Centrifugally stimulated exospheric ion escape at Mercury

We investigate the transport of ions in the low-altitude magnetosphere of Mercury. We show that, because of small spatial scales, the centrifugal effect due to curvature of the E×B drift paths can lead to significant particle energization in the parallel direction. We demonstrate that because of this effect, ions with initial speed smaller than the escape speed such as those produced via thermal desorption can overcome gravity and escape into the magnetosphere. The escape route of this low-energy exosphere originating material is largely controlled by the magnetospheric convection rate. This escape route spreads over a narrower range of altitudes when the convection rate increases. Bulk transport of low-energy planetary material thus occurs within a limited region of space once moderate magnetospheric convection is established. These results suggest that, via release of material otherwise gravitationally trapped, the E×B related centrifugal acceleration is an important mechanism for the net supply of plasma to the magnetosphere of Mercury.