Plasma transport and magnetic flux circulation in Saturn's magnetosphere

Abstract

The magnetospheres of outer planets are very different than the terrestrial magnetosphere. The magnetosphere of Saturn is rapidly rotating, and has its own plasma source. Enceladus located around 4Rs is the main source of plasma. The strong magnetic field of Saturn's magnetosphere picks up the plasma which experiences a strong centrifugal force in the non-inertial reference frame. The plasma produced in the inner magnetosphere has to be transported radially outward and lost to the solar wind. The transport of plasma in Saturn's magnetosphere is not fully understood. It is believed that transport is centrifugally-driven, occurring via flux tube interchange motions in the inner magnetosphere and via plasmoid expulsion in the magnetotail due to reconnection. It has been found that these mechanisms are not sufficient to explain the transport. We tried to determine different possible transport mechanisms that could exist in the outer planetary magnetosphere. Ma et al. (2019a) showed the low-specific entropy plasma with a narrow distribution in Saturn's inner magnetosphere and suggests a significant nonadiabatic cooling process during the inward motion while high specific entropy suggests the nonadiabatic heating during the outward transport. We have estimated the outward plasma transport rate about 55 kg s⁻¹. The calculation of magnetic flux transport and analysis of magnetic field data indicates that plasma transport in the Saturn magnetosphere could be dominated by small scale magnetic reconnection.