Pebbles versus Planetesimals: The case of Trappist-1. (arXiv:1908.04166v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Coleman_G/0/1/0/all/0/1">Gavin A. L. Coleman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Leleu_A/0/1/0/all/0/1">Adrien Leleu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alibert_Y/0/1/0/all/0/1">Yann Alibert</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Benz_W/0/1/0/all/0/1">Willy Benz</a>
We present a study on the formation of planetary systems around low mass
stars similar to Trappist-1, through the accretion of either planetesimals or
pebbles. The aim is to determine if the currently observed systems around low
mass stars favour one scenario over the other. We ran numerous N-body
simulations, coupled to a thermally evolving viscous disc model, including
prescriptions for planet migration and photoevaporation. We examine the
differences between the pebble and planetesimal accretion scenarios, but also
look at the influences of disc mass, planetesimal size, and the percentage of
solids locked up within pebbles. When comparing the resulting planetary systems
to Trappist-1, we find that a wide range of initial conditions for both
accretion scenarios can form planetary systems similar to Trappist-1, in terms
of planet mass, periods, and resonant configurations. Typically these planets
formed exterior to the water iceline and migrated in resonant convoys to close
to the central star. When comparing the planetary systems formed from pebbles
to those formed from planetesimals, we find a large number of similarities,
including average planet masses, eccentricities, inclinations and period
ratios. One major difference was that of the water content of the planets. When
including the effects of ablation and full recycling of the planets envelope
with the disc, planets formed from pebbles were extremely dry, whilst those
formed from planetesimals were extremely wet. If the water content is not fully
recycled and instead falls to the planets core, or if ablation of the water is
neglected, then the planets formed from pebbles are extremely wet, similar to
those formed from planetesimals. Should the water content of the Trappist-1
planets be determined accurately, this could point to a preferred formation
pathway for planetary systems, or to specific physics that may be at play.
We present a study on the formation of planetary systems around low mass
stars similar to Trappist-1, through the accretion of either planetesimals or
pebbles. The aim is to determine if the currently observed systems around low
mass stars favour one scenario over the other. We ran numerous N-body
simulations, coupled to a thermally evolving viscous disc model, including
prescriptions for planet migration and photoevaporation. We examine the
differences between the pebble and planetesimal accretion scenarios, but also
look at the influences of disc mass, planetesimal size, and the percentage of
solids locked up within pebbles. When comparing the resulting planetary systems
to Trappist-1, we find that a wide range of initial conditions for both
accretion scenarios can form planetary systems similar to Trappist-1, in terms
of planet mass, periods, and resonant configurations. Typically these planets
formed exterior to the water iceline and migrated in resonant convoys to close
to the central star. When comparing the planetary systems formed from pebbles
to those formed from planetesimals, we find a large number of similarities,
including average planet masses, eccentricities, inclinations and period
ratios. One major difference was that of the water content of the planets. When
including the effects of ablation and full recycling of the planets envelope
with the disc, planets formed from pebbles were extremely dry, whilst those
formed from planetesimals were extremely wet. If the water content is not fully
recycled and instead falls to the planets core, or if ablation of the water is
neglected, then the planets formed from pebbles are extremely wet, similar to
those formed from planetesimals. Should the water content of the Trappist-1
planets be determined accurately, this could point to a preferred formation
pathway for planetary systems, or to specific physics that may be at play.
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