Abstract

It is known that ~20% of nearby stars host planetesimal belts orbiting 10s of au from the star. For a growing number CO gas has been detected coincident with the planetesimal belts showing that their planetesimals have a similar composition to Solar System comets. It is expected that some of these planetesimals may be perturbed into the inner regions of the system where they may collide with any planets residing there. The hot dust seen in several systems may be evidence of such comet-like dynamics, and in one system this picture is reinforced by the detection of CO close to the CO2 sublimation radius. This seminar will consider the effect of collisions with such an exocomet population on the atmospheres of inner planets. These atmospheres can be stripped in collisions, but can also be enhanced by the delivery of volatiles, in a way that can be quantified from simulations of impacts. It will be shown that whether an atmosphere grows or depletes can be inferred from the planet’s mass and semimajor axis (for given assumptions about the cometary impactors). While application to the Solar System terrestrial planets highlights the sensitivity of conclusions to the model assumptions (e.g., since the Earth lies close to the growth/depletion boundary), application to extrasolar planetary systems shows that broad trends are more robust, such as the depletion of the atmospheres of close-in exoplanets like those of TRAPPIST -1, and the growth of those at larger separation.