  At Mercury, several processes can release ions and neutrals out of the
planet's surface. Here we present enhancements of dayside planetary ions in the
solar wind entry layer during flux transfer event (FTE) "showers" near
Mercury's northern magnetospheric cusp. The FTE showers correspond to the
intervals of intense magnetopause reconnection of Mercury's magnetosphere,
which form a solar wind entry layer equatorward of the magnetospheric cusps. In
this entry layer, solar wind ions are accelerated and move downward (i.e.
planetward) toward the cusps, which sputter upward-moving planetary ions within
1 minute. The precipitation rate is enhanced by an order of magnitude during
FTE showers and the neutral density of the exosphere can vary by >10% due to
this FTE-driven sputtering. These in situ observations of enhanced planetary
ions in the entry layer likely correspond to an escape channel of Mercury's
planetary ions, and the large-scale variations of the exosphere observed on
minute-timescales by Earth observatories. Comprehensive, future multi-point
measurements made by BepiColombo will greatly enhance our understanding of the
processes contributing to Mercury's dynamic exosphere and magnetosphere.
