SMuK 2021 – wissenschaftliches Programm
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SYEP: Symposium What makes an exoplanet habitable
SYEP 1: What makes an exoplanet habitable
SYEP 1.1: Hauptvortrag
Mittwoch, 1. September 2021, 14:00–14:30, Audimax
Requirements for Earth-like habitats — •Helmut Lammer — Austrian Academy of Sciences, Space Research Institute, Schmiedlstr. 6, 8042 Graz, Austria
Factors such as stellar and geophysical conditions that allow complex multi-cellular life forms to originate on terrestrial planets with N2-O2-dominated atmospheres, so-called Class I habitats, will be discussed. Recent findings on how earliest accretion processes set the initial parameter stages for terrestrial planets to end up as a Class I habitat are also addressed. Here, the focus will be i) on the lifetime of the protoplanetary disk, how fast a protoplanet can accrete mass within the gas disk so that Earth-size/mass planets may end up inside the habitable zone as sub-Neptunes with H2-He-dominated atmospheres, and ii) on the availability of the initial amount of heat producing radioactive elements such as 40K, 238U, and 232Th on early planets. These elements determine the heat production budget of a planet, which exerts a first order control on its thermal evolution, tectonics, and hence its likelihood for habitability. Since all three elements can be lost during planet formation, compared to Earth one can expect a wide diversity of planets inside the habitable zone with different heat budgets and tectonic regimes, resulting most likely in CO2-dominated atmospheres. Finally, a new formula for the estimation of the number of possible Class I habitats in the Galaxy, which can be fine-tuned and constrained by the detection of main atmospheric constituends, obtained from future space and large ground-based telescopes, will be presented.