Building Rocky Planets in the Inner Disc: From Dust to Planetesimals

“Kepler planets” – Earth to few-Earth sized planets, orbiting very close to their parent stars – are ubiquitous around both sun-like stars and M dwarfs, and appear to be a major outcome of the planet formation process. However, no concrete theory for their formation exists. To quantitatively understand how these small, close-in planets are forged from the discs of gas and dust girdling young stars, we must undertake a detailed investigation of the co-evolution of gas and dust in the inner regions of these discs, close to the star. To this end, we have already developed the most sophisticated numerical model to date of the steady-state structure of gas in the inner disc, including the effects of dust grains on the opacity, viscosity and chemistry. Building upon this, we propose to undertake time-dependent numerical simulations of the gas+dust behaviour in the inner disc, including 2D dust dynamics, the feedback of the latter on the gas dynamics, and grain growth and fragmentation. No such detailed simulations of the inner disc have ever been performed before. We will use the new state-of-the-art code cuDisc, developed in-house specifically to model the evolution of dusty discs, for this work. Our results will elucidate, for the first time, the critical initial stage of Kepler planet formation: how, where and when dust grains coalesce into planetesimals (10-100 km sized bodies; the building blocks of planets), in the inner disc region. This in turn will have crucial population-level implications for the compositional and atmospheric properties of Kepler planets, which can be validated against observations by new and upcoming facilities (e.g., JWST, ARIEL, E-ELT), and will also be invaluable for interpreting such observations.