The inner edge of Saturn's B ring

Abstract

The sharp, 90-km wide transition from an optical depth of 0.2 in the C ring to 1 in the B ring begins at 91,970 km from Saturn's center. This radius is found to be almost exactly at the inward stability limit of charged particles launched in the ring plane at the local Kepler velocity, provided these particles have large charge to mass ratio. The zonal harmonic models of Saturn's magnetic field from the Voyager data and the gravitational field model from Pioneer data are essential to get the very close agreement between theory and observation. The theoretical stability limits are 91,973 + 145 km from Voyager 1 magnetic field data and 91,991 ñ 145 km from Voyager 2 magnetic data. The zonal harmonic magnetic field lines are not perpendicular to the ring plane. Therefore, in addition to the magnetic mirror, gravitational, and centrigual forces, an unknown force must be postulated to produce equilibrium in the ring plane and make the stability calculation meaningful.

Saturn ring rain: Model estimates of water influx into Saturn’s atmosphere

“…Two points are immediately evident from the figure. First, there is 504 a local maximum of ring rain influx at ~1.52 R S , near the edge of the instability radius, consistent 505 with predictions (e.g., Northrop and Hill, 1983). Second, the north-south asymmetry in derived 506 water influxes is even more obvious when plotted together; the southern water fluxes dominate 507 all of the equatorial structure.…”

Exospheres and Atmospheric Escape

“…Given the small northward shift (∼ 0.04R S ) of the magnetic dipole center, (Bouhram et al 2006) O + 2 ions will be formed in a disc-like region below the magnetic equator. The speed of corotation becomes smaller than the neutral orbit speed within ∼ 1.86R S , therefore pick-up ions formed at smaller distances from Saturn can be pulled into the southern hemisphere of Saturn (Luhmann et al 2006a; see also Northrop and Hill 1983;Ip 1983aIp , 1984b as suggested by the 2 nd and 3 rd panels in Fig. 7.…”

Latitudinal variation of Saturn photochemistry deduced from spatially-resolved ultraviolet spectra

“…First, the marginal stability radius of charged particles moving with Keplerian velocity in the ring plane, 1.52 × R s , coincides precisely with the inner edge of the B ring (Northrop and Hill, 1983;Northrop and Connerney, 1987). Hence, they interpreted the sharp difference in surface mass density between the C and B rings as indirect evidence for the occurrence of this electromagnetic erosion mechanism.…”

“…These grains or molecules, ionized by the surrounding plasma, become unstable inside a marginal stability radius Hill, 1982, 1983;Ip, 1983Ip, , 1984 where they must necessarily fall towards the planet along the magnetic field lines. As the marginal stability radius, 1.52 × R s , coincides with the inner edge of the B ring, Northrop and Hill (1983) and Northrop and Connerney (1987) interpreted the sharp difference in surface density between the C and B rings as indirect evidence for this mechanism. Moreover, Connerney and Waite (1984) proposed that Saturn's puzzling ionospheric electron densities could be explained with an influx of water from the rings.…”