Analyses of Voyager 1 radio occultation measurements of the Saturn atmosphere near 75 deg south latitude and of the Titan equatorial atmosphere are presented. Molecular nitrogen appears to be the primary atmospheric constituent of Titan, whose clouds are probably methane ice. Solar abundance considerations of the data suggest large quantities of surface methane near its triple-point temperature, so that the three phases of methane could play a role on Titan analogous to that of water on earth. Ionospheric electron concentration and plasma scale height for the Saturn polar cap and monochromatic attenuation of the Saturn rings are also considered, along with radio tracking figures for the masses of two moons, Rhea and Titan.

http://science.sciencemag.org/content/sci/212/4491/201.full.pdf

Radio science investigations of the saturn system with voyager 1: preliminary results.

The solar wind plasma analyzer on board Pioneer 2 provides first observations of low-energy positive ions in the magnetosphere of Saturn. Measurable intensities of ions within the energy-per-unit charge (E/Q) range 100 eV to 8 keV are present over the planetocentric radial distance range about 4 to 16 R sub S in the dayside magnetosphere. The plasmas are found to be rigidly corotating with the planet out to distances of at least 10 R sub S. At radial distances beyond 10 R sub S, the bulk flows appear to be in the corotation direction but with lesser speeds than those expected from rigid corotation. At radial distances beyond the orbit of Rhea at 8.8 R sub S, the dominant ions are most likely protons and the corresponding typical densities and temperatures are 0.5/cu cm and 1,000,000 K, respectively, with substantial fluctuations. It is concluded that the most likely source of these plasmas in the photodissociation of water frost on the surface of the ring material with subsequent ionization of the products and radially outward diffusion. The presence of this plasma torus is expected to have a large influence on the dynamics of Saturn's magnetosphere since the pressure ratio beta of these plasmas approaches unity at radial distances as close to the planet as 6.5 R sub S. On the basis of these observational evidences it is anticipated that quasi-periodic outward flows of plasma, accompanied with a reconfiguration of the magnetosphere beyond about 6.5 R sub S, will occur in the local night sector in order to relieve the plasma pressure from accretion of plasma from the rings.

/pdf/plasmas-in-saturn-s-magnetosphere-19cc0yjfms.pdf

Plasmas in Saturn's magnetosphere

It is inferred from observation of an occultation of the sun by Titan, using the Voyager 1 UV spectrometer, that temperatures are 176 + or - 20 K near the evening terminator and 196 + or - 20 K near the morning terminator, and that the major atmospheric constituent is N2, with a density of 2.7 + or - 0.2 x 10 to the 8th/cu cm at 3840 km. A layer of absorbing molecules, possibly polymers, is found near both morning and evening terminators. A photochemical model suggests that the homopause is located at 3500 + or - 70 km, with an eddy diffusion coefficient of 1(+2, -0.7) x 10 to the 8th/sq cm per sec, which decreases to about 1000 sq cm/sec in the lower stratosphere as N2 to the -2/3 power.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JA087iA03p01351%4010.1002/%28ISSN%292169-9402.TITAN2

Titan's upper atmosphere: Composition and temperature from the EUV solar occultation results

Results of Pioneer 11 imaging photopolarimeter observations of Saturn, its rings, and Titan are presented. The imaging photopolarimeter is a pointable telescope with an aperture of 2.5 cm and passbands of 390 to 500 to 720 nm which uses the spin of the spacecraft to scan across an object. Images of the Saturn system and of the rings are presented, and the absence of a D ring, structures in the C, B and A rings and the Cassini division and the discoveries of the F ring and the provisionally named Pioneer division separating it from the A ring are reported. A mean particle size less than 15 meters is estimated from estimates of total ring mass and the optical depth of the B ring. The discovery of the satellite 1979 S 1 at 2.53 Saturn radii is also noted. Models of the vertical aerosol structure of Saturn's atmosphere are compared with the polarization data, and it is indicated that the density of cloud particles decreases with altitude with a scale height about one fourth that of the gas, and that an optical depth of one is to be found at 750 mbar.

https://science.sciencemag.org/content/sci/207/4429/434.full.pdf

Imaging photopolarimeter on pioneer saturn.

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.

The Trapped Radiations of Saturn and Their Absorption by Satellites and Rings

During the Pioneer Saturn encounter, a continuous round-trip radio link at S band ( approximately 2.2 gigahertz) was maintained between stations of the Deep Space Network and the spacecraft. From an analysis of the Doppler shift in the radio carrier frequency, it was possible to determine a number of gravitational effects on the trajectory. Gravitational moments ( J(2) and J(4)) for Saturn have been determined from preliminary analysis, and preliminary mass values have been determined for the Saturn satellites Rhea, Iapetus, and Titan. For all three satellites the densities are low, consistent with the compositions of ices. The rings have not been detected in the Doppler data, and hence the best preliminary estimate of their total mass is zero with a standard error of 3 x 10(-6) Saturn mass. New theoretical calculations for the Saturn interior are described which use the latest observational data, including Pioneer Saturn, and state-of-the-art physics for the internal composition. Probably liquid H(2)O and possibly NH(3) and CH(4) are primarily confined in Saturn to the vicinity of a core of approximately 15 to 20 Earth masses. There is a slight indication that helium may likewise be fractionated to the central regions.

https://science.sciencemag.org/content/sci/207/4429/449.full.pdf

Joseph J. Macfarlane

Papers

Pioneer Saturn Celestial Mechanics Experiment