Helmut Lammer: The evolution of Earth-like habitats

Professor in Planetary Sciences at the Space Research Institute in Graz, Austria.

His long research career concentrates around planetary physics, including studies of atmospheric escape processes, evolution of planetary and exoplanetary environment, and habitability of exoplanets.

Helmut Lammer's professional web-site

Abstract: The talk will address the most important astrophysical and geophysical factors necessary for Earth-like Habitats (EH) with N2/O2-dominated atmospheres inside the habitable zone for complex life (HZCL). It will be explained that the lifetime of the disk and accretion processes of the growing protoplanets set the initial parameter stages for terrestrial planets so that they can end up as EHs. A competition between the time scales of the gas disk and the planetary accretion will determine if an accreting terrestrial planet may end inside the HZCL as a planet with an H2/He dominated atmosphere, or not. Other relevant factors like a planet's thermal evolution and hence the right tectonic regime that is necessary for aerobic lifeforms as we know it will also be addressed. One can expect that many terrestrial planets inside the HZCL will have internal heat budgets and tectonic regimes that are different than those of Earth. Nitrogen is a necessary element in the building blocks of life; therefore, the geobiological N2-cycle and a functioning C-cycle are fundamental factors in the long-term evolution of EHs. Thus, terrestrial planets with N2/O2-dominated atmospheres will have a tectonic regime and will be a strong indication for an aerobic biosphere. Tectonic regimes that do not allow or maintain N2/O2-dominated atmospheres for billions of years are very likely to produce Venus- or Mars-like CO2-dominated atmospheres which will be not be life-friendly for aerobic complex lifeforms. Finally, a newly derived formula that can be used to estimate the potential numbers of EHs in the galaxy, will also be discussed.