Saturn as a radio source
Magnetospheric radio emissions, Saturn electrostatic discharges, inferred source locations, and emission theories are addressed.
Kaiser, M.L.↗
Engineering topics
Lecacheux, A.
Publications and source records attributed to Lecacheux, A..
Planetary radio astronomy observations from Voyager 2 near Saturn
Planetary radio astronomy measurements obtained by Voyager 2 near Saturn have added further evidence that Saturnian kilometric radiation is emitted by a strong dayside source at auroral latitudes in the northern hemisphere and by a weaker source at complementary latitudes in the southern hemisphere. These emissions are variable because of Saturn's rotation and, on longer time scales, probably because of influences of the solar wind and Dione. The electrostatic discharge bursts first discovered by Voyager 1 and attributed to emissions from the B ring were again observed with the same broadband spectral properties and an episodic recurrence period of about 10 hours, but their occurrence frequency was only about 30 percent of that detected by Voyager 1. While crossing the ring plane at a distance of 2.88 Saturn radii, the spacecraft detected an intense noise event extending to above 1 megahertz and lasting about 150 seconds. The event is interpreted to be a consequence of the impact, vaporization, and ionization of charged, micrometer-size G ring particles distributed over a vertical thickness of about 1500 kilometers.
Warwick, J. W.↗
Planetary radio astronomy observations from Voyager-2 near Saturn
Voyager-2 planetry radio astronomy measurements obtained near Saturn are discussed. They indicate that Saturnian kilometric radiation is emitted by a strong, dayside source at auroral latitudes in the northern hemisphere and by a weaker (by more than an order of magnitude) source at complementary latitudes in the southern hemisphere. These emissions are variable both due to Saturn's rotation and, on longer time scales, probably due to influences of the solar wind and the satellite Dione. The Saturn electrostatic discharge bursts first discovered by Voyager-1 and attributed to emissions from the B-ring were again observed with the same broadband spectral properties and a 10(h)11(m) + or - 5(m) episodic recurrence period but with an occurrence frequency of only of about 30 percent of that detected with Voyager-1. During the crossing of the ring plane at a distance of 2.88 R sub S, an intense noise event is interpreted to be consequence of the impact/vaporization/ionization of charged micron-size G-ring particles distributed over a total vertical thickness of about 1500 km.
Warwick, J. W.↗
Radio Jupiter after Voyager - An overview of the planetary radio astronomy observations
An overview of Jupiter's low-frequency radio emission morphology as observed by the planetary radio astronomy (PRA) instrument onboard the Voyager spacecraft is presented. The PRA measurement capabilities and limitations are summarized, based on over two years of experience with the instrument. As a direct consequence of the PRA spacecraft observations, unprecedented in terms of their sensitivity and frequency coverage, at least three previously-unrecognized emission components have been discovered: broadband and narrow-band kilometric emission, and the lesser-arc decametric emission. Their properties are reviewed. In addition, the fundamental structure of the decameter wavelength and hectometer wavelength emission, now believed to be almost exclusively in the form of complex but repeating arc structures in the frequencytime domain, is described. Dramatic changes in the emission morphology of some components as a function of the sun-Jupiter-spacecraft angle (local time) are described. Finally, the PRA in situ measurements of the Io plasma torus hot-to-cold electron density and temperature ratios are summarized.
Boischot, A.↗
Arc structure in Saturn's radio dynamic spectra
It is pointed out that one of the most spectacular findings of the Voyager 1 planetary radio astronomy experiment (PRA) was the discovery of nested arc-like structures in the dynamic spectra of Jupiter's decametric emission. These arcs have curvature in either a direction towards increasing or decreasing time. Similar arc structures are also evident in Saturn kilometric radiation. These structures appear superimposed on the strong intensity modulation which is controlled by the rotation of the planet and on fast and narrow band fluctuations which give a very large variability to the PRA observations on a 6-s, 20-kHz scale. The characteristics of the arcs are examined and compared with the arc structure in Jupiter. The similarities between Saturn's and Jupiter's arc structures are found to imply that they are probably due to the same physical mechanism.
Boischot, A.↗
Saturnian kilometric radiation - Statistical properties and beam geometry
An adequate description of the average statistical properties of Saturn's radio emissions is needed for a study of these emissions. Data regarding these properties are presented, and the implications for source location, beaming, and magnetic surface anomalies are discussed. A description is presented of the average properties of the Saturn kilometric radiation (SKR) as observed from two locations by the Voyager 1 planetary radio astronomy (PRA) instrument for a 2-month period centered on the November 12, 1980 encounter. An analysis of the occurrence pattern of SKR as a function of Saturn's rotation phase has shown that SKR occurrence is not continuous, but variable and roughly periodic. The statistical SKR properties obtained strongly constrain possible source locations. Several source locations are possible, but most intriguing is the region at high latitudes near the noon meridian.
Kaiser, M. L.↗
Planetary radio astronomy observations from Voyager 1 near Saturn
The Voyager 1 planetary radio astronomy experiment detected two distinct kinds of radio emissions from Saturn. The first, Saturn kilometric radiation, is strongly polarized, bursty, tightly correlated with Saturn's rotation, and exhibits complex dynamic spectral features somewhat reminiscent of those in Jupiter's radio emission. It appears in radio frequencies below about 1.2 megahertz. The second kind of radio emission, Saturn electrostatic discharge, is unpolarized, extremely impulsive, loosely correlated with Saturn's rotation, and very broadband, appearing throughout the observing range of the experiment (20.4 kilohertz to 40.2 megahertz). Its sources appear to lie in the planetary rings.
Warwick, J. W.↗
Radio Jupiter after Voyager: An overview of the Planetary Radio Astronomy observations
Jupiter's low frequency radio emission morphology as observed by the Planetary Radio Astronomy (PRA) instrument onboard the Voyager spacecraft is reviewed. The PRA measurement capabilities and limitations are summarized following over two years of experience with the instrument. As a direct consequence of the PRA spacecraft observations, unprecedented in terms of their sensitivity and frequency coverage, at least three previous unrecognized emission components were discovered: broadband and narrow band kilometric emission and the lesser arc decametric emission. Their properties are reviewed. In addition, the fundamental structure of the decameter and hectometer wavelength emission, which is believed to be almost exclusively in the form of complex but repeating arc structures in the frequency time domain, is described. Dramatic changes in the emission morphology of some components as a function of Sun-Jupiter-spacecraft angle (local time) are described. Finally, the PRA in suit measurements of the Io plasma torus hot to cold electron density and temperature ratios are summarized.
Boischot, A.↗
Voyager spacecraft radio observations of Jupiter - Initial cruise results
Low frequency (below 1326 kHz) observations of Jupiter obtained from November, 1977 through June, 1978 by the radio astronomy receivers carried by the two Voyager spacecraft are reported and compared with a large body of higher-frequency ground-based observations. Although the morphology of hectometric wavelength (HOM) emissions strongly resembles that of decametric (DAM) wavelength radio noise, they display opposite polarization. DAM emissions are strongly modulated by Io, whereas HOM emissions exhibit little or no influence from any satellite and appear to be modulated by the rotation phase of the planet. Several single-source models could possibly account for these results, including a model assuming emission at two well-separated frequencies above and below the local electron plasma frequency and the model proposed by Barbosa (1976) in which electrostatic waves at twice the upper hybrid frequency couple to both the ordinary and extraordinary electromagnetic modes. However, neither of these is entirely satisfactory.
Kaiser, M. L.↗
Voyager spacecraft radio observations of Jupiter: Initial cruise results
Jupiter's low-frequency radio emission were detected by the planetary radio astronomy instruments onboard the two Voyager spacecraft. The emission is surprisingly similar in morphology but opposite in polarization to the high-frequency Jovian radio noise that were observed with ground-based telescopes for more than two decades. Several possible explanations for the behavior of the low-frequency emission are examined, but none of them is completely satisfactory.
Kaiser, M. L.↗