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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Voyager 2 photopolarimeter observations of Titan

Observations of Titan's whole-disk polarization at 2460 and 7500 A are presented and analyzed in terms of model scattering atmospheres. If the Titan aerosols are spherical or nearly spherical, no single combination of refractive index and size distribution is able to fit data at both wavelengths. However, a vertically inhomogeneous distribution suggested by Tomasko and Smith (1980), characterized by a size gradient with altitude, fits the data at 2640 A moderately well but must be modified at intermediate and large optical depths to fit the 7500-A data. Results for synthetic phase functions indicate that the single-scattering polarization must be 70 percent or larger in the UV and 78 percent or larger in the near-IR at 90-deg phase angle, depending on the phase function. If the correct phase function is similar to that for 0.5-micron-radius spheres, the UV single-scattered polarization must be 84 percent and the near-IR single-scattered polarization must be over 90 percent. Such large polarizations are impossible for 0.5-micron-radius spheres but may be possible for nonspherical particles with effective radii near 0.5 micron, although the existence of nonspherical particles with the scattering properties required by these and other observations has not been demonstrated.

West, R. A.↗
NASA NTRS1991

On the lack of a magnetic signature of Triton's magnetospheric interaction on the Voyager 2 flyby trajectory

There is strong, albeit indirect, evidence for a sub-Alfvenic and transonic interaction between Triton and the Neptunian magnetosphere. A new inspection of magnetic field data around Triton encounter shows no evidence for the interaction. It is shown that this is due to the geometry of Triton's Alfvenic wings, which were probably too far from the spacecraft during the encounter. The situation is complicated by finite ion gyroradius effects, which tend to smear out the simple Alfven wings such as encountered at Io.

Neubauer, F. M.↗
NASA NTRS1992

Cloud motions on Neptune from Voyager 2 images

The puzzle presented by Neptune's circulation is evidenced by its wide spectrum of wind speeds and differences between the drift rate of its longest lived features and its finer scale cloud forms, unlike Jupiter or Saturn. Neptune's clouds appear dynamic and show strong evidence of atmospheric waves, making cloud motion measurements somewhat difficult and requiring some departures from the methods which have been traditionally used to determine atmospheric circulations. New measurements of cloud motions of Neptune that confirm the general characteristics reported by Smith et al. (1989) are presented below. Besides greater number of measurements from a higher time resolution data set, the new results reveal the shape of the westerly jet at 72 deg S latitude.

Limaye, S. S.↗
NASA NTRS1980

The effect of coronal transport of energetic solar particles

A single active center was the origin of several solar flares observed in September, 1977. The longitude of the flares ranged from approximately 115 deg E to approximately 117 deg W. During this period Helios 1, Helios 2, Voyager 1 and Voyager 2 were extended over a range of approximately 120 deg in longitude, thus providing an opportunity to study the coronal transport of energetic solar flare particles. The result of a detailed study of the relative intensity and spectral shape of approximately 2-200 MeV protons and alphas at several solar longitudes has enabled the imposition of some criteria on models of coronal transport.

Conlon, T. F.↗
NASA NTRS2008

Magnetic Fields in the Termination Shock, Heliosheath and Solar Wind

This paper will discuss recent magnetic field observations of the termination shock (TS), heliosheath (HSH), and supersonic solar wind (SW) made by Voyager 1 (V1) and Voyager 2 (V2). Voyager 2 crossed the TS at least 5 times at 83.7 AU and 27.5deg South heliographic latitude during 2007/242.14 to 244.80. The structure of the shock, observed on three of the crossings, was highly variable, ranging from a simple quasi-perpendicular supercritical shock to a complex profile suggesting reformation. Two merged interaction regions were observed in the SW upstream of the TS, and the magnetic field increased to relatively high values during the month prior to crossing the TS. Voyager 2 observations in the HSH will also be discussed. Voyager 1 observed a small radial gradient of the magnetic field strength B in the HSH. It is expected that B should increase from the TS to heliopause, but the available predictions of the profile are not adequate to compare with the observations. Voyager 1 has entered a unipolar region, as the heliospheric current sheet moved below the latitude of V1.

Burlaga, L. F.↗
NASA NTRS1981

Interaction of eddies and mean zonal flow on Jupiter as inferred from Voyager 1 and 2 images

Voyagers 1 and 2 narrow angle frames are used to obtain displacements of features at resolutions of 130 km over time intervals of 1 Jovian rotation. It is shown that the mean zonal velocity profile does not change by a measurable amount between Voyagers 1 and 2, which is consistent with previous observations. It is also shown that the curvature of the velocity profile vanes varies with latitudes in the range from -3 beta to +2 beta. The barotropic stability criterion is violated at 10 latitudes between + and - 60 deg, and the rate of conversion of eddy kinetic energy into zonal mean kinetic energy is in the range from 1.5 to 3.0 per sq Wm for a layer 2.5 bar deep. The rate of energy conversion is more than 10% of the total infrared heat flux for Jupiter, as compared to the earth where it is only 0.1% of the infrared, which suggests that the two planets possess fundamentally different thermomechanical energy cycles.

Ingersoll, A. P.↗
DOE OSTI2021

A Foreshock Model for Interstellar Shocks of Solar Origin: Voyager 1 and 2 Observations

The Voyager 1 (V1) and Voyager 2 (V2) spacecraft were launched in 1977 on a mission to explore the outer planets and reach the heliopause, the boundary between the hot solar plasma and the relatively cool interstellar plasma. V1 reached the heliopause on 2012 August 25, at 121.6 au, and V2 reached the heliopause on 2018 November 5, at 119.0 au. One of their remarkable discoveries was the detection of shocks propagating into the interstellar plasma from energetic solar events. These shocks are typically preceded by electron plasma oscillations excited by electron beams streaming along interstellar magnetic field lines ahead of the shocks. The frequencies of the plasma oscillations have now provided radial electron density profiles in the outer heliosphere and in the interstellar medium to radial distances of more than 145 au. The oscillations are typically preceded by bursts of high-energy ∼5–100 MeV electrons. These electron bursts are interpreted as being due to the reflection (and acceleration) of cosmic-ray electrons by the shock at the time the shock first contacts the magnetic field line that passes through the spacecraft. Relative timing between the cosmic rays reflected by the shock and the onset of the plasma oscillations allow us, for the first time, to estimate the energy, ∼20–100 eV, of the electron beams responsible for the plasma oscillations. These observations are combined into a self-consistent model called the foreshock model that describes the interaction of shocks of solar origin with the interstellar plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1983

The September 1979 solar cosmic ray event

Observations of a long-lived solar particle event in September 1979, are presented. The energy flux observations were carried out simultaneously by the Voyager 2, ISEE-3, and IMP-8 satellites at widely separated radial positions. It is shown that the flux spectra of the particle population which arrived early at Voyager 2 extended to several MeV for each nucleon, although at energies above 1.5 MeV/nuc, the peak flux occurred one day later. The solar wind speed at Voyager 2 increased from about 600 km/s to 1000 km/s upon the arrival of the particles, causing rapid changes in the Voyager 2 connection longitude. It is suggested that the steepening observed in the maximum flux energy spectra above about 10 MeV/nuc at Voyager 2 may have been due to the injection of particles one day earlier.

Hamilton, D. C.↗
NASA NTRS1984

K-coronameter observations and potential field model comparison in 1976 and 1977

Results of determining the shape and location of the heliospheric current sheet from a potential field model and from K-coronameter observations are compared. Interplanetary magnetic field polarities as observed by IMP 8, Helios 1 and 2, and Voyager 2 spacecraft were used to test the two methods over the period May 1976 to August 1977 throughout 18 Carrington rotations. The computed heliospheric current sheets from both methods had a quasi-stationary four-sector structure and very similar shapes. Agreement between interplanetary magnetic field polarity and the results from the potential field model was found on 79 percent of the days, while agreement between the interplanetary field polarity and the polarities derived from the K-coronameter data was found on 87 percent of the days.

Bruno, R.↗
NASA NTRS1987

Simulation of January 1-7, 1978 events

The solar wind disturbances of January 1 to 7, 1978 are reconstructed by a modeling method. First, the interplanetary magnetic field (IMF) background pattern, including a corotating shock, is reproduced using the Stanford source surface map. Then, two solar flares with their onset times on January 1, 0717 UT at S17 deg E10 deg and 2147 UT S17 deg E32 deg, respectively, are selected to generate two interplanetary transient shocks. It is shown that these two shocks interacted with the corotating shock, resulting in a series of interplanetary events observed by four spacecraft, Helios 1 and 2, IMP-8 (Interplanetary Monitoring Platform 8), and Voyager 2. Results show that these three shock waves interact and coalesce in interplanetary space such that Helios 2 and Voyager 2 observed only one shock and Helios 1 and IMP-8 observed two shocks. All shocks observed by the four spacecraft, except the corotating shock at Helios 1, are either a transient shock or a shock which is formed from coalescing of the transient shocks with the corotating shock. The method is useful in reconstructing a very complicated chain of interplanetary events observed by a number of spacecraft.

Chao, J. K.↗