Growing porous grains: a solution to the radial-drift barrier
Abstract
Protoplanetary discs are made of gas and dust orbiting around young stars. Initially submicronic, dust grains can grow by coagulation during collisions until they reach millimetre, then kilometer (planetesimal) and planetary sizes. However, theory indicates that once grains reach a size (between millimetre and meter) for which the planet growth timescale is shorter than the accretion timescale, they drift inwards due to the aerodynamical drag force and are accreted onto the star. This effect goes under the name of “radial-drift barrier”. Several solutions to this problem have been proposed. In this work, we focus on an intrinsic property of grains: porosity. We investigate the effects porosity can have on grain growth and dynamics using an analytical model. Taking only drift into account (no growth), we find that porous grains are slowed down but also tend to be compressed by the gas in the inner parts of the disc. Analysing growth at fixed distance from the star (no drift), we show that porous grains grow faster and more efficiently than compact ones. Combining drift and growth, we demonstrate that porous grains can overcome the radial-drift barrier and keep growing in the inner parts of the disc while compact grains fall into the star.
- Publication:
-
SF2A-2016: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics
- Pub Date:
- December 2016
- Bibcode:
- 2016sf2a.conf..449G
- Keywords:
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- Protoplanetary discs;
- Planets and satellites: formation;
- Star: circumstellar matter;
- Methods: analytical