Influence of sub- and super-solar metallicities on the compositions of solid planetary building blocks. (arXiv:1911.09725v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bitsch_B/0/1/0/all/0/1">Bertram Bitsch</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Battistini_C/0/1/0/all/0/1">Chiara Battistini</a>
The composition of the protoplanetary disc is linked to the composition of
the host star, where a higher overall metallicity of the host star provides
more building blocks for planets. However, most planet formation simulations
only link the stellar iron abundance [Fe/H] to planet formation and [Fe/H] in
itself is used as a proxy to scale all elements. But large surveys of stellar
abundances show that this is not true. We use here stellar abundances from the
GALAH surveys to determine the average detailed abundances of Fe, Si, Mg, O,
and C for a broad range of [Fe/H] spanning from -0.4 to +0.4. Using an
equilibrium chemical model that features the most important rock forming
molecules as well as volatile contributions of H$_2$O, CO$_2$, CH$_4$ and CO,
we calculate the chemical composition of solid planetary building blocks. Solid
building blocks that are formed entirely interior to the water ice line
(T>150K) only show an increase in Mg$_2$SiO$_4$ and a decrease in MgSiO$_3$ for
increasing host star metallicity, related to the increase of Mg/Si for higher
[Fe/H]. Solid planetary building blocks forming exterior to the water ice line
(T<150K) show dramatic changes in their composition. The water ice content
decreases from around $sim$50% at [Fe/H]=-0.4 to $sim$6% at [Fe/H]=0.4 in
our chemical model. This is mainly caused by the increasing C/O ratio with
increasing [Fe/H], which binds most of the oxygen in gaseous CO and CO$_2$,
resulting in a small water ice fraction. Planet formation simulations coupled
with the chemical model confirm these results by showing that the water ice
content of super-Earths decreases with increasing host star metallicity due to
the increased C/O ratio. This decrease of the water ice fraction has important
consequences for planet formation, planetary composition and the eventual
habitability of planetary systems formed around these high metallicity stars.
The composition of the protoplanetary disc is linked to the composition of
the host star, where a higher overall metallicity of the host star provides
more building blocks for planets. However, most planet formation simulations
only link the stellar iron abundance [Fe/H] to planet formation and [Fe/H] in
itself is used as a proxy to scale all elements. But large surveys of stellar
abundances show that this is not true. We use here stellar abundances from the
GALAH surveys to determine the average detailed abundances of Fe, Si, Mg, O,
and C for a broad range of [Fe/H] spanning from -0.4 to +0.4. Using an
equilibrium chemical model that features the most important rock forming
molecules as well as volatile contributions of H$_2$O, CO$_2$, CH$_4$ and CO,
we calculate the chemical composition of solid planetary building blocks. Solid
building blocks that are formed entirely interior to the water ice line
(T>150K) only show an increase in Mg$_2$SiO$_4$ and a decrease in MgSiO$_3$ for
increasing host star metallicity, related to the increase of Mg/Si for higher
[Fe/H]. Solid planetary building blocks forming exterior to the water ice line
(T<150K) show dramatic changes in their composition. The water ice content
decreases from around $sim$50% at [Fe/H]=-0.4 to $sim$6% at [Fe/H]=0.4 in
our chemical model. This is mainly caused by the increasing C/O ratio with
increasing [Fe/H], which binds most of the oxygen in gaseous CO and CO$_2$,
resulting in a small water ice fraction. Planet formation simulations coupled
with the chemical model confirm these results by showing that the water ice
content of super-Earths decreases with increasing host star metallicity due to
the increased C/O ratio. This decrease of the water ice fraction has important
consequences for planet formation, planetary composition and the eventual
habitability of planetary systems formed around these high metallicity stars.
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