The effect of condensates on the characterization of transiting planet atmospheres with transmission spectroscopy

By Jon Fortney. 2005

229 citations recorded by the source corpus.

Through a simple physical argument we show that the slant optical depth through the atmosphere of a ‘hot Jupiter’ planet is ∼35‐90 times greater than the normal optical depth. This not unexpected result has direct consequences for the method of transmission spectroscopy for characterizing the atmospheres of transiting giant planets. The atmospheres of these planets likely contain minor condensates and hazes, which at normal viewing geometry have negligible optical depth, but at slant viewing geometry have appreciable optical depth that can obscure absorption features of gaseous atmospheric species. We identify several possible condensates. We predict that this is a general masking mechanism for all planets, not just for HD 209458b, and will lead to weaker than expected or undetected absorption features. Constraints on an atmosphere from transmission spectroscopy are not the same as constraints on an atmosphere at normal viewing geometry. Ke yw ords: radiative transfer ‐ planetary systems.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/3243ec8f400db9b56e9fe4a57ed9543aedde947a

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In Astronomy and Astrophysics

1. N. Madhusudhan
2. Jon Fortney
3. A. Showman
4. M. Marley
5. D. Sing
6. D. Deming
7. H. Knutson
8. M. Line

Citations in the corpus

• An HST optical-to-near-IR transmission spectrum of the hot Jupiter WASP-19b: detection of atmospheric water and likely absence of TiO (2013, background): “…whether clouds or hazes should be dominant in the upper atmosphere of WASP-19b because, although photochemistry may have a role in producing high-altitude hazes, the temperature of the planet is too hot for many condensates to form, such as MgSiO3, Mg2SiO4 and iron-based condensates (Fortney 2005).”
• From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context (2018, unknown): “6 of Fortney 2005).”
• Dynamics and Disequilibrium Carbon Chemistry in Hot Jupiter Atmospheres, with Application to HD 209458b (2006, background): “As discussed by Fortney (2005), however, the slant geometry implies that even a layer of modest optical thickness could hide the signature of CO.”
• A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres (2007, background): “Although condensates are still an attractive option (Fortney et al. 2003; Fortney 2005), if TiO/VO are found on the day side of the planet’s limb, opacity due to these molecules from∼ 400 to 1000 nm could swamp the expected Na absorption feature at 589 nm.”
• THE IMPRINT OF EXOPLANET FORMATION HISTORY ON OBSERVABLE PRESENT-DAY SPECTRA OF HOT JUPITERS (2016, background): “The reason for this is the clouds’ higher optical depth when probed under transit geometry which obscure the molecular features (Fortney 2005).”
• DISEQUILIBRIUM CARBON, OXYGEN, AND NITROGEN CHEMISTRY IN THE ATMOSPHERES OF HD 189733b AND HD 209458b (2011, background): “…the inferred presence of hazes, clouds, and Rayleigh scatterers that can affect atmospheric spectral behavior (e.g., Charbonneau et al. 2002; Fortney et al. 2003; Fortney 2005; Iro et al. 2005; Pont et al. 2008; Lecavelier des Etangs et al. 2008a,b; Sing et al. 2008a,b, 2009; Shabram et al. 2011).”
• HST hot-Jupiter transmission spectral survey: evidence for aerosols and lack of TiO in the atmosphere of WASP-12b (2013, background): “Solar system observations and brown dwarf models indicate condensate scale heights which are ∼1/3 that of the local gas scale height (Carlson et al. 1994; Marley et al. 2002), a possibility for hot-Jupiter atmospheres as well (Fortney 2005).”
• HD 209458b in new light: evidence of nitrogen chemistry, patchy clouds and sub-solar water (2017, background): “The first term in Equation 6 accounts for scattering due to high-altitude hazes, whilst the second term models the sharp cut-off in transmission due to the high optical depths encountered inside clouds in the transit geometry (Fortney 2005).”
• HST PanCET Program: A Cloudy Atmosphere for the Promising JWST Target WASP-101b (2017, methodology): “We convert this to the slant optical depth (Fortney 2005) for each species and compare their cloud mass.”
• The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations (2012, background): “Fortney (2005) studied the effect of condensates on the transmission spectrum specifically.”
• ATMOSPHERIC CIRCULATION OF HOT JUPITERS: COUPLED RADIATIVE-DYNAMICAL GENERAL CIRCULATION MODEL SIMULATIONS OF HD 189733b and HD 209458b (2008, unknown): “In any event, because theslantoptical depth exceeds thenormaloptical depth by a factor of∼ 50 (Fortney 2005), the data are nevertheless consistent with normal cloud optical depths≪ 1.”
• WATER VAPOR IN THE SPECTRUM OF THE EXTRASOLAR PLANET HD 189733b. I. THE TRANSIT (2014, background): “Due to their geometry of light rays grazing the terminator region (Fortney 2005), transmission spectra are more sensitive to clouds/haze and/or small atmospheric scale heights than day-side emission spectra, which have their own limitations.”
• Rayleigh scattering in the transit spectrum of HD 189733b (2008, background): “For condensates, the scale height Hc is often found to be significantly smaller than the gaseous scale height (Hc ∼ H/3) (Ackerman & Marley 2001; Fortney 2005).”
• TRANSMISSION SPECTRA OF THREE-DIMENSIONAL HOT JUPITER MODEL ATMOSPHERES (2009, background): “Following Fortney (2005), we find that the slant optical depth at 1µbar of an absorbing layer that shares the gaseous scale height is60 times larger than the normal optical depth.”
• CHARACTERIZING TRANSITING EXOPLANET ATMOSPHERES WITH JWST (2015, background): “Although clouds can dominate transmission spectra, they may have a lessened impact on emission spectra due to their reduced effective optical depths (Fortney 2005).”
• Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life (2017, background): “Although transmission spectroscopy can enhance the signature of gases with low abundances through path length effects (e.g., Fortney, 2005), this advantage is relevant only for gases with a presence in the portions of the atmosphere probed by transmission spectroscopy.”
• TRANSITIONS IN THE CLOUD COMPOSITION OF HOT JUPITERS (2016, background): “Note that other minor species not considered here might become important at the limb because of the slant geometry and increase the cloud optical depth (Fortney 2005).”
• Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS (2009, background): “This is explained by the fact that the slant transit geometry probes atmospheres at high altitude and is more sensitive to low absorption cross-sections, while the normal viewing geometry of emission spectra probes deeper in the atmosphere (Fortney 2005).”