The Carrying Capacity of the Solar Wind: Applications to Ion Escape

Abstract We present a physically motivated analytic framework for estimating solar wind mass-loading rates from ion sources using a simplified “particles in a box” (PIB) model. By applying conservation of energy and conservation of magnetic flux, we derive a general equation for the global pickup ion rate that explicitly accounts for both kinetic and electromagnetic (Poynting) energy fluxes supplied by the upstream wind and distributed to downstream particles and fields. Our analysis reveals that the global pickup rate may be fundamentally constrained by upstream wind parameters and the geometry of the interaction in a nontrivial manner. We further derive a theoretical upper limit to the maximum mass flux that a super-Alfvénic wind can transport. We call this limit the carrying capacity; it is an inherent property of the wind. We apply this framework to the Giotto flyby of Grigg–Skjellerup, and to unmagnetized and weakly magnetized terrestrial planets. The results suggest that the PIB framework may provide a useful big-picture approach for understanding and estimating stellar wind ion pickup in cometary and planetary environments inside and out of the solar system.