Constraints on Super-Earth Interiors from Stellar Abundances

Brugger, B.; Mousis, O.; Deleuil, M.; Deschamps, Frédéric

doi:10.3847/1538-4357/aa965a

Cited by 106 publications

(114 citation statements)

References 62 publications

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“…Considering their densities and that their mass are 10 M ⊕ , these planets likely have a rocky core and a substantial atmospheric layer, composed of volatiles. Such a layer is not taken into account in current models of super-Earth interiors (Brugger et al 2017). The modelling of the planets is therefore beyond the scope of this paper and will be the subject of a forthcoming study.…”

Section: Validity Of the Detectionsmentioning

confidence: 99%

“…Mass-radius diagram of small planets with masses up to 22 M ⊕ and radius up to 5 R ⊕ . From top to bottom, the lines denotes different compositions for solid planets in between pure water and pure iron (Brugger et al 2017). We superimposed the known planets (from the NASA Exoplanet Archive, updated on 2019 May 05) in this mass-radius range where the grey-scale depends on the precision on the mass and radius.…”

Section: A Favourable System To Search For Co-orbitalsmentioning

confidence: 99%

“…This is particularly true for internal structure modelling which, beyond the degeneracies inherent to this type of investigation, requires a precise determination of the planetary bulk density (Seager et al Table A.3 is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb. u-strasbg.fr/cgi-bin/qcat?J/A+A/ 2007; Brugger et al 2017). This is also true for atmospheric studies which rely on mass measurements to derive the scale height, which is an essential parameter to interpret observations in transmission spectroscopy (e.g.…”

Section: Introductionmentioning

confidence: 98%

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Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

Lopez

Barros

Santerne

et al. 2019

A&A

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The detection of low-mass transiting exoplanets in multiple systems brings new constraints to planetary formation and evolution processes and challenges the current planet formation theories. Nevertheless, only a mere fraction of the small planets detected by Kepler and K2 have precise mass measurements, which are mandatory to constrain their composition. We aim to characterise the planets that orbit the relatively bright star K2-138. This system is dynamically particular as it presents the longest chain known to date of planets close to the 3:2 resonance. We obtained 215 HARPS spectra from which we derived the radial-velocity variations of K2-138. Via a joint Bayesian analysis of both the K2 photometry and HARPS radial-velocities (RVs), we constrained the parameters of the six planets in orbit. The masses of the four inner planets, from b to e, are 3.1, 6.3, 7.9, and 13.0 M ⊕ with a precision of 34%, 20%, 18%, and 15%, respectively. The bulk densities are 4.9, 2.8, 3.2, and 1.8 g cm −3 , ranging from Earth to Neptune-like values. For planets f and g, we report upper limits. Finally, we predict transit timing variations of the order two to six minutes from the masses derived. Given its peculiar dynamics, K2-138 is an ideal target for transit timing variation (TTV) measurements from space with the upcoming CHaracterizing ExOPlanet Satellite (CHEOPS) to study this highly-packed system and compare TTV and RV masses.

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Section: Validity Of the Detectionsmentioning

confidence: 99%

Section: A Favourable System To Search For Co-orbitalsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

Lopez

Barros

Santerne

et al. 2019

A&A

Self Cite

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“…1, bottom 25 , which can be considered as a proxy for the protoplanetary disc composition. According to these ratios, the ironrich composition of Kepler-107c cannot be primordial 73 . Moreover, Fe/Ni-metal and Mg-silicates have similar volatility and condensation temperatures 74 in nebula; therefore, it is rather difficult to alter these ratios in the planet composition through merely temperature effects in the protoplanetary disc, and in particular for the Kepler-107 system where the outer planet (c) is denser than the inner one (b).…”

Section: Transit Fitting and Planetary Parametersmentioning

confidence: 99%

A giant impact as the likely origin of different twins in the Kepler-107 exoplanet system

et al. 2019

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Measures of exoplanet bulk densities indicate that small exoplanets with radius less than 3 Earth radii ( R ⊕ ) range from low-density sub-Neptunes containing volatile elements 1 to higher density rocky planets with Earth-like 2 or iron-rich 3 (Mercury-like) compositions. Such astonishing diversity in observed small exoplanet compositions may be the product of different initial conditions of the planet-formation process and/or different evolutionary paths that altered the planetary properties after formation 4 . Planet evolution may be especially affected by either photoevaporative mass loss induced by high stellar X-ray and extreme ultraviolet (XUV) flux 5 or giant impacts 6 . Although there is some evidence for the former 7,8 , there are no unambiguous findings so far about the occurrence of giant impacts in an exoplanet system. Here, we characterize the two innermost planets of the compact and nearresonant system Kepler-107 (ref. 9 ). We show that they have nearly identical radii (about 1.5-1.6 R ⊕ ), but the outer planet Kepler-107c is more than twice as dense (about 12.6 g cm -3 ) as the innermost Kepler-107b (about 5.3 g cm -3 ). In consequence, Kepler-107c must have a larger iron core fraction than Kepler-107b. This imbalance cannot be explained by the stellar XUV irradiation, which would conversely make the more-irradiated and less-massive planet Kepler-107b denser than Kepler-107c. Instead, the dissimilar densities are consistent with a giant impact event on Kepler-107c that would have stripped off part of its silicate mantle. This hypothesis is supported by theoretical predictions from collisional mantle stripping 10 , which match the mass and radius of Kepler-107c.

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“…A common approach to the interior characterization of exoplanets is the use of numerical models to compute interior structures which comply with the measured mass and radius of the planet (e.g., Sotin et al 2007;Valencia et al 2007;Fortney et al 2007;Wagner et al 2011;Zeng & Sasselov 2013;Unterborn & Panero 2019). As this is an inverse problem, it requires the calculation of a large number of interior models to obtain an overview over possible interior structures (Rogers & Seager 2010a;Dorn et al 2017;Brugger et al 2017). If other ob-arXiv:1911.12745v1 [astro-ph.EP] 28 Nov 2019 servables are used in addition to mass and radius, the number of samples needed for an accurate inference of possible interior structures increases drastically, due to the increase in dimensionality (e.g., James et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Machine-learning Inference of the Interior Structure of Low-mass Exoplanets

Baumeister

Padovan

Tosi

et al. 2020

ApJ

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We explore the application of machine learning based on mixture density neural networks (MDNs) to the interior characterization of low-mass exoplanets up to 25 Earth masses constrained by mass, radius, and fluid Love number k 2 . We create a dataset of 900 000 synthetic planets, consisting of an iron-rich core, a silicate mantle, a high-pressure ice shell, and a gaseous H/He envelope, to train a MDN using planetary mass and radius as inputs to the network. For this layered structure, we show that the MDN is able to infer the distribution of possible thicknesses of each planetary layer from mass and radius of the planet. This approach obviates the time-consuming task of calculating such distributions with a dedicated set of forward models for each individual planet. While gas-rich planets may be characterized by compositional gradients rather than distinct layers, the method presented here can be easily extended to any interior structure model. The fluid Love number k 2 bears constraints on the mass distribution in the planets' interior and will be measured for an increasing number of exoplanets in the future. Adding k 2 as an input to the MDN significantly decreases the degeneracy of the possible interior structures. In an open repository we provide the trained MDN to be used through a Python Notebook.

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Constraints on Super-Earth Interiors from Stellar Abundances

Cited by 106 publications

References 62 publications

Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

A giant impact as the likely origin of different twins in the Kepler-107 exoplanet system

Machine-learning Inference of the Interior Structure of Low-mass Exoplanets

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