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Chenette, D. L.

Publications and source records attributed to Chenette, D. L..

31 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Energetic charged particles in Saturn's magnetosphere - Voyager 1 results

Voyager 1 provided the first look at Saturn's magnetotail and magnetosphere during relatively quiet interplanetary conditions. This report discusses the energetic particle populations of the outer magnetosphere of Saturn and absorption features associated with Titan and Rhea, and compares these observations with Pioneer 11 data of a year earlier. The trapped proton fluxes had soft spectra, represented by power laws in kinetic energy with an exponent of 7 in the outer magnetosphere and 9 in the magnetotail. Structure associated with the magnetotail was observed as close as 10 Saturn radii on the outbound trajectory. The proton and electron fluxes in the outer magnetosphere and in the magnetotail were variable and appeared to respond to changes in interplanetary conditions. Protons with energies greater than or approximately equal to 2 MeV had free access to the magnetosphere from interplanetary space and were not stably trapped outside about 7.5 Saturn radii.

Vogt, R. E.↗
NASA NTRS1980

The trapped radiations of Saturn and their absorption by satellites and rings

The Pioneer 11 encounter with Saturn has revealed the existence of a fully developed magnetosphere with high-energy trapped radiation about Saturn. The present paper gives a detailed summary of the energetic charged particle measurements, including the overall characteristics of the trapped electron, proton, and helium radiation, which was found to lie inside 20 Saturn radii from the planet, and the regions extending outward to beyond the planetary bow shocks and into the interplanetary medium.

Simpson, J. A.↗
NASA NTRS1980

Charged particle anisotropics in Saturn's magnetosphere

The paper deals with observations of anisotropies and pitch angle distributions for 0.5 to 1.8 MeV protons and 7 to 17 MeV electrons in Saturn's magnetosphere. In the outer magnetosphere (L = 6), there is clear evidence for corotation of the proton flux. The pitch-angle distribution shows maximum flux perpendicular to the magnetic field ('pancake' distribution). Observed changes in the amplitude and shape of the pitch angle distributions suggest the existence of substantial temporal variations in the outer magnetosphere. From L = 6 to L = 4, the proton intensity decreased by more than two orders of magnitude, while the pitch angle distribution shifted to a 'dumbbell' form (maximum flux parallel to magnetic field).

Bastian, T. S.↗
NASA NTRS1980

High-energy trapped radiation penetrating the rings of Saturn

Electrons and protons of energies from 2 to 25 MeV and greater than 67 MeV, respectively, have been discovered throughout the entire equatorial region inward from the outer edge of the A ring at L = 2.3 to the periapsis of the Pioneer trajectory at L = 1.3. The trapped radiation found in Saturn's magnetosphere beyond L = 2.3 is totally absent here. The present paper deals with the measurements in this region under the rings, and their interpretation.

Chenette, D. L.↗
NASA NTRS1980

The propagation of Jovian electrons to earth

An analysis of the Jovian electron flux increases observed by the earth-orbiting satellite Imp 8 throughout five 13 month Jovian synodic years during the period from launch of the satellite in 1973 to 1979 is presented. The analysis defines the characteristics of Jovian propagation to earth. Corotating interaction regions (CIR) that form at the leading edges of fast solar wind streams continue to modulate the propagation of MeV electrons from Jupiter to the orbit of the earth to produce approximately 27 day recurrent variations in the Jovian electron density. The new and significant result of this study is that these time-intensity profiles are more accurately described not by assumption that Jupiter is a constant source of electrons, but rather by assuming that electron emission is initiated with each passage of CIR by Jupiter with the emission continuing for only several days.

Chenette, D. L.↗
NASA NTRS1980

Saturnian trapped radiation and its absorption by satellites and rings - The first results from Pioneer 11

Preliminary results from Pioneer 11 concerning the acceleration and trapping of charged particles in the magnetic field of Saturn are reported. The identification and measurement of the intensities and spectra of charged particle species was performed by an experiment including four charged particle sensor systems, within 20 Saturn radii of the planet. Increases in the intensity of 0.5- to 1.8-MeV protons within 15 Saturn radii indicate the trapping and acceleration of particles in the dipole field region, while a decrease in proton intensity between seven and four Saturn radii is attributed to absorption by Dione and Enceladus and possibly ring material as well. Proton and electron intensity distributions are found to be axially symmetric within four Saturn radii, indicating a centered dipole aligned with the planetary rotation axis. Trapped radiation absorption at the orbit of Mimas is analyzed to obtain an upper limit of 4 x 10 to the -8th Saturn radii-squared/sec to the inward diffusion coefficient; an absorption-like feature observed at L = 2.5 is attributed to a previously unidentified satellite of diameter less than 200 km and semimajor axis 2.51 Saturn radii. Radiation absorption by the newly discovered F ring was also observed, however beneath the A, B and C rings a low flux of high-energy electrons was detected.

Simpson, J. A.↗
NASA NTRS1978

Jupiter's magnetosphere as a 'point source' for electrons propagating from 1 to 12 AU

A profile of electron intensities in the interplanetary medium from 1 to 12 AU obtained from Pioneer 10 measurements of the 3-6 MeV Jovian electron flux shows recurring intensity peaks, the amplitude of which decreases with increasing distance from Jupiter both in the direction of the sun and away from it. Concurrent IMP-8 measurements of the 2-12 MeV electron flux revealed a series of 27-day recurrent intensity increases modulated with a period of about 13 months, beginning about four months before the probable magnetic field connection between earth and Jupiter. Amplitudes of the intensity increases reached a maximum near the time of best connection. These results are consistent with a three-dimensional interplanetary diffusion model with Jupiter as a continuously emitting point source.

Chenette, D. L.↗
NASA NTRS1977

Observations of Jovian electrons at 1 AU throughout the 13 month Jovian synodic year

A study of Jovian electron-flux increases observed aboard the IMP-8 earth-orbiting satellite reveals that, contrary to previous reports of a 4-8-month Jovian electron 'season', Jovian electron-intensity increases were observed almost continuously from late 1973 into 1976, with peak intensities occurring at times of best connection between earth and Jupiter along the average direction of the interplanetary magnetic field about every 13 months. These observations are consistent with Jovian electron propagation both along and across the direction of the average interplanetary magnetic field. A convection-diffusion model for Jovian electron propagation, which assumes that Jupiter is a continuously emitting point source of electrons, originally developed to explain the distribution of Jovian electrons observed on the Pioneer 10 and 11 spacecraft, can account also for the distribution of Jovian electrons observed at the orbit of earth.

Chenette, D. L.↗
NASA NTRS1977

Acceleration of nucleons in interplanetary space and modulation of Jovian electrons at distances of 1 to 10 AU by corotating regions of solar origin

Corotating interaction regions (CIRs) are formed in interplanetary space when a fast solar-plasma flow overtakes a slow solar-wind stream. This paper shows that CIRs are closely related to two unusual phenomena observed during the flights of Pioneers 10 and 11. These include corotating periodic nucleon fluxes with energies of several MeV and variations in the intensity of relativistic Jovian electrons. Observational evidence is presented in favor of the idea that the nucleons are accelerated in CIRs located in interplanetary space at heliocentric distances of 1 to at least 10 AU, and a model is analyzed in which the acceleration takes place at the leading edge of a CIR. Pioneer data are cited which demonstrate that modulation by recurrent CIRs can explain the large-scale variations in Jovian electron intensity observed in interplanetary space.

Barnes, C. W.↗
NASA NTRS1976

Jovian electron bursts - Correlation with the interplanetary field direction and hydromagnetic waves

The bursts of relativistic electrons detected on Pioneer 10 upstream from Jupiter and within 400 Jovian radii of the planet have been found to be correlated with the interplanetary magnetic field. In three examples, electrons with energies between 3 and 6 MeV escaping from Jupiter's magnetosphere were observed only when the interplanetary magnetic field was along the Jupiter-spacecraft line. Large-amplitude interplanetary waves with characteristic periods of 10 min were found to be well correlated with intervals during which the field was along the Jupiter-spacecraft line. Abrupt changes in the field away from the preferred direction caused equally abrupt terminations of the waves with an accompanying reduction in the electron flux. These results are consistent with propagation of the electrons from Jupiter to Pioneer along the magnetic field lines. Hydromagnetic wave generation by Jovian charged particles, presumably the relativistic electrons themselves, as they travel upstream, appears to be an attractive explanation for the origin of the waves. At the observed frequency, hydromagnetic waves are Doppler-shifted to the gyrofrequency of the relativistic electrons. A plasma instability that appears capable of explaining the observations is a cyclotron overstability that occurs when the velocity of runaway electrons exceeds the velocity of hydromagnetic waves.

Smith, E. J.↗
NASA NTRS1975

Observations in interplanetary space of relativistic electrons from Jupiter

Evidence for the presence of Jovian electrons in interplanetary space as much as 1 AU inside the orbit of Jupiter is summarized. Electron flux patterns at Pioneer 10 can only rarely be correlated with solar activity. Clear variations in intensity and spectrum with a period of 10 hrs are seen at varying distances from Jupiter, consistent with similar observations inside the magnetosphere. Extrapolated electron flux maxima and minima are in good agreement with the observed phase at distances as large as 80 million km from Jupiter, indicating rapid propagation of electrons from the planet. Anisotropy is greatest during the rising phase of the 10 hr variations and in a direction consistent with the interpretation of electrons traveling toward the sun along interplanetary spiral field lines. The propagation time calculated by Chenette's derivation is much larger than that implied by the data.

Chenette, D. L.↗
NASA NTRS1974

Bursts of relativistic electrons from Jupiter observed in interplanetary space with the time variation of the planetary rotation period

Bursts of Jovian electrons in the energy range 3 to 30 Mev have been detected to distances of the order of 1 AU from the planet. The duration of each burst was about two to three days, and the maximum intensity increased with increasing distance from the sun. These events could not be correlated with known solar activity. The conclusion that these electrons originated at Jupiter and were accelerated within the Jovian magnetosphere is based on observations of three of these bursts. The power spectrum of the temporal variations of the 6- to 30-MeV electron flux showed a persistent peak at Jupiter's rotation frequency (corresponding to the ten hour rotation period) out to distances greater than 100,000,000 km from the planet. The slope, or spectral index, of the differential energy spectrum measured as a function of time displayed the ten-hour cyclic variation in the value of the index, which was earlier found to be characteristic of the electrons within the Jovian magnetosphere.

Chenette, D. L.↗