Seminar: Atmospheres of rocky exoplanets
Some of the fundamental questions for planetary science are how surfaces of other rocky planets look like. What is the rock composition? Will there be liquid water? And also, what the atmospheres above is composed of, what cloud condensates can be found under various conditions. Which conditions are present and could favour the presence of life? Future instrumentation will allow the investigation of the atmospheres of rocky exoplanets, however the surface conditions will remain very difficult to observe, especially if clouds are present and obstructing the direct view onto the surface. Therefore understanding the link between the upper atmosphere (gas composition, cloud condensates) to the conditions on the crust of the planet (temperature, pressure, rock composition) is crucial. With our bottom-to-top atmospheric models, we investigate atmospheres above various different surface compositions. The atmosphere is in chemical and phase equilibrium with the crust and follows hydrostatic equilibrium. Thermally stable condensates are removed from the atmosphere depleting the effected elements in the atmosphere above. The removed condensates provide an insight to potential cloud condensates which can constrain the surface conditions. The thermally stable condensates fall into two different regimes of high and low temperature condensates, where only Graphite (C[s]) is breaching the different regimes. Water clouds are of special interest, not only because they allow thoughts about aerial biospheres for life as we know it, but water clouds become stable independent on whether or not water is stable at the crust. Therefore water clouds cannot be used as a sole indicator for liquid water at the planetary surface. In order to constrain the potential likelihood of the formation of pre-biotic molecules, we introduce ‘habitability’ levels by taking into account the presence and chemical state of the CHNOPS elements in regions of the atmosphere, where water condensates are present. Our models show that in the surrounding of liquid water condensates the presence of carbon, nitrogen, and sulphur in a reduced form is a common result for various different elemental abundances. However, phosphorus and metals are not available for the formation of life in aerial biospheres and can therefore be seen as limiting elements for the origin of life.