MASSES, RADII, AND CLOUD PROPERTIES OF THE HR 8799 PLANETS

By M. Marley, D. Saumon, M. Cushing, A. Ackerman, Jon Fortney, R. Freedman. 2012

181 citations recorded by the source corpus.

The near-infrared colors of the planets directly imaged around the A star HR 8799 are much redder than most field brown dwarfs of the same effective temperature. Previous theoretical studies of these objects have concluded that the atmospheres of planets b, c, and d are unusually cloudy or have unusual cloud properties. Some studies have also found that the inferred radii of some or all of the planets disagree with expectations of standard giant planet evolution models. Here, we compare the available data to the predictions of our own set of atmospheric and evolution models that have been extensively tested against observations of field L and T dwarfs, including the reddest L dwarfs. Unlike some previous studies, we require mutually consistent choices for effective temperature, gravity, cloud properties, and planetary radius. This procedure thus yields plausible values for the masses, effective temperatures, and cloud properties of all three planets. We find that the cloud properties of the HR 8799 planets are not unusual but rather follow previously recognized trends, including a gravity dependence on the temperature of the L to T spectral transition—some reasons for which we discuss. We find that the inferred mass of planet b is highly sensitive to whether or not we include the H- and the K-band spectrum in our analysis. Solutions for planets c and d are consistent with the generally accepted constraints on the age of the primary star and orbital dynamics. We also confirm that, like in L and T dwarfs and solar system giant planets, non-equilibrium chemistry driven by atmospheric mixing is also important for these objects. Given the preponderance of data suggesting that the L to T spectral type transition is gravity dependent, we present an exploratory evolution calculation that accounts for this effect. Finally we recompute the bolometric luminosity of all three planets.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f962d0f52ae952ac2c994e67e12282b9cce1d906

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In Astronomy and Astrophysics

1. Michael C. Liu
2. Jon Fortney
3. M. Marley
4. B. Bowler
5. T. Dupuy
6. A. Burgasser
7. N. Madhusudhan
8. Adam Burrows

Citations in the corpus

• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e (2020, methodology): “7 in Morley et al. 2012, and Marley et al. 2012; Charnay et al. 2018).”
• NEGLECTED CLOUDS IN T AND Y DWARF ATMOSPHERES (2012, background): “Several studies of the HR 8799 planets have shown that the iron and silicate clouds play a significant role in their atmospheres (Marois et al. 2008; Barman et al. 2011; Galicher et al. 2011; Bowler et al. 2010; Currie et al. 2011; Madhusudhan et al. 2011; Marley et al. 2012).”
• The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations (2012, background): “The dashed line shows the gravity dependence of the disappearance of clouds below the photosphere according to Marley et al. (2012).”
• THE EXTREMELY RED, YOUNG L DWARF PSO J318.5338−22.8603: A FREE-FLOATING PLANETARY-MASS ANALOG TO DIRECTLY IMAGED YOUNG GAS-GIANT PLANETS (2013, background): “These properties are thought to arise from extreme atmospheric conditions tied to their young (≈10–30 Myr) ages and low gravities, e.g., enhanced vertical mixing, non-equilibrium chemistry, and unusual clouds (e.g. Barman et al. 2011b; Madhusudhan et al. 2011; Marley et al. 2012).”
• DIRECT IMAGING OF A COLD JOVIAN EXOPLANET IN ORBIT AROUND THE SUN-LIKE STAR GJ 504 (2013, background): “It has been proposed that planetary candidates with hot atmospheres (Teff ∼ 1000 K) around HR 8799 or 2M 1207 may have thick clouds (Barman et al. 2011a; Madhusudhan et al. 2011; Skemer et al. 2011; Marley et al. 2012) although their cloud properties are under discussion (Barman et al. 2011a,b).”
• On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, methodology): “…and thermal profile between strict two-stream solutions and general multi-stream solutions, and is the approach currently used in the Marley/Saumon brown dwarf and giant planet models (e.g., Marley et al. 2002; Fortney et al. 2005; Saumon & Marley 2008; Morley et al. 2012; Marley et al. 2012).”
• HST SPECTRAL MAPPING OF L/T TRANSITION BROWN DWARFS REVEALS CLOUD THICKNESS VARIATIONS (2013, methodology): “4, see also Skemer et al. 2012; Barman et al. 2011a,b; Currie et al. 2011; Madhusudhan et al. 2011; Marley et al. 2012).”
• A STUDY OF THE DIVERSE T DWARF POPULATION REVEALED BY WISE (2013, background): “37+113343.7 (Faherty et al. 2013), 2MASS 1207b (Patience et al. 2010; Barman et al. 2011a) and the HR 8799 planets (Bowler et al. 2010; Barman et al. 2011b; Marley et al. 2012) have low surface gravity, appear to be dusty, resemble the L dwarf standards, and lack the methane features of T dwarfs.”
• Wide-Field InfrarRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 Report (2015, background): “…consistent with a clearing of clouds as effective temperatures decrease to ~900 K (the L-T spectral type transition), but cool giant exoplanets, like those around HR 8799, seem to keep their clouds at these low temperatures, perhaps due to their lower surface gravities (e.g., Marley et al. 2012).”
• SIMULTANEOUS DETECTION OF WATER, METHANE, AND CARBON MONOXIDE IN THE ATMOSPHERE OF EXOPLANET HR 8799 b (2015, background): “Evidence for quenching of CO and CH4 in the atmospheres of the HR8799 planets has been established elsewhere (Hinz et al. 2010; Barman et al. 2011a; Skemer et al. 2012; Marley et al. 2012).”
• Imaging Extrasolar Giant Planets (2016, background): “…as a result of vigorous vertical mixing (e.g., Barman et al. 2011a; Zahnle & Marley 2014; Ingraham et al. 2014; Skemer et al. 2014a), while the preservation of photospheric condensates can be explained by a dependency of cloud base pressure and particle size on surface gravity (Marley et al. 2012).”
• THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS (2016, background): “Theoretical work (e.g., Barman et al. 2011b; Madhusudhan et al. 2011; Marley et al. 2012; Lee et al. 2013; Zahnle & Marley 2014) has helped provide physical context for direct imaging observations.”