Speaker
Description
Exoplanetary demographic statistics shows that super-Earths are the most
abundant exoplanets, orbiting approximately every other solar-like star. In our own solar system, however, the inner terrestrial planets did not grow beyond Earth in mass. A possible explanation could be provided by the presence of gas giants in our own system, that might have influenced the growth of the inner terrestrial planets. In this project we address this hypothesis, by studying the so-called “pebble filtering” mechanism. During their formation, giant planets accrete part of the pebble disc mass budget, preventing a potentially significant amount of pebbles from drifting inwards and feeding the inner disc region. If this mechanism is very efficient, it can halt planet formation in the inner disc. We perform a parameter study based on pebble accretion simulations, where we assume pebble sizes limited by drift and fragmentation. The initial planetary seeds are taken from the top of the streaming instability and the disc temperature profile is set both by irradiation and viscous heating. We show that one of the key uncertainty is the degree of viscous heating in the inner disc, which regulates the pebble accretion efficiency. In systems with gas-giant formation the role of mutual pebble filtering is generally limited, unless it is paired with some other mechanism that already delays the inner embryo’s growth, such as strong viscous heating of the disc or the presence of an iceline that significantly reduces the available inward-drifting material. This latter point appears to be consistent with the fact that no strong suppression is seen in the occurrence rate of super-Earths in systems with known gas giants in wider orbits. We conclude that the diversity in exoplanetary systems may be due to complex, and as of yet poorly understood, disc accretion physics inside the water ice line. I will also present preliminary results on population synthesis focused on exoplanet formation around the iceline, a population observable through microlensing techniques with the soon-to-be-launched Roman space telescope.
