Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity

By Jon Fortney, M. Marley, D. Saumon, K. Lodders. 2008

250 citations recorded by the source corpus.

We examine the spectra and infrared colors of the cool, methane-dominated atmospheres at Teff ⩽ 1400 K expected for young gas giant planets. We couple these spectral calculations to an updated version of the Marley et al. giant planet thermal evolution models that include formation by core accretion-gas capture. These relatively cool “young Jupiters” can be 1-6 mag fainter than predicted by standard cooling tracks that include a traditional initial condition, which may provide a diagnostic of formation. If correct, this would make true Jupiter-like planets much more difficult to detect at young ages than previously thought. Since Jupiter and Saturn are of distinctly supersolar composition, we examine emitted spectra for model planets at both solar metallicity and a metallicity of 5 times solar. These metal-enhanced young Jupiters have lower pressure photospheres than field brown dwarfs of the same effective temperatures arising from both lower surface gravities and enhanced atmospheric opacity. We highlight several diagnostics for enhanced metallicity. A stronger CO absorption band at 4.5 μm for the warmest objects is predicted. At all temperatures, enhanced flux in K band is expected due to reduced collisional induced absorption by H2. This leads to correspondingly redder near-infrared colors, which are redder than solar metallicity models with the same surface gravity by up to 0.7 in J − K and 1.5 in H − K. Molecular absorption band depths increase as well, most significantly for the coolest objects. We also qualitatively assess the changes to emitted spectra due to nonequilibrium chemistry.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/34de171738165024f62159eb12be80dce4030972

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In Astronomy and Astrophysics

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

In Instrumentation

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

Citations in the corpus

• MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS–AURIGA (2011, background): “However, more detailed models of planet formation by Marley et al. (2007) and Fortney et al. (2008) suggest that accretion shocks can dispel much of the initial energy, leading to lower internal entropy and initial temperatures.”
• A chemical model for the atmosphere of hot Jupiters (2012, background): “The first models of hot Jupiter atmospheres assumed chemical equilibrium (e.g. Burrows & Sharp 1999; Seager & Sasselov 2000; Sharp & Burrows 2007; Barman 2007; Burrows et al. 2007, 2008; Fortney et al. 2008a).”
• EXOPLANET ALBEDO SPECTRA AND COLORS AS A FUNCTION OF PLANET PHASE, SEPARATION, AND METALLICITY (2010, methodology): “…and §4, coarse spectra can be used in combination with atmospheric models to constrain the temperature, composition, the presence or absence of clouds in an exoplanet’s atmosphere, and the exoplanet’s radius (Marley et al. 1999a; Marley & McKay 1999b; Marley et al. 2007; Fortney et al. 2008a,b).”
• DIRECT IMAGING OF A COLD JOVIAN EXOPLANET IN ORBIT AROUND THE SUN-LIKE STAR GJ 504 (2013, background): “Adopting the Ks-band luminosity may result in a bias in the mass estimation, since this wavelength range is particularly sensitive to atmospheric parameters such as surface gravity and metallicity (Fortney et al. 2008; Spiegel & Burrows 2012; Janson et al. 2011).”
• A COMBINED SUBARU/VLT/MMT 1–5 μm STUDY OF PLANETS ORBITING HR 8799: IMPLICATIONS FOR ATMOSPHERIC PROPERTIES, MASSES, AND FORMATION (2011, background): “…will be developed and applied to HR 8799bcde and other planetary-mass objects in upcoming papers (Madhusudhan et al. 2011, in prep.) and may provide a useful comparison to planet parameters derived from cooling models (e.g. Burrows et al. 1997; Baraffe et al. 2003; Fortney et al. 2007, 2008).”
• PLANETS AROUND LOW-MASS STARS (PALMS). IV. THE OUTER ARCHITECTURE OF M DWARF PLANETARY SYSTEMS (2014, methodology): “For the cold start models we adopt the grid from Fortney et al. (2008), which assumes slight metal enrichment (5 times solar abundances), includes masses below 13 MJup, and focuses on relatively young ages (.1 Gyr).”
• LkCa 15: A YOUNG EXOPLANET CAUGHT AT FORMATION? (2011, background): “Also, evolutionary models make extremely discrepant predictions regarding the luminosity of planets as a function of age (Chabrier et al. 2000; Fortney et al. 2008), though this discussion is complicated by possible flux contributions from circumplanetary material and accretion luminosity.”
• NEGLECTED CLOUDS IN T AND Y DWARF ATMOSPHERES (2012, background): “While brown dwarfs are more massive than planets, the atmospheres of T dwarfs have similar effective temperatures to those of young giant planets (Burrows et al. 1997; Fortney et al. 2008).”
• SPECTRAL AND PHOTOMETRIC DIAGNOSTICS OF GIANT PLANET FORMATION SCENARIOS (2011, methodology): “If the dichotomy between initial conditions is as dramatic as in the fiducial models, then at early times there should be prominent observational differences (cf. M07; Fortney et al. 2008).”
• QUANTITATIVELY ASSESSING THE ROLE OF CLOUDS IN THE TRANSMISSION SPECTRUM OF GJ 1214b (2013, background): “…planets and moons, brown dwarfs, and exoplanets, with both cloudy and clear atmospheres; the models are described in McKay et al. (1989); Marley et al. (1996); Burrows et al. (1997); Marley & McKay (1999); Marley et al. (2002); Fortney et al. (2005); Saumon & Marley (2008); Fortney et al. (2008).”
• Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST (2017, methodology): “The TRAPPIST-1 spectrum is calculated for this paper using the radiative-convective atmosphere models described in McKay et al. (1989), Marley et al. (1996), Saumon & Marley (2008), Fortney et al. (2008), and Morley et al. (2015), assuming a dust-free model atmosphere.”
• NEAR-INFRARED SPECTROSCOPY OF THE EXTRASOLAR PLANET HR 8799 b (2010, background): “…et al. 1996; Alibert et al. 2005a) are generally predicted to have metal-rich atmospheres as a result of planetesimal accretion, the accretion of metal-rich gas, and/or core erosion (Alibert et al. 2005b; Guillot & Hueso 2006; Mousis et al. 2009; see Fortney et al. 2008 for a thorough summary).”
• AN ALL-SKY CATALOG OF BRIGHT M DWARFS (2011, background): “It is also possible that young giant planets may be less luminous and more difficult to detect than previously predicted (Fortney et al. 2008).”
• Imaging Extrasolar Giant Planets (2016, background): “Cold-start models were made prominent by Marley et al. (2007b) and Fortney et al. (2008) in the context of direct imaging as an attempt to emulate a more realistic formation scenario for giant planets through core accretion.”
• DISEQUILIBRIUM CARBON, OXYGEN, AND NITROGEN CHEMISTRY IN THE ATMOSPHERES OF HD 189733b AND HD 209458b (2011, background): “On HD 189733b, CO2 quenches eventually (see where dotted curve diverges from dashed curve), but only at very high altitudes, and its abundance follows equilibrium at the pressure levels at which the observations are the most sensitive (∼1–10−4 bar, see Fortney et al. 2008a).”
• WATER, METHANE, AND CARBON DIOXIDE PRESENT IN THE DAYSIDE SPECTRUM OF THE EXOPLANET HD 209458b (2009, methodology): “Mid-infrared dayside photometry (Knutson et al. 2008) provides evidence for an atmospheric temperature inversion (Burrows, et al. 2007) and has been used to support a classification scheme for the hot-Jupiter type exoplanets (Fortney et al. 2008).”