A correlation between the heavy element content of transiting extrasolar planets and the metallicity of their parent stars

By T. Guillot, Nuno C. Santos, F. Pont, N. Iro, C. Melo, I. Ribas. 2006

232 citations recorded by the source corpus.

Context. Nine extrasolar planets with masses between 110 and 430M⊕ are known to transit their star. The knowledge of their masses and radii allows an estimate of their composition, but uncertainties on equations of state, opacities and possible missing energy sources imply that only inaccurate constraints can be derived when considering each planet separately. Aims. We seek to better understand the composition of transiting extrasolar planets by considering them as an ensemble, and by comparing the obtained planetary properties to that of the parent stars. Methods. We use evolution models and constraints on the stellar ages to derive the mass of heavy elements present in the planets. Possible additional energy sources like tidal dissipation due to an i nclined orbit or to downward kinetic energy transport are considered. Results. We show that the nine transiting planets discovered so far belong to a quite homogeneous ensemble that is characterized by a mass of heavy elements that is a relatively steep function of the s tellar metallicity, from less than 20 earth masses of heavy elements around solar composition stars, to up to∼ 100 M⊕ for three times the solar metallicity (the precise values be ing model-dependant). The correlation is still to be ascertained however. Statistical tests imply a worst-ca se 1/3 probability of a false positive. Conclusions. Together with the observed lack of giant planets in close orbits around metal-poor stars, these results appear to imply t hat heavy elements play a key role in the formation of close-in giant planets. The large masses of heavy elements inferred for planets orbiting metal rich stars was not anticipated by planet formation models and shows the need for alternative theories including migration and subsequent collection of planetesimals.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/c1cacfaf12ab33218652a5e939d605f0e0ddc895

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In Astronomy and Astrophysics

1. Jon Fortney
2. N. Madhusudhan
3. C. Mordasini
4. Sara Seager
5. M. Marley
6. D. Charbonneau
7. A. Showman
8. H. Knutson

In Nuclear and High Energy Physics

1. M. Mayor
2. D. Charbonneau
3. S. Udry
4. Jon Fortney
5. Sérgio F. Sousa
6. Nuno C. Santos
7. H. Knutson
8. G. Israelian

Citations in the corpus

• A diagram to determine the evaporation status of extrasolar planets (2006, background): “…of the planet interior at several bars pressure not affected by the evaporation operating much higher in the atmosphere; this is confirmed by the absence of a correlation of the observed radii of transiting planets with age and EUV flux received during the planets’ lifetime (Guillot et al. 2006).”
• Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity (2008, background): “…different eccentricity distributions for the radial velocity planets above and below 4MJ. Additionally, transiting planet mass and radius determinations allow forcalculations of bulk planet density, which shed light on the intr al abundance of heavy elements (Guillot et al. 2006; Fortney etal.”
• On the radiative equilibrium of irradiated planetary atmospheres (2010, background): “The cross corresponds to the outer boundary condition used by Guillot et al. (2006) and Guillot (2008) to calculate the evolution of the planet.”
• Two Classes of Hot Jupiters (2007, background): “Here is defined as a fraction of the irradiance for each planet, in the spirit of Guillot et al. (2006).”
• Improving Stellar and Planetary Parameters of Transiting Planet Systems: The Case of TrES-2 (2007, background): “The smaller than expected radii of other transiting planets (e.g., HD 149026b) can instead be explained by the presence of dense rocky cores, and a correlation has been proposed between inner core masses and host star metallicities (Guillot et al. 2006; Burrows et al. 2007).”
• SPECTRAL AND PHOTOMETRIC DIAGNOSTICS OF GIANT PLANET FORMATION SCENARIOS (2011, background): “For a given bulk entropy, it causes an object to have a smaller radius (Burrows et al. 2000; Guillot et al. 2006; Leconte et al. 2009; Ibgui et al. 2010).”
• Using Stellar Limb-Darkening to Refine the Properties of HD 209458b (2006, background): “If the second explanation is correct, most hot Jupiters would need significantly larger solid cores than currently predicted by current formation models (Guillot et al. 2006).”
• Rapid growth of gas-giant cores by pebble accretion (2012, background): “…2004; Fischer & Valenti 2005) is also accompanied by a correlation between stellar metallicity and the amount of heavy elements present in the exoplanetary interior (Guillot et al. 2006; Miller & Fortney 2011), for objects in the gas giant mass range between about 0.3 and 10 Jupiter masses (MJ).”
• SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period (2015, background): “A correlation between the core mass and the stellar metalicity has been proposed earlier on the basis of a comparison between theoretical interior models and observations of transiting planets (Guillot et al. 2006; Burrows et al. 2007; Miller & Fortney 2011; Moutou et al. 2013).”
• Predicting low-frequency radio fluxes of known extrasolar planets (2007, background): “Different explanations have been put forward for the anomalously large radius of this planet, but so far no conclusive answer to this question has been found (see e.g. Guillot et al., 2006, and references therein).”
• Possible Solutions to the Radius Anomalies of Transiting Giant Planets (2006, result): “Based on their preliminary analysis, Guillot et al. (2006) suggest a similar correlation.”
• THE HEAVY-ELEMENT MASSES OF EXTRASOLAR GIANT PLANETS, REVEALED (2011, background): “For the over-inflated planets it is possible to find a relation between the heavy elements in the planets and the metallicity of the stars by making an assumption about the relationship between the incident stellar radiation and the unknown power input into the planet (Guillot et al. 2006).”
• Forming the cores of giant planets from the radial pebble flux in protoplanetary discs (2014, background): “Models of giant exoplanets in short orbits show similar core masses, on the order of 10 Earth masses (ME) or larger (Guillot et al. 2006; Miller & Fortney 2011; Moutou et al. 2013).”
• THE MASS–METALLICITY RELATION FOR GIANT PLANETS (2015, methodology): “Still, work has been done to use models to address a the star–planet composition connection, using plausible assumptions about the effect, as a heat source (Guillot et al. 2006) or as a slowed-cooling effect (Burrows et al. 2007).”
• Transits and Occultations (2010, background): “There is also a positive correlation between the metallicity of the host star and the inferred “core mass” of the planet (Guillot et al. 2006), by which is meant the mass of heavy elements required in models of the planetary interior that agree with the observed mass and radius.”
• Extrasolar planet population synthesis - II. Statistical comparison with observations (2009, background): “Indeed, as shown by Guillot et al. (2006), and confirmed by Burrows et al. (2007) and Guillot (2008), internal structure models indicate that there is a positive correlation between the total amount of heavy elements in a planet MZ,tot and the host star metallicity, provided that some ‘missing…”