Imaging solar-terrestrial interactions on the global scale: The SMILE mission

A key link in the Sun – Earth connection is the solar wind coupling with the terrestrial magnetosphere. Mass and energy enter geospace via dayside magnetic reconnection; reconnection in the tail leads to release of energy and particle injection deep into the magnetosphere, causing geomagnetic substorms. The end product of these processes is the visual manifestation of variable auroral emissions. These have been observed both from the ground and from space, the latter for relatively short continuous periods of time. In situ measurements by a fleet of solar wind and magnetospheric missions, current and planned, can provide the most detailed observations of the plasma conditions both in the incoming solar wind and magnetospheric plasma. However, we are still unable to quantify the global effects of the drivers of Sun - Earth connections, 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. We are now able to take a novel approach to global monitoring of geospace: 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, first observed at comets, and subsequently found to occur in the vicinity of solar system planets, including the Earth's magnetosphere. This is where SMILE (Solar wind Magnetosphere Ionosphere Link Explorer) comes in.

SMILE is a novel self-standing mission dedicated to observing the solar wind – magnetosphere coupling at Earth 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. SMILE will provide scientific data on solar wind – magnetosphere interaction at the global level while monitoring it continuously for long, uninterrupted periods of time from a highly elliptical northern polar orbit.

SMILE is a collaborative mission between ESA and the Chinese Academy of Sciences that was selected in Nov. 2015, adopted into ESA’s Cosmic Vision Programme in March 2019, and is due for launch at the end of 2024. The novel science that SMILE will deliver, the ongoing technical developments and scientific preparations, and the current status of the mission, will be presented.