A Novel and Global Way to Explore Solar-Terrestrial Interactions: SMILE

The coupling between the solar wind and the Earth's magnetosphere-ionosphere system, and the geospace dynamics that result, comprise some of the key questions in space plasma physics. In situ measurements by a fleet of solar wind and magnetospheric missions, current and planned, can provide the most detailed observations of the Sun-Earth connections. However, we are still unable to quantify the global effects of the drivers of the solar wind-magnetosphere-ionosphere coupling, and to monitor their evolution with time. This information is the key missing link for developing a comprehensive understanding of how the Sun gives rise to and controls the Earth's plasma environment and space weather.

SMILE (Solar wind Magnetosphere Ionosphere Link Explorer) is a novel self-standing mission dedicated to observing the solar wind - magnetosphere coupling via simultaneous X-ray imaging of the magnetosheath and polar cusps (large spatial scales at the magnetopause), UV imaging of global auroral distributions (mesoscale structures in the ionosphere) and in situ solar wind/magnetosheath plasma and magnetic field measurements. X-ray imaging of the magnetosheath and cusps is made possible by the X-ray emission produced in the process of solar wind charge exchange (SWCX), first observed at comets, and subsequently recognized as a ubiquitous phenomenon arising from the encounter of the solar wind with planetary exospheres and magnetospheres. One of the science aims of SMILE, operating in a highly elliptical Earth polar orbit, is to track the geomagnetic substorm cycle via SWCX X-ray imaging of the dayside magnetosheath, by monitoring the location of the magnetopause and by following the substorm consequences on the aurora with UV imaging.