Terrestrial planets around main sequence stars and the cold start problem

Newly developed technology allows us to explore planets beyond our solar system and started the hunting for other habitable worlds. Thus, exoplanetary research is a fast growing field and next generation satellites will not only increase the number of newly detected exoplanets but will also be able to detect biosignatures in their atmospheres - the hint for possible life as we know. The search for habitable worlds is an interdisciplinary work and computer simulations of such planets are of major interest. These simulations help us to understand in which distance to the host star planets might be found with the potential to harbour life: the so-called habitable zone. Furthermore, they give insights to the planetary dynamics such as atmospheric and oceanic circulations. Previous studies have estimated the habitable zone for different star types using simple energy balance models. Many other studies have used various models of different complexity to show the influence of the host stars spectral range for specific planetary configurations. However, comprehensive simulations with intermediate and complex computer models are still missing. Contrary to simple energy balance models, complex computer models explicitly consider physical processes such as various radiation processes, atmospheric and oceanic circulation. These simulations are necessary for future exoplanetary satellite projects. The increasing performance of computer clusters allow us to carry out such simulations in a reasonable overhead for the first time.The research plan focuses on planets around main sequence stars and includes three first author papers (three tasks): (i) «System dynamics of terrestrial planets around main sequence stars», (ii) «Multistability of terrestrial planets around main sequence stars», and (iii) «Cryoplanets and the cold start problem».The first task will investigate the influence of the basic parameters such as angular velocity, atmospheric mass, and gravitational acceleration on the atmospheric dynamics of habitable planets under the influence of different star types. For that, a model of intermediate complexity will be used, which has been adapted by the candidate. Some of the required simulations have already been carried out.The second task will reveal the influence of the star type on the climate state of water rich planets. It will show which climate states are possible and exhibits the characteristic of multistability for different star types. For that, the obliquity/stellar-irradiance parameter space will be sampled for F, G, K, and M stars. In the case of the G star, results can be compared to previous results of the candidate allowing to characterise the model dependency of the results. The second task will help to define the habitable zone around different star types also under the aspect of the cold start problem: A young star has a lower irradiance than in its later stages and, thus, water rich planets may remain in an inhabitable cryoplanet state due to the sea-ice albedo feedback.The third task will focus on the cold start problem itself. The purpose is to reveal how likely water rich planets can escape from a cryoplanet state to a habitable climate state around different star types (F, G, K, and M stars). This is an interdisciplinary study involving paleoclimatology and, in general, habitable exoplanets. The results of this study will reveal how likely a planet in the habitable zone might be in a habitable climate state.For the tasks (ii,iii), the candidate will adapt the NASA GISS model for different main sequence stars. The model used in task (i) will also serve as comparison with the NASA GISS model and might be used for the tasks (ii,iii) in the case of technical problems with the NASA GISS model.