1 research outputs found
Metallicity effect and planet mass function in pebble-based planet formation models
One of the main scenarios of planet formation is the core accretion model
where a massive core forms first and then accretes a gaseous envelope. This
core forms by accreting solids, either planetesimals, or pebbles. A key
constraint in this model is that the accretion of gas must proceed before the
dissipation of the gas disc. Classical planetesimal accretion scenario predicts
that the time needed to form a giant planets core is much longer than the time
needed to dissipate the disc. This difficulty led to the development of another
accretion scenario, in which cores grow by accretion of pebbles, which are much
smaller and thus more easily accreted, leading to a more rapid formation. The
aim of this paper is to compare our updated pebble-based planet formation model
with observations, in particular the well studied metallicity effect. We adopt
the Bitsch et al. 2015a disc model and the Bitsch et al. 2015b pebble model and
use a population synthesis approach to compare the formed planets with
observations. We find that keeping the same parameters as in Bitsch et al.
2015b leads to no planet growth due to a computation mistake in the pebble flux
(Bitsch et al. 2017). Indeed a large fraction of the heavy elements should be
put into pebbles (Zpeb/Ztot = 0.9) in order to form massive planets using this
approach. The resulting mass functions show a huge amount of giants and a lack
of Neptune mass planets, which are abundant according to observations. To
overcome this issue we include the computation of the internal structure for
the planetary atmosphere to our model. This leads to the formation of Neptune
mass planets but no observable giants. Reducing the opacity of the planetary
envelope finally matches observations better. We conclude that modeling the
internal structure for the planetary atmosphere is necessary to reproduce
observations.Comment: 13 pages, 22 figure