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

Abstract

The Pioneer 11 spacecraft encounter with Saturn (closest approach September 1, 1979) has resulted in the discovery of a fully developed magnetosphere with high-energy trapped radiation around Saturn, as reported in Science, 207, 400-453, 1980, by several investigators with charged-particle instruments on the spacecraft. The present paper contains in detail the final energetic charged-particle measurements and new observations obtained from the University of Chicago instrumentation on Pioneer 11, including the overall characteristics of the trapped electron, proton, and helium radiation, which was found to lie inside ~20 Saturn radii (Rs) from the planet, and the regions extending outward to beyond the planetary bow shocks and into the interplanetary medium. For analytical purposes we divided the magnetosphere into an inner magnetosphere (<5 Rs), where the intensity profiles displayed the near-axial symmetry characteristics of the dipole magnetic field alignment with the spin axis, and an outer magnetosphere whose characteristics on the sunward side inbound were significantly different from the dawn side outbound, indicative of a possible magnetotail but with no dramatic evidence in the charged-particle data for an equatorial current sheet, as observed at Jupiter. The intensities and energy ranges of the protons and electrons were intermediate between the levels found previously at Jupiter by Pioneer 10 and 11 and at earth. Energy spectra for protons and electrons and relative abundances of protons and helium nuclei are presented along with the average characteristics of particle anisotropies. At the time of encounter the magnetosphere was immersed in intense fluxes of electrons, protons, and helium nuclei of solar flare origin which are shown to penetrate from I Rs to 10 Rs into the magnetosphere, where they dominated the flux levels in the far outer magnetosphere. A corotation anisotropy has been measured at the proton energy ~ 1 MeV in the rotating magnetosphere after correcting the observed unidirectional anisotropy for the radial gradient of the proton flux. The principal focus of the paper is on the analysis of the trapped radiation in the inner magnetosphere, where the radiation reaches high intensity, and has a high degree of symmetry in the L shells around Saturn. Consequently, the absorption signatures in the radiation intensity profiles produced by tings and moons of Saturn can be analyzed quantitatively. Among other resuits the observation of the charged-particle absorption features have led to the discovery of satellite 1979 S2 at L --2.53, which corresponds with the optically detected 1979 S I, a concentration of matter probably located at a Lagrangian point in the orbital range of Mimas, and the identification of narrow rings of matter and one or more satellites inside the radial range of the F ring discovered by the optical-imaging investigators. It is pointed out that these discoveries will provide important tests for models of accretion of matter, satellite formation and the stability of narrow r...

Magnetosphere Imaging Instrument (MIMI) on the Cassini Mission to Saturn/Titan

“…The critical influence of such materials as dust, rings, and satellite surfaces on the character of the energetic particle populations is shown most clearly in Figure 5 ( Simpson et al, 1980). Dust particulates of the F, G, and E-rings clearly have roles to play, as do both the larger particles of the A and F rings and the satellites.…”

“…However, the ENA imaging capabilities of INCA, combined with the information of energy spectra, angular distribution, and charge state obtained with LEMMS and CHEMS, provides a powerful new technique for diagnosing ring-particulate/energetic-particle interactions, as described below. Simpson et al, 1980). The intense populations of magnetically trapped, energetic charged particles that constitute the radiation belts of Saturn's inner magnetosphere are slowly transported towards the planet by radial diffusion processes.…”

Constraints on the interactions between dark matter and baryons from the x-ray quantum calorimetry experiment

“…[46]. The constraints to σ Dn from Pioneer 11 [80], Skylab [81], and IMP7/8 [82] were interpreted by Refs. [38,46,48].…”

Energization of particles in Saturn's inner magnetosphere: Monte Carlo simulation of stochastic electric field effects

“…The rings and the many large and small satellites in the inner magnetosphere reduce the population of particles whose energies are higher than 0.5 MeV to values of the order of 10 3 times less than would otherwise be present, in other words, the rings and satellites can absorb energetic particles. Some of these absorption microsignatures were reported by Simpson et al (1980), Roussos et al (2005), and Paranicas et al (2005).…”

“…These signatures do weaken with increasing distance from Saturn, hence the varying strengths of the absorptions. For example, some microsignatures have been observed at the orbit of Dione (∼6.3 R S ) and reported by Simpson et al (1980) and, recently, Cassini has detected them at the orbit of Tethys (∼4.8 R S ) (Roussos et al 2005). The effect of the corotation velocity on the energization of particles is an interesting task to investigate, for example in Dione's and Rhea's orbits.…”