Hermean environment

WP1520 aims to study the effects of SWE on the planet Mercury.

Mercury, in fact, possesses a weak nearly bipolar magnetic field, similar to the Earth one, and a very tenuous atmosphere (technically named ‘exosphere’) that directly exposes it to the solar and interplanetary interactions. Hence, the Mercury’s exosphere and magnetosphere directly interact with the IMF (interplanetary magnetic fields) and with the SWE.

In particular, the sodium component of the exosphere is a marker of the direct interaction of the plasma with the planet, through the many processes of ionization, release and loss related to the magnetic field, and solar radiation. As a consequence, the sodium exosphere shows a recurrent 2-peak-pattern at high latitude, in a region that could be addressed as the footprints of the planetary magnetic cusps, and shows also a high variability in intensity and spatial position of the patterns, that may also disappear or collapse into a single peak in the equatorial subsolar region.

The image shows an artistic view of the magnetosphere of Mercury with its dipolar field lines, and the exosphere in the solar and anti-solar direction (tail, in red). Superposed to the planetary disk is the typical exospheric sodium pattern, as obtained from Earth-based observations, with its two peaks of intensity at high latitude in the sub-solar direction, in the region of the magnetospheric cusps. In yellow, the bow shock.(from www.serena.iaps.inaf.it)

The comprehension of Mercury exosphere structure and dynamics is then a mean to study the space weather at other sites than the Earth. This goal can be achieved through the combination of Na exospheric data and exospheric simulations to account for the many possible morphologies and IMF-intrinsic magnetic field coupling. In particular, we will provide:

  • Data: a wide data-set of sodium exospheric density maps at different periods and different orbital and solar conditions, as observed from the solar telescope THEMIS in the Canary Islands in the years 2007-2014;
  • Simulations: simulations of the precipitation of SW protons onto the surface of Mercury, by using the Magnetospheric ion circulation and precipitation model by Massetti et al. (2003, 2007) at different IMF external conditions to be used as inputs for a reduced version of the Exospheric model by Mura et al. (2005, 2009) that can perform real-time Montecarlo simulations of the exosphere of Mercury depending on the user-provided input parameters (i.e. magnetospheric external conditions, orbital/seasonal position, surface temperature and chemical composition, characteristics of the release processes).