Runaway gas accretion and ALMA observations

We point out that these observations set unique 'live' constraints on the process of gas accretion on to sub-Jovian planets that were not previously available. Accordingly, we use a population synthesis approach in a new way: we build time-resolved models and compare the properties of the synthetic planets with the ALMA data at the same age.

Applying the widely used gas accretion formulae leads to a deficit of sub-Jovian planets and an overabundance of a few Jupiter mass planets compared to observations. We find that gas accretion rate on to planets needs to be suppressed by about an order of magnitude to match the observed planet mass function. This slower gas giant growth predicts that the planet mass should correlate positively with the age of the protoplanetary disc, albeit with a large scatter.