Colloquium: Anna Shapiro (Max Planck Institute for Solar System Research)
Metal-rich stars are less friendly to life: The UV paradox
Abstract: While the ozone is only a minor component of the Earth’s atmosphere, it is one of the most important species to sustain life on the Earth. It is produced photochemically from molecular oxygen. Both oxygen and ozone protects the biosphere by absorbing harmful UV radiation. In this study we address the intriguing question of what would happen with the ozone layer if the Earth is hosted by another solar-like star instead of the Sun. Namely, we model the atmosphere of an ExoEarth orbiting a solar-like star with different values of metallicity (from -1 to 1 dex) and effective temperature (from 5300 to 6300 K). We show that, paradoxically, although metal-rich stars emit less UV radiation than metal-poor stars, the drop of ozone concentration leads to higher surface UV on their planets. This implies that the Universe gets less life friendly as it ages because stars become more metal-rich. We also study the response of the ozone layer and surface UV to different disturbing factors such as increase of stellar magnetic activity, supernova explosion, volcanic eruptions. We found that while volcanic eruptions are the most ozone destructive hazards, oxidised atmospheres (O2 level higher than 20%) have sufﬁcient buffering capacity to reduce the damage. Furthermore, our calculations indicate that recently proposed events of sudden rise of stellar magnetic activity lead to increase in ozone concentration and, consequently, drop in the surface UV.
Sept. 28, 2023, 2:30 p.m. – 4 p.m.
Schwarzschildhaus Lecture Hall