Supervisors info:
Νεκτάριος Βλαχάκης, Αναπληρωτής Καθηγητής, Τμήμα Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Summary:
The goal of this Master's Thesis is to propose a methodology to assess planetary habitability for any newly discovered exoplanet lying in the habitable zone of a low mass, superflare, main-sequence star. While habitability is usually a function of multiple parameters (i.e. the size of the planet, the composition of its atmosphere, the existence of liquid water, orbital or rotational dynamics), our method primarily focuses on stellar activity and its effects on potentially existing planetary magnetospheres stemming from dynamo-generated magnetic fields. Our methodology applies to two regimes, relying on whether the exoplanet of interest is tidally locked or unlocked to its mother star. In the former case, a ratio between a conditional (Beq) and a best-case equatorial planetary magnetic field (Bstev), is calculated. A smaller-than-unity value of this ratio favors the formation of a stable atmosphere, possibly adequate to host surface, atmosphere-dependent habitability. In the latter case (tidally unlocked regime), a ratio between a conditional (Beq) and the terrestrial magnetic field (Bearth) is estimated, which indirectly implies how easy or hard it is for an exoplanet to sustain an atmosphere. For a ratio's value lower than unity, surface habitability is favored under the condition that the planet has an equatorial magnetic field at least as strong as the terrestrial one. On the other hand, a value higher than one casts doubts on surface habitability, because even a strong, terrestrial magnetic field is not sufficient to secure an atmosphere for the exoplanet. Both ratios concerning the two different regimes of our method's applicability are based on the observed mother star's activity and are calculated in order to deduce, if the compression of the magnetosphere exceeds the critical distance of two planetary radii below which, atmospheric erosion phenomena are assumed to start taking place.
Keywords:
Planetary surface habitability, tidally locked exoplanets, coronal mass ejections (CMEs), superflare stars, habitable zone, atmospheric erosion, dynamo-generated magnetic fields, compression of magnetosphere
