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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
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↗
NASA NTRS1992

The abundance of O(2+) in the Jovian magnetosphere

From a synthesis of data from the Plasma-Science and Ultraviolet-Science instruments on Voyager 1 a radial profile is presented of O(2+) abundance between 4.9 and 42 Jovian radii. A sharp rise is noted in O(2+) mixing ratio near 7.5 Jovian radii, coincident with a sharp rise in effective electron temperature at the outer boundary of the Io plasma torus. Beyond 8.5 Jovian radii the O(2+) mixing ratio is found to be roughly constant which indicates freezing of the ionization prevailing at the outer edge of the hot torus.

Bagenal, F.↗
NASA NTRS1992

Plasma heating of Io's atmosphere

A Monte-Carlo, molecule-tracking program was constructed to describe the structure of Io's atmosphere in the region penetrated by ions from the plasma torus. This region is shown to exhibit high temperatures, consistent with corona observations, independent of whether significant UV heating also occurs. The atmospheric structure is determined near the exobase, which is the region responsible for the supply of the Io torus.

Pospieszalska, M. K.↗
NASA NTRS1992

Defining the background status of a debris cloud

When a satellite fragments, a debris cloud is produced which continues to orbit the earth in its place. The fragments do not remain in the same orbit as their parent, however, and the shape of this cloud begins to evolve. Over the course of several years, the cloud changes from an ellipsoid, to a pinched torus in the parent orbital plane, to a full torus in the equatorial plane, after which time it is considered to be part of the background environment. The elapsed time between breakup and background is called the time-to-background (TTB) and is calculated differently by different researchers. This report reviews existing methods employed by programs DEBRIS and SCREEN for determining the TTB, and offers two others for consideration for a community-wide standard. It is concluded that while each method has its merits, the debris community should agree on a specific computational definition for TTB that could be used as an industry-wide standard for comparing results.

Maclay, Timothy D.↗
NASA NTRS1992

Galileo Ultraviolet Spectrometer experiment

The Galileo ultraviolet spectrometer experiment uses data obtained by the Ultraviolet Spectrometer (UVS) mounted on the pointed orbiter scan platform and from the Extreme Ultraviolet Spectrometer (EUVS) mounted on the spinning part of the orbiter with the field of view perpendicular to the spin axis. The UVS is a Ebert-Fastie design that covers the range 113-432 nm with a wavelength resolution of 0.7 nm below 190 and 1.3 nm at longer wavelengths. The UVS spatial resolution is 0.4 deg x 0.1 deg for illuminated disk observations and 1 deg x 0.1 deg for limb geometries. The EUVS is a Voyager design objective grating spectrometer, modified to cover the wavelength range from 54 to 128 nm with wavelength resolution 3.5 nm for extended sources and 1.5 nm for point sources and spatial resolution of 0.87 deg x 0.17 deg. The EUVS instrument will follow up on the many Voyager UVS discoveries, particularly the sulfur and oxygen ion emissions in the Io torus and molecular and atomic hydrogen auroral and airglow emissions from Jupiter. The UVS will obtain spectra of emission, absorption, and scattering features in the unexplored, by spacecraft, 170-432 nm wavelength region. The UVS and EUVS instruments will provide a powerful instrument complement to investigate volatile escape and surface composition of the Galilean satellites, the Io plasma torus, micro- and macro-properties of the Jupiter clouds, and the composition structure and evolution of the Jupiter upper atmosphere.

Hord, C. W.↗