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Enhanced constraints on the interior composition and structure of terrestrial exoplanets

Wang, H S; Liu, F LU ; Ireland, T R; Brasser, R; Yong, D and Lineweaver, C H (2019) In Monthly Notices of the Royal Astronomical Society 482(2). p.2222-2233
Abstract
Exoplanet interior modelling usually makes the assumption that the elemental abundances of a planet are identical to those of its host star. Host stellar abundances are good proxies of planetary abundances, but only for refractory elements. This is particularly true for terrestrial planets, as evidenced by the relative differences in bulk chemical composition between the Sun and the Earth and other inner Solar system bodies. The elemental abundances of a planet host star must therefore be devolatilized in order to correctly represent the bulk chemical composition of its terrestrial planets. Furthermore, nickel and light elements make an important contribution alongside iron to the core of terrestrial planets. We therefore adopt an extended... (More)
Exoplanet interior modelling usually makes the assumption that the elemental abundances of a planet are identical to those of its host star. Host stellar abundances are good proxies of planetary abundances, but only for refractory elements. This is particularly true for terrestrial planets, as evidenced by the relative differences in bulk chemical composition between the Sun and the Earth and other inner Solar system bodies. The elemental abundances of a planet host star must therefore be devolatilized in order to correctly represent the bulk chemical composition of its terrestrial planets. Furthermore, nickel and light elements make an important contribution alongside iron to the core of terrestrial planets. We therefore adopt an extended chemical network of the core, constrained by an Fe/Ni ratio of 18 ± 4 (by number). By applying these constraints to the Sun, our modelling reproduces the composition of the mantle and core, as well as the core mass fraction of the Earth. We also apply our modelling to four exoplanet host stars with precisely measured elemental abundances: Kepler-10, Kepler-20, Kepler-21, and Kepler-100. If these stars would also host terrestrial planets in their habitable zone, we find that such planets orbiting Kepler-21 would be the most Earth-like, while those orbiting Kepler-10 would be the least. To assess the similarity of a rocky exoplanet to the Earth in terms of interior composition and structure, high-precision host stellar abundances are critical. Our modelling implies that abundance uncertainties should be better than ∼0.04 dex for such an assessment to be made.

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author
organization
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type
Contribution to journal
publication status
published
subject
in
Monthly Notices of the Royal Astronomical Society
volume
482
issue
2
pages
2222 - 2233
publisher
Oxford University Press (OUP)
ISSN
0035-8711
DOI
10.1093/mnras/sty2749
language
English
LU publication?
yes
id
811dc113-7c2e-4796-b2f8-ad3cc8dbf1d1
date added to LUP
2018-11-07 13:09:45
date last changed
2019-02-11 04:00:25
@article{811dc113-7c2e-4796-b2f8-ad3cc8dbf1d1,
  abstract     = {Exoplanet interior modelling usually makes the assumption that the elemental abundances of a planet are identical to those of its host star. Host stellar abundances are good proxies of planetary abundances, but only for refractory elements. This is particularly true for terrestrial planets, as evidenced by the relative differences in bulk chemical composition between the Sun and the Earth and other inner Solar system bodies. The elemental abundances of a planet host star must therefore be devolatilized in order to correctly represent the bulk chemical composition of its terrestrial planets. Furthermore, nickel and light elements make an important contribution alongside iron to the core of terrestrial planets. We therefore adopt an extended chemical network of the core, constrained by an Fe/Ni ratio of 18 ± 4 (by number). By applying these constraints to the Sun, our modelling reproduces the composition of the mantle and core, as well as the core mass fraction of the Earth. We also apply our modelling to four exoplanet host stars with precisely measured elemental abundances: Kepler-10, Kepler-20, Kepler-21, and Kepler-100. If these stars would also host terrestrial planets in their habitable zone, we find that such planets orbiting Kepler-21 would be the most Earth-like, while those orbiting Kepler-10 would be the least. To assess the similarity of a rocky exoplanet to the Earth in terms of interior composition and structure, high-precision host stellar abundances are critical. Our modelling implies that abundance uncertainties should be better than ∼0.04 dex for such an assessment to be made.<br/><br/> },
  author       = {Wang, H S and Liu, F and Ireland, T R and Brasser, R and Yong, D and Lineweaver, C H},
  issn         = {0035-8711},
  language     = {eng},
  number       = {2},
  pages        = {2222--2233},
  publisher    = {Oxford University Press (OUP)},
  series       = {Monthly Notices of the Royal Astronomical Society},
  title        = {Enhanced constraints on the interior composition and structure of terrestrial exoplanets},
  url          = {http://dx.doi.org/10.1093/mnras/sty2749},
  volume       = {482},
  year         = {2019},
}