Die Beschreibung der Entwicklung von deuteriertem Wasser mithilfe eines Multi-Zustandsmodells des Solaren Nebels

Kurzfassung

Many definitions of habitability rest on the availability of liquid water, but it is still an open question where planetary water actually comes from. Recently it has been con- firmed that it already exists within grand molecular clouds, which are nurseries for stellar formations, along with certain prebiotic molecules. Within the Solar Nebula hypothesis the metastable hydrostatic cores of these clouds collapse while building up a disk around their equatorial plane of rotation to redistribute their angular momentum. Based on this temporal evolution this work seeks to model the transport and chemical evolution of the matter accreted by the protostar during the three stages of the Solar Nebula in an ab-initio approach, so that every stage is initialized by the physical and chemical Parameters of the former. The individual models are a hydrostatic cloud core, a semianalytic adiabatic collapse and a disk model, including detailed dust convection. The chemistry is treated in a Lagrangian approach by combining the before mentioned models with a gas-grain chemistry model. The main focus is on the distribution of water and ist deuterated counterparts since the D=H ratio can give important clues about the origin and history of cometary and planetary water reservoirs. The results suggest that water is a robust phenomenon within the cloud stage and is relatively insensitive to variations in the external radiation and dust migration in its envelope. The highest fraction of deuterated water is located in the deeply embedded core region with a D/H value of at most 2.2%. Meanwhile, the overall water concentration is found to be almost constant along the radial extent of the core, mainly carried by ice coated grains. Towards the end of the collapse of the cloud core a \hot corino" zone builds up with a diameter of less than 1.4 astronomical units. The beginning neutral-neutral reactions in this Zone can not jet change the deuteration significantly, leading to a radially constant value of D/H ~ 2.5% in the disk build up region. Due to the adiabatic nature of the collapse, the resulting disk has a very low temperature gradient which also leads to other deviations from the expected MMSN structure. The continuous initialization of the chemical disk composition has been hindered by the absence of a vertical representation in the collapse phase. In the future this can be improved by adding an intermediate thick disk model.