THE HEAVY-ELEMENT MASSES OF EXTRASOLAR GIANT PLANETS, REVEALED

By N. Miller, Jon Fortney. 2011

170 citations recorded by the source corpus.

We investigate a population of transiting planets that receive relatively modest stellar insolation, indicating equilibrium temperatures <1000 K, and for which the heating mechanism that inflates hot Jupiters does not appear to be significantly active. We use structural evolution models to infer the amount of heavy elements within each of these planets. There is a correlation between the stellar metallicity and the mass of heavy elements in its transiting planet(s). It appears that all giant planets possess a minimum of ∼10–15 Earth masses of heavy elements, with planets around metal-rich stars having larger heavy-element masses. There is also an inverse relationship between the mass of the planet and the metal enrichment (Zpl/Zstar), which appears to have little dependency on the metallicity of the star. Saturn- and Jupiter-like enrichments above solar composition are a hallmark of all the gas giants in the sample, even planets of several Jupiter masses. These relationships provide an important constraint on planet formation and suggest large amounts of heavy elements within planetary H/He envelopes. We suggest that the observed correlation can soon also be applied to inflated planets, such that the interior heavy-element abundance of these planets could be estimated, yielding better constraints on their interior energy sources. We point to future directions for planetary population synthesis models and suggest future correlations. This appears to be the first evidence that extrasolar giant planets, as a class, are enhanced in heavy elements.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/6f0c1b0b4ef56cd95382eb94a4981a1132f2a621

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Citations in the corpus

THE MASS OF KOI-94d AND A RELATION FOR PLANET RADIUS, MASS, AND INCIDENT FLUX (2013, methodology): “Including uncertainties in the system age, planet mass, planet radius, orbital semi-major axis, and heavy element distribution within the planet (see Miller & Fortney 2011) we estimate that 18±6 M⊕ of heavy elements are contained within the planet.”
KEPLER-18b, c, AND d: A SYSTEM OF THREE PLANETS CONFIRMED BY TRANSIT TIMING VARIATIONS, LIGHT CURVE VALIDATION, WARM-SPITZER PHOTOMETRY, AND RADIAL VELOCITY MEASUREMENTS (2011, methodology): “As in Miller & Fortney (2011), all relevant uncertainties are accounted for.”
Accurate Empirical Radii and Masses of Planets and Their Host Stars with Gaia Parallaxes (2016, background): “Indeed, evidence for a correlation between the inferred core mass of warm Jupiters and the heavy element composition of the host star lends credence to the idea that 1 most, if not all, close-in giant planets form via core accretion (Miller & Fortney 2011).”
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).”
THE MASS–METALLICITY RELATION FOR GIANT PLANETS (2015, background): “Planets that receive an incident flux below around 2×108 erg s−1 cm−2 (Teq1000 K) appear to be non-inflated (Demory & Seager 2011; Miller & Fortney 2011), obviating the need for assumptions about that effect.”
LACK OF INFLATED RADII FOR KEPLER GIANT PLANET CANDIDATES RECEIVING MODEST STELLAR IRRADIATION (2011, background): “Although the giant planet radius trend was hinted with published giant planets alone (Miller & Fortney 2011, see also Fig.”
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).”
Characterization of exoplanets from their formation - II. The planetary mass-radius relationship (2012, background): “An already known example is the correlation between stellar [Fe/H] and planetary heavy element content (Guillot et al. 2006; Burrows et al. 2007; Miller & Fortney 2011).”
UNDERSTANDING THE MASS–RADIUS RELATION FOR SUB-NEPTUNES: RADIUS AS A PROXY FOR COMPOSITION (2013, background): “It is unclear why there do not appear to be any super-inflated hot Jupiters below∼ 100M⊕, it is possible that such planets would be unstable to photo-evaporation or Roche-lobe overflow (Jackson et al. 2010) or have a high mass fraction of heavy elements (Miller & Fortney 2011).”
MASSES, RADII, AND CLOUD PROPERTIES OF THE HR 8799 PLANETS (2012, background): “The available data on exoplanet masses and radii suggest that lower mass planets are more heavily enriched in heavy elements than higher mass planets (Miller & Fortney 2011).”
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 IMPRINT OF EXOPLANET FORMATION HISTORY ON OBSERVABLE PRESENT-DAY SPECTRA OF HOT JUPITERS (2016, background): “But the fact that both the planets analyzed by Miller & Fortney (2011); Thorngren et al. (2015) (a =0.03-1 AU, Teq .1000 K) and the solar system planets (a ≈5-30 AU) follow the same trend, makes it appear unlikely -even though in principle not excluded- that the hot Jupiters at a ∼ 0.04 AU do not…”
THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA (2015, background): “…between the bulk metal content and the yet-to-be definitively determined “inflation” mechanisms (e.g., Batygin, Stevenson, & Bodenheimer 2011; Miller & Fortney 2011; Thorngren, Fortney, & Lopez 2015), and it is not yet clear how the bulk metal content partitions itself between the core and…”
CHARACTERIZING THE COOL KOIs. II. THE M DWARF KOI-254 AND ITS HOT JUPITER (2011, background): “This is a remarkably large core mass (heavy element content) and conforms well with the observed correlation between planetary heavy element content and host star metallicity (Burrows et al. 2007; Torres et al. 2008; Miller & Fortney 2011).”