Dottorato in ASTRONOMIA

Titolo della tesi: Planetary environments: exosphere modelling and a new particle detection study

The thesis presents a study of the Mercury and Earth exospheres. For Mercury, we study and model the source and loss processes of the exosphere and compare the simulation results with observational data. For the Earth, we focus on the investigation of interactions between the plasma and Earth’s exosphere using the Energetic Neutral Atom (ENA) imaging technique, studying and testing a new ENA detector generation. We use the 3D Monte Carlo model of the Hermean exosphere from Mura et al. (2007) to investigate Mercury’s exosphere. In detail, we upgrade the model to better describe the Micro-Meteoroids Impact Vaporization (MMIV) process as source of Mercury’s Ca. The in-situ observations of Mercury’s Ca exosphere, performed during the MESSENGER/NASA mission, exhibited very high energies, with a scale height consistent with a temperature > 50,000 K, originated mainly on the dawn-side of the planet. It was suggested that the originating process is due to MMIV, but previous estimations were not able to justify the observed intensity and energy. The most likely origin of this exospheric element may be a combination of different processes involving the release of atomic and molecular surface particles. We simulate the 3-D spatial distribution of the Ca-bearing molecule and atomic Ca exospheres generated through the MMIV process including the meteor stream contribution from comet 2P/Encke. We show that the morphology and intensity of the Ca exosphere are consistent with the available MESSENGER observations if we consider a cloud quenching temperature < 3750 K. The comet contribution seems to be underestimated and requires further investigations. Our results can be useful in the exospheric studies and in the interpretation of active surface release processes, as well as in the exosphere observations planning for the ESA-JAXA BepiColombo mission that will start its nominal mission phase in 2026. With the aim to have a complete picture of the solar wind-magnetosphere-exosphere interactions in the Earth’s environment, we investigate the expected ENA signals for a possible instrument on board a LEO spacecraft. We focus on the gas detector, used for the őrst time for ENA applications, and realize a model to simulate the sensor baseline and its performance. A prototype of this new generation ENA detector for space instruments has been tested in Ion-ENA beam facility at the IAPS (Institute for Space Astrophysics and Planetology) in Rome, demonstrating the capability of our setup to detect ions and ENA particles in a low energy range at low pressure. The successful demonstration of the feasibility of this innovative instrument for ENA/Ion detection makes it extremely attractive for a future space mission.