Microphysical cloud models for exoplanets
Zusammenfassung der Projektergebnisse
Within two decades, the field of exoplanetology has broadened our perspective on planetary systems with more than 1800 planets found in over 1100 systems different from ours. Some exoplanets are suspected to be rocky and receive roughly as much stellar irradiation as Earth does. Therefore, it is possible that a subset of exoplanets could harbor liquid water on their surfaces, a crucial ingredient for life as we know it. The region around stars where a planet could harbor liquid water is called the Habitable Zone (HZ). This DFG research project studied where is the inner edge of the HZ, in other words, how close can the HZ be to a host star. This is an important question because planets found beyond the inner edge of the HZ could potentially harbor liquid water on their surfaces, and such planets should be prime candidates for follow-up observational studies that aim to characterize exoplanet atmospheres. I developed a general-purpose 1D vertical climate model from scratch during the project. I used the model to study the surface climate on exoplanets under various stellar, planetary, and atmospheric parameters. It is important to study a wide range of scenarios because exoplanet atmospheres are empirically unconstrained. Such parameters include but are not limited to the stellar mass, planetary surface gravity, atmospheric composition, surface pressure, and relative humidity. I found that a planet at the inner edge of the HZ could harbor liquid water at its polar regions as close as 0.5 AU around a solar-like star, if its atmosphere is nitrogen-dominated and the surface albedo is Marslike. For comparison, such a planet would orbit its star closer than Venus orbits the Sun (0.72 AU). We also presented synthetic transmission spectra of inner edge planets as observed with the James Webb Space Telescope (JWST). We find that JWST will be able to distinguish a Venus-like atmosphere from an Earth-like or Dunelike atmosphere. The transmission spectra of Earth-like and Dune-like atmospheres appear similar. Distinction between these two atmosphere types is possible based on the incoming stellar flux: a Dune-like planet receives roughly four times more stellar flux than an Earth-like planet. The results of the project have been disseminated online and via seminar talks at various research institutions world-wide.
