Mountains and Deserts in the demographics of Giants (Part I)

The location of giant planets may play a central role on habitability of the terrestrial planets in the same planetary system. As an example, giant planets are thought to play a central role in the delivery of volatiles to terrestrial planets (e.g., Quintana & Lissauer 2014; Sanchez et al. 2018) or stopping the influx of pebbles from the outer disc, possibly preventing the early formation of terrestrial planets (e.g., Ormel et al. 2017). Current exoplanet surveys show a diversity of configurations, but also a number of trends in terms of the distribution of planetary orbits and sizes.  The current DFG priority program on Exoplanets (SPP1992)  focuses on understanding the nature of this diversity, as well as explaining the origins and the consequences of some of the observed trends.
In this project, we explored a possible link between the X-ray properties of host stars and the semi-major axis distribution of warm Jupiters, presumably established in the disc dispersal phase and driven by X-ray photoevaporation from the host star.
In Monsch et al. (2019) we assembled a catalogue of the X-ray properties of stars hosting giant planets and studied a possible desert we identified in the X-ray luminosity – semi-major axis plane (L_X-a) ∼ (10²⁸ erg s^-1 – 0.2 au). While this desert could be qualitatively explained as a consequence of disc dispersal via X-ray photoevaporation, which stops giant planet migration at a given place in the disc and for a given range of X-ray luminosities, unfortunately its statistical significance could not be proved with the data set available in 2019. Our statistical tests showed that unless the size and location of the feature can be known a-priori, a significant increase in observational data points would be required in order to statistically prove the existence of a desert. Further theoretical work by Monsch et al. (2020a,b, to be submitted in early 2020, see below), have attempted to use theoretical models to better constrain the expected morphology of the desert, but identified instead several shortcomings in the current state-of-the-art numerical methods that are relevant not only to this project but to the whole field of planet population synthesis studies. In Monsch et al. (2020b) we  propose improvements and revised recipes for planet migration by the impulse approximation which will be able to enhance the predictive power of 1D calculations, allowing future investigations to provide more realistic population synthesis of planets in evolving protoplanetary discs.