The Atmospheres of Super Earths

The subject of this thesis are the atmospheres of Super-Earths. Super-Earths are planets around other stars (so-called exoplanets) with masses larger than Earth and up to 10 Earth masses. Currently, 20 such planets are known. The aim of this work was to address two key questions related to Super-Earth science: Firstly, whether potentially habitable (i.e., life-bearing) exoplanets exist, secondly, whether the atmospheres of such exoplanets could be investigated spectroscopically from Earth. In order to address these questions, a one-dimensional computer model for planetary atmospheres was developed, extensively tested, validated and compared to other published work. The model has then been applied to the exoplanet Gliese 581 d. Gliese 581 d is a Super-Earth and currently the only known exoplanet which is potentially habitable. With the atmospheric model, a parameter study was performed where the surface pressure and the CO2 concentration have been varied. It was shown that for high surface pressures (5 bar and more for 95 % CO2, 20 bar and more 5 % CO2), calculated surface temperatures were higher than 273 K (melting point of water), hence such atmospheric scenarios result in habitable conditions. Scenarios with less surface pressure or less CO2 concentration were found to be uninhabitable. With the results of the atmospheric model, synthetic high-resolution spectra of the planet were calculated to investigate whether habitable conditions could be inferred remotely or whether atmospheric scenarios could be discerned. It was shown that emission spectroscopy is not well suited to investigate surface conditions or atmospheric scenarios. By contrast, with transmission spectroscopy atmospheric scenarios could be characterized much better. Calculating spectroscopic signals of Gliese 581 d, based on planned space observatory performances from the James Webb Space Telescope showed that the expected planetary signals are much too weak to allow for an atmospheric detection. However, in this work it was shown that Gliese 581 d is indeed the rst potentially habitable planet outside our solar system, con rming very recent studies.