On the Radii of Extrasolar Giant Planets

By P. Bodenheimer, Gregory Laughlin, D. Lin. 2003

237 citations recorded by the source corpus.

We have computed evolutionary models for extrasolar planets that range in mass from 0.1MJ to 3.0MJ and that range in equilibrium temperature from 113 to 2000 K. We present four sequences of models, designed to show the structural effects of a solid (20 M⊕) core and of internal heating due to the conversion of kinetic to thermal energy at pressures of tens of bars. The model radii at ages of 4-5 Gyr are intended for future comparisons with radii derived from observations of transiting extrasolar planets. To provide such comparisons, we expect that of order 10 transiting planets with orbital periods less than 200 days can be detected around bright (V < 10-11) main-sequence stars, for which accurate well-sampled radial velocity (RV) measurements can also be readily accumulated. Through these observations, structural properties of the planets will be derivable, particularly for low-mass, high-temperature planets. Implications regarding the transiting companion to OGLE-TR-56 recently announced by Konacki et al. are discussed. With regard to the transiting planet HD 209458b, we find, in accordance with other recent calculations, that models without internal heating predict a radius that is ~0.3RJ smaller than the observed radius. Two resolutions have been proposed for this discrepancy. Guillot & Showman hypothesize that deposition of kinetic wind energy at pressures of tens of bars is responsible for heating the planet and maintaining its large size. Our models confirm that dissipation of the type proposed by Guillot & Showman can indeed produce a large radius for HD 209458b. Bodenheimer, Lin, & Mardling suggest that HD 209458b owes its large size to dissipation of energy arising from ongoing tidal circularization of the planetary orbit. This mechanism requires the presence of an additional planetary companion to continuously force the eccentricity. We show that residual scatter in the current RV data set for HD 209458b is consistent with the presence of an as-of-yet undetected second companion and that further RV monitoring of HD 209458 is indicated. Tidal circularization theory also can provide constraints on planetary radii. Extrasolar giant planets with periods of order 7 days should be actively circularizing. We find that the observed eccentricities of e ~ 0.14 for both HD 217107b (P = 6.276 days; M sin i = 1.80MJ) and HD 68988b (P = 7.125 days, M sin i = 1.29MJ) likely indicate either relatively small planetary radii for these objects (R ~ 1.1RJ) or tidal quality factors in the neighborhood of QP ~ 107. For these two planets, it will be difficult to differentiate the contribution from tidal and kinetic heating. But the radius of HD 168746b (P = 6.403 days, M sin i = 0.23MJ) is sensitive to whether the planet's interior is heated by tidal dissipation or kinetic heating. The tidal circularization timescale of this planet is shorter than the age of its host star, but we show that within the observational uncertainties, the published RV data can also be fitted with a circular orbit for this planet. As more RV planets with periods of order 1 week are discovered, QP(Teq,MP) and RP(Teq,MP) will become better determined.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/fa8e51bb17064b016ed9cd1709d8a80261b30e2e

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In Astronomy and Astrophysics

1. Jon Fortney
2. D. Charbonneau
3. Sara Seager
4. N. Madhusudhan
5. J. Southworth
6. J. Winn
7. M. Marley
8. A. Showman

Citations in the corpus

• Using Stellar Limb-Darkening to Refine the Properties of HD 209458b (2006, background): “Because the timescale for orbital circularization is shorter than the age of the system by a factor of 100 (Cody & Sasselov 2002; Bodenheimer et al. 2003), one way to produce a nonzero eccentricity for HD 209458b would be to have a second planet pumping up its eccentricity (Bodenheimer et al. 2001,…”
• A Transiting Planet of a Sun-like Star (2006, background): “The radius of each of these two large planets, ∼1.3 times the radius of Jupiter, is ∼20% larger than theoretical models predict (Table 1 of Bodenheimer et al. 2003).”
• ON THE ANOMALOUS RADII OF THE TRANSITING EXTRASOLAR PLANETS (2011, methodology): “Our baseline models were published by Bodenheimer et al. (2003); hereafter BLL.”
• IN SITU FORMATION AND DYNAMICAL EVOLUTION OF HOT JUPITER SYSTEMS (2015, methodology): “…discussed in the literature, and has been used to calculate the formation phases of both, solar system planets (e.g. Pollack et al. 1996; Hubickyj et al. 2005; Helled et al. 2014), as well as extrasolar planets 3 (Bodenheimer et al. 2003; Dodson-Robinson and Bodenheimer 2009; Rogers et al. 2011).”
• Improving Stellar and Planetary Parameters of Transiting Planet Systems: The Case of TrES-2 (2007, background): “In the past, this anomaly was explained invoking a source of internal heat (e.g., Bodenheimer et al. 2001, 2003; Guillot & Showman, 2002; Winn & Holman 2005), either through eccentricity pumping bymore distant companions or through persisting obliquity tides.”
• Predicting low-frequency radio fluxes of known extrasolar planets (2007, methodology): “Using the data of Bodenheimer et al. (2003), we use the following fit for the radius increase r: r = 1 + 0.05 ( Teq T0 )γ .”
• Five New Multicomponent Planetary Systems (2005, methodology): “The transit durations are calculated from the orbital elements, while the transit depths are derived from the estimated stellar radii and the planetary radii from the models of Bodenheimer et al. (2003).”
• Tidal Heating of Extrasolar Planets (2008, background): “Heat sources that have been considered in these models include the energy of planetary accretion and radiation from the star, as well as tidal heating (Bodenheimer et al. 2003;Winn&Holman2005;Mardling 2007).”
• Possible Solutions to the Radius Anomalies of Transiting Giant Planets (2006, background): “Many workers have sought to explain the large radii of transiting planets such as HAT-P1b,WASP-1b, and HD 209458b by invoking an extra power source in the planet’s interior (Bodenheimer et al. 2003; Guillot & Showman 2002; Winn & Holman 2005; Chabrier et al. 2004; Charbonneau et al. 2007b).”
• LACK OF INFLATED RADII FOR KEPLER GIANT PLANET CANDIDATES RECEIVING MODEST STELLAR IRRADIATION (2011, background): “Bodenheimer et al. (2003) proposed that an additional companion in the system could pump the planet eccentricity that would be dissipated through tides.”
• Improving the Efficiency of Markov Chain Monte Carlo for Analyzing the Orbits of Extrasolar Planets (2005, background): “Bodenheimer et al. (2003) offered a potential explanation, namely, that the radius could be inflated due to tidal heating if the planet still had an eccentricity of ’0.03.”
• Tidal Evolution of Close-in Extrasolar Planets (2007, background): “The implications of this hypothesis for planetary masses Mp , radii Rp , and heating rates has been considered in previous studies (Rasio et al. 1996; Trilling 2000; Bodenheimer et al. 2003).”