Formation of secondary atmospheres on terrestrial planets by late disk accretion. (arXiv:2004.02496v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kral_Q/0/1/0/all/0/1">Quentin Kral</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Davoult_J/0/1/0/all/0/1">Jeanne Davoult</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Charnay_B/0/1/0/all/0/1">Benjamin Charnay</a>
Recently, gas disks have been discovered around main sequence stars well
beyond the usual protoplanetary disk lifetimes (i.e., > 10 Myrs), when planets
have already formed. These gas disks, mainly composed of CO, carbon, and oxygen
seem to be ubiquitous in systems with planetesimal belts (similar to our Kuiper
belt), and can last for hundreds of millions of years. Planets orbiting in
these gas disks will accrete a large quantity of gas that will transform their
primordial atmospheres into new secondary atmospheres with compositions similar
to that of the parent gas disk. Here, we quantify how large a secondary
atmosphere can be created for a variety of observed gas disks and for a wide
range of planet types. We find that gas accretion in this late phase is very
significant and an Earth’s atmospheric mass of gas is readily accreted on
terrestrial planets in very tenuous gas disks. In slightly more massive disks,
we show that massive CO atmospheres can be accreted, forming planets with up to
sub-Neptune-like pressures. Our new results demonstrate that new secondary
atmospheres with high metallicities and high C/O ratios will be created in
these late gas disks, resetting their primordial compositions inherited from
the protoplanetary disk phase, and providing a new birth to planets that lost
their atmosphere to photoevaporation or giant impacts. We therefore propose a
new paradigm for the formation of atmospheres on low-mass planets, which can be
tested with future observations (JWST, ELT, ARIEL). We also show that this late
accretion would show a very clear signature in Sub-Neptunes or cold
exo-Jupiters. Finally, we find that accretion creates cavities in late gas
disks, which could be used as a new planet detection method, for low mass
planets a few au to a few tens of au from their host stars.
Recently, gas disks have been discovered around main sequence stars well
beyond the usual protoplanetary disk lifetimes (i.e., > 10 Myrs), when planets
have already formed. These gas disks, mainly composed of CO, carbon, and oxygen
seem to be ubiquitous in systems with planetesimal belts (similar to our Kuiper
belt), and can last for hundreds of millions of years. Planets orbiting in
these gas disks will accrete a large quantity of gas that will transform their
primordial atmospheres into new secondary atmospheres with compositions similar
to that of the parent gas disk. Here, we quantify how large a secondary
atmosphere can be created for a variety of observed gas disks and for a wide
range of planet types. We find that gas accretion in this late phase is very
significant and an Earth’s atmospheric mass of gas is readily accreted on
terrestrial planets in very tenuous gas disks. In slightly more massive disks,
we show that massive CO atmospheres can be accreted, forming planets with up to
sub-Neptune-like pressures. Our new results demonstrate that new secondary
atmospheres with high metallicities and high C/O ratios will be created in
these late gas disks, resetting their primordial compositions inherited from
the protoplanetary disk phase, and providing a new birth to planets that lost
their atmosphere to photoevaporation or giant impacts. We therefore propose a
new paradigm for the formation of atmospheres on low-mass planets, which can be
tested with future observations (JWST, ELT, ARIEL). We also show that this late
accretion would show a very clear signature in Sub-Neptunes or cold
exo-Jupiters. Finally, we find that accretion creates cavities in late gas
disks, which could be used as a new planet detection method, for low mass
planets a few au to a few tens of au from their host stars.
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