Wherever lightning occurs, it impacts the chemistry profoundly. Therefore, lightning could have a substantial impact on the chemistry of protoplanetary disks. The link between lightning and protoplanetary disks are charged dust grains, as they are required for lightning to emerge and do appear in the midplanes of protoplanetary disks. Charged dust grains can play a vital role in the planet formation process due to their interaction with the magneto rotational instability, hence understanding their charging behavior in detail could give new insights into the planet formation process.
The main topic of this work is to investigate how dust grains charge in the midplanes of proplanetary disks, how they impact the chemistry and the charge balance and lastly whether they could lead to the emergence of lightning. In order to study the charging behavior of dust grains in protoplanetary disks, I use the thermo-chemical disk model ProDiMo (Woitke et al. [2016]).
I did several improvements to the model, in order to make this study possible. For example I made it possible for the model to consider several different dust grain sizes, where previously the model used a single average dust grain size. Additionally I implemented a new approach in the charging chemistry of ProDiMo where we can now handle triboelectric charging in conjunction with the other charging mechanisms, such as photoionization, electron attachment and charge exchanges between dust grains and molecules. This approach of combining triboelectric charging and other charging mechanism is a completely new approach in the field.
The main findings of this study is that in the midplanes of protoplanetary disks the dust grains become the dominant negative charge carrier and together with NH4+ dominate the charge balance.
Using these results, I developed a simple turbulence driven charge separation model in order to test if the conditions that I found in the midplanes could lead to an emergence of lightning. I found that the electric fields generated in this way are not large enough for an electron avalanche to occur. An electron avalanche is mandatory for lightning to occur.
In addition, this work will show some preliminary results of the implementation of triboelectric charging. The main finding is that the dust charging distribution can change significantly if one considers triboelectric charging.
Lastly, this work also discusses my involvement in the MSG project (Jørgensen et al.) and the work I did in implementing non-equilibrium chemistry into the MARCS code. In particular, I test the impact of the Chapman cycle on the upper atmospheres of a simulated exoplanet.