Possible Solutions to the Radius Anomalies of Transiting Giant Planets

By Adam Burrows, I. Hubeny, J. Budaj, W. Hubbard. 2006

329 citations recorded by the source corpus.

We calculate the theoretical evolution of the radii of all 14 of the known transiting extrasolar giant planets (EGPs) for a variety of assumptions concerning atmospheric opacity, dense inner core masses, and possible internal power sources. We incorporate the effects of stellar irradiation and customize such effects for each EGP and star. Looking collectively at the family as a whole, we find that there are in fact two radius anomalies to be explained. Not only are the radii of a subset of the known transiting EGPs larger than expected from previous theory, but many of the other objects are smaller than the default theory would allow. We suggest that the larger EGPs can be explained by invoking enhanced atmospheric opacities that naturally retain internal heat. This explanation might obviate the necessity for an extra internal power source. We explain the smaller radii by the presence in perhaps all the known transiting EGPs of dense cores, such as have been inferred for Saturn and Jupiter. Importantly, we derive a rough correlation between the masses of our "best-fit" cores and the stellar metallicity that seems to buttress the core-accretion model of their formation. Although many caveats and uncertainties remain, the resulting comprehensive theory that incorporates enhanced-opacity atmospheres and dense cores is in reasonable accord with all the current structural data for the known transiting giant planets.

Subfields: Astronomy and Astrophysics, Education, Instrumentation

View Paper: https://www.semanticscholar.org/paper/eec22a30d2644a68d515fd8aa8c17520dd051755

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Citations in the corpus

SPECTRAL AND PHOTOMETRIC DIAGNOSTICS OF GIANT PLANET FORMATION SCENARIOS (2011, background): “However, it also leads to greater atmospheric opacity, which retards the rate at which an object cools and loses its initial entropy (Burrows et al. 2007).”
Homogeneous studies of transiting extrasolar planets – I. Light-curve analyses (2008, background): “This effect has been considered in detail by Burrows et al. (2007), who find that for a highly irradiated low-gravity planet the difference in radius can be up to 5%.”
On the radiative equilibrium of irradiated planetary atmospheres (2010, background): “…∫ ∞ 0 e−Z [ πθ̃(r + ∆z,Z)Z ]1/2 dZ (60) In the limit of an isothermal atmosphere,θ̃(r,Z) = 1, the integral is equal to 1 (the erf function evaluated at infinity) and the expression of the chord optical depth and height difference reduce to the relations proposed by Burrows et al. (2007a).”
Tidal Evolution of Close-in Extrasolar Planets (2007, background): “Such a lag seems reasonable based on the long duration of the influence of heat of formation on the planet’s radius in the modeling by Burrows et al. 2007.”
The Very Low Albedo of an Extrasolar Planet: MOST Space-based Photometry of HD 209458 (2007, background): “Jupiter and Saturn, which receive much less UV flux than HD 209458, contain unidentified species at the level of a few parts per 1010 that decrease the blue and green geometric albedos by a factor of 2 (Karkoshka 1994; Burrows et al. 2007a).”
WASP-121 b: a hot Jupiter close to tidal disruption transiting an active F star (2015, background): “…into the planets from strong winds driven by the large day/night temperature contrasts (Showman & Guillot 2002), enhanced atmospheric opacities (Burrows et al. 2007), reduced heat transport efficiency by layered convection inside the planets (Chabrier & Baraffe 2007), or Ohmic heating from…”
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).”
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).”
Accurate Empirical Radii and Masses of Planets and Their Host Stars with Gaia Parallaxes (2016, background): “Despite many suggested solutions to this “inflated Hot Jupiter” problem (Guillot & Showman 2002; Burrows et al. 2007; Chabrier & Baraffe 2007; Jackson et al. 2009; Arras & Socrates 2010; Batygin et al. 2011), no one explanation has emerged as the leading contender, although empirical trends with…”
Is tidal heating sufficient to explain bloated exoplanets? Consistent calculations accounting for finite initial eccentricity (2010, background): “The existence of objects below the R = Rirrad line is a clear signature of the presence of a dense core and/or of the enrichment of the gaseous envelop (Baraffe et al. 2006; Fortney et al. 2007; Burrows et al. 2007; Baraffe et al. 2008; Leconte et al. 2009).”
THE HEAVY-ELEMENT MASSES OF EXTRASOLAR GIANT PLANETS, REVEALED (2011, methodology): “A similar relationship has been found by using ad hoc enhanced atmospheric opacity to slow planetary contraction (Burrows et al. 2007).”
THE COMPOSITIONAL DIVERSITY OF EXTRASOLAR TERRESTRIAL PLANETS. I. IN SITU SIMULATIONS (2010, background): “Hints of such a correlation between transiting giant planets and stellar metallicity have been observed (Guillot et al. 2006; Burrows et al. 2007).”
Two Classes of Hot Jupiters (2007, methodology): “Using these models, we can repeat the exercises carried out by various other groups in the literature (e.g., Baraffe et al. 2005; Burrows et al. 2007), comparing our evolutionary models to the various planetary cases, using the proper stellar illumination to calculate the boundary conditions, in…”