosphere, the nature of the interaction of the corotating plasma torus and the satellite atmosphere/corona, and the presence of an east-west electric field in the planetary system.

Smyth, W. H.↗
NASA NTRS1988

Iterates of maps with symmetry

Fixed-point bifurcation, period doubling, and Hopf bifurcation (HB) for iterates of equivariant mappings are investigated analytically, with a focus on HB in the presence of symmetry. An algebraic formulation for the hypotheses of the theorem of Ruelle (1973) is derived, and the case of standing waves in a system of ordinary differential equations with O(2) symmetry is considered in detail. In this case, it is shown that HB can lead directly to motion on an invariant 3-torus, with an unexpected third frequency due to drift of standing waves along the torus.

Chossat, Pascal↗
NASA NTRS1989

Source location of Jupiter's decametric radiation and UV aurora

The source region of a component of Jovian Io-unrelated decametric radiation is inferred geometrically based on simultaneous observations from Voyager spacecraft and a ground-based observatory with the aid of a hollow cone beam model and model of the Jovian magnetic field. The results indicate that the sources of this component lie above the northern hemisphere, and on field lines that connect the Io plasma torus and the Jovian ionosphere in the so-called active sector. It is concluded that an interaction between the Io-torus plasma and the ionospheric plasma through a thin flux tube initiates the decametric radiation.

Maeda, Koitiro↗
NASA NTRS1989

Plasma pressure in the environment of Jupiter, inferred from Voyager 1 magnetometer observations

A model combining the internal magnetic field with a self-consistent model of the Jovian magnetodisc was fitted to the Voyager 1 Jovian magnetic field data by means of a generalized inverse technique. The model parameters included the internal field spherical harmonic coefficients as well as with parameters describing the plasma distribution in the magnetosphere. Assuming that the pressure in the middle and outer magnetosphere is related to the unit flux tube volume V through PV exp gamma = const, the model fit yielded a value of 0.88 for gamma. If the hot (30 keV) plasma is transported adiabatically inward under the interchange instability triggered by centrifugal force of the heavy torus ions, losses are not sufficient to account for such a low value of gamma beyond L = 10. Closer to the planet, as the outer edge of the Io plasma torus is approached, PV exp gamma is found to decrease inward, as expected from the particle measurements, which identified an inner boundary of the particle fluxes in that region. With the present stage of the development of magnetodisc models, secular variations of the internal field still remain difficult to estimate.

Caudal, G.↗
NASA NTRS1990

Zodiacal dust bands - Their relation to asteroid families

The zodiacal dust band phenomenon is presently reproduced by a mathematical model of orbitally evolved collisional debris spatial distributions whose torus exhibits particle-density maxima at heliocentric latitudes near its constituent particles' mean proper orbital inclinations, as well as near the loci of the particle orbits' perihelia and aphelia. Models of dust toruses for seven asteroid families are generated and compared with observations of the principal dust bands. Nonequilibrium models of dust band production and evolution furnish a framework within which all dust band observations can be understood.

Sykes, Mark V.↗
NASA NTRS1990

The NASA-Lewis program on fusion energy for space power and propulsion, 1958-1978

An historical synopsis is provided of the NASA-Lewis research program on fusion energy for space power and propulsion systems. It was initiated to explore the potential applications of fusion energy to space power and propulsion systems. Some fusion related accomplishments and program areas covered include: basic research on the Electric Field Bumpy Torus (EFBT) magnetoelectric fusion containment concept, including identification of its radial transport mechanism and confinement time scaling; operation of the Pilot Rig mirror machine, the first superconducting magnet facility to be used in plasma physics or fusion research; operation of the Superconducting Bumpy Torus magnet facility, first used to generate a toroidal magnetic field; steady state production of neutrons from DD reactions; studies of the direct conversion of plasma enthalpy to thrust by a direct fusion rocket via propellant addition and magnetic nozzles; power and propulsion system studies, including D(3)He power balance, neutron shielding, and refrigeration requirements; and development of large volume, high field superconducting and cryogenic magnet technology.

Schulze, Norman R.↗
NASA NTRS1991

Protostellar condensations in the core of NGC 2024

The J = 4-3 transition of HCO(+) was observed in the core of NGC 2024. The findings indicate a possibly expanding torus centered around the FIR 6 continuum source and an E-W ridge below the ionization front. The presence of HCO(+) J = 4-3 emission from the torus and E-W ridge suggests relatively high gas densities in these regions. The relatively strong intensity of the observed HCO(+) J = 4-3 emission toward the FIR source suggests that the emission originates from relatively warm and dense gas. Continuum radiation transport modeling of the core shows that submillimeter and millimeter continuum observations of the cores can be reproduced under the assumption that the cores are externally heated objects without internal heating sources. This requires a factor of about 250 enhancement of the external radiation field intensity compared to the standard Galactic radiation field. This enhancement is consistent with the stellar luminosities required to explain the observed FIR continuum emission from the region.

Lis, D. C.↗
NASA NTRS1991

Molecular origin of Io's fast sodium

Neutral sodium emissions encircling Jupiter exhibit an intricate and variable structure that is well matched by a simple loss process from Io's atmosphere. These observations imply that fast neutral sodium is created locally in the Io plasma torus, both near Io and as much as 8 hours downstream. Sodium-bearing molecules may be present in Io's upper atmosphere, where thay are ionized by the plasma torus and swept downstream. The molecular ions dissociate and dissociatively recombine on a short time scale, releasing neutral fragments into escape trajectories from Jupiter. This theory explains a diverse set of sodium observations, and it implies that molecular reactions (particularly electron impact ionization and dissociation) are important at the top of Io's atmosphere.

Schneider, Nicholas M.↗
NASA NTRS1991

Voyager 2 electron observations in the magnetosphere of Neptune

This paper describes electron data obtained during the Neptune encounter by the Voyager 2 plasma science experiment. The densities and temperatures of low-energy (10-5950 eV) electrons and the electrostatic potential of the spacecraft near Neptune are derived. The data indicate that the escape of charged particles from Triton and the local ionization of atoms in the neutral torus originating from Triton are the major plasma sources. It is inferred that this neutral torus of hydrogen atoms has a density of about 300/cu cm and an inner boundary at 8 R(N). The data near Neptune exhibit signatures suggesting that both precipitation into Neptune's atmosphere and ring absorption are important plasma loss mechanisms. Plasma transport in the magnetosphere appears to be very fast; the diffusion coefficient is 1 x 10 exp -7 L exp 3 R(N) exp 2/sec.

Zhang, Ming↗