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

The location of giant planets may play an important role on habitability of the terrestrial planets in the same system. As an example, giant planets are thought to affect the delivery of volatiles to terrestrial planets as well as stopping the infux of pebbles from the outer disc, possibly preventing the early formation of terrestrial planets.

In the first funding period of the SPP1992 we explored the 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. 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. This feature 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., 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. We propose improvements and revised recipes for planet migration by the impulse approximation to enhance the predictive power of 1D calculations, allowing future investigations to provide more realistic population synthesis of planets in evolving protoplanetary discs.

In this project we plan to capitalise on the results obtained, using an enhanced dataset, which will include data from TESS and the e-Rosita mission and our improved numerical methods (Monsch et al. 2020a,b) combined with the state-of-the-art population synthesis code from the Bern group (e.g. Mordasini et al. 2009, 2012) to prove conclusively the existence of a desert of warm giants in the (LX − a) plane. The significance of this potential result is not to be underestimated. If we can prove that the feature identified by Monsch et al. (2019) is indeed real, this would mean that, statistically, the location of giants in the system is set during the time of planet formation and migration inside the protoplanetary disc and that successive dynamical interaction after disc dispersal have a smaller effect on the final architecture of a system and thus on its habitability. Furthermore, this result would prove once and for all that X-rays from the central star drive disc dispersal and significantly affect its planetary progeny.