Institute of Astronomy

Formation of planetesimals in evolving accretion discs

SpeakerTalk DateTalk Series
Bertram Bitsch31 July 2014Across HR 2014 Talks


Planetesimals are the seeds in the core accretion model to form terrestrial planets and the cores of gas giants. The formation of planetesimals can be triggered by the streaming instability (Johansen & Youdin, 2007). This process depends on the relation between the mean gas flow and a pure Keplerian orbit, which strongly depends on the underlying disc structure. In the simple power-law assumptions made in the Minimum-Mass-Solar-Nebula (MMSN), it is much harder to form planetesimals further away from the star. Recent simulations of accretion discs which include stellar heating and radiative cooling have shown that accretion discs are not uniform power laws, but show some bumps and dips (Bitsch et al, 2013a, 2014). These changes in the disc structure then alter the location of the regions in the disc where planetesimals can be formed by the streaming instability. We present studies of accretion discs with different accretion rates and their influence on the formation of planetesimals. We also investigate the influence of viscosity transitions in the disc and their role in the formation of planetesimals. Additionally we present a more accurate model of the structure of accretion discs that allows for detailed predictions for the formation of planetesimals, pebble accretion and the migration of planets, than the MMSN model.