NO THERMAL INVERSION AND A SOLAR WATER ABUNDANCE FOR THE HOT JUPITER HD 209458B FROM HST/WFC3 SPECTROSCOPY

By M. Line, Kevin B. Stevenson, J. Bean, J. D'esert, Jon Fortney, Laura Kreidberg, N. Madhusudhan, A. Showman, H. Diamond-Lowe. 2016

161 citations recorded by the source corpus.

The nature of the thermal structure of hot Jupiter atmospheres is one of the key questions raised by the characterization of transiting exoplanets over the past decade. There have been claims that many hot Jupiters exhibit atmospheric thermal inversions. However, these claims have been based on broadband photometry rather than the unambiguous identification of emission features with spectroscopy, and the chemical species that could cause the thermal inversions by absorbing stellar irradiation at high altitudes have not been identified despite extensive theoretical and observational effort. Here we present high-precision Hubble Space Telescope WFC3 observations of the dayside thermal emission spectrum of the hot Jupiter HD 209458b, which was the first exoplanet suggested to have a thermal inversion. In contrast to previous results for this planet, our observations detect water in absorption at 6.2σ confidence. When combined with Spitzer photometry, the data are indicative of a monotonically decreasing temperature with pressure over the range of 1–0.001 bars at 7.7σ confidence. We test the robustness of our results by exploring a variety of model assumptions, including the temperature profile parameterization, presence of a cloud, and choice of Spitzer data reduction. We also introduce a new analysis method to determine the elemental abundances from the spectrally retrieved mixing ratios with thermochemical self-consistency and find plausible abundances consistent with solar metallicity (0.06–10 × solar) and carbon-to-oxygen ratios less than unity. This work suggests that high-precision spectrophotometric results are required to robustly infer thermal structures and compositions of extrasolar planet atmospheres and to perform comparative exoplanetology.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

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

In Instrumentation

1. N. Madhusudhan
2. Jon Fortney
3. A. Showman
4. M. Line
5. D. Sing
6. V. Parmentier
7. J. D'esert
8. Laura Kreidberg

In Statistical and Nonlinear Physics

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

Citations in the corpus

• A Population Study of Gaseous Exoplanets (2017, methodology): “…et al. 2014; Snellen et al. 2014; Stevenson et al. 2014b; Zellem et al. 2014; Macintosh et al. 2015; Kreidberg et al. 2015; Iyer et al. 2016; Line et al. 2016; Tsiaras et al. 2016a) down to Neptune/Uranus (e.g. Stevenson et al. 2010; Fukui et al. 2013; Ehrenreich et al. 2014; Fraine et al.…”
• HST PanCET Program: A Cloudy Atmosphere for the Promising JWST Target WASP-101b (2017, methodology): “To correct for visit-long trends we test linear, quadratic, and a rising exponential plus linear function (Stevenson et al. 2014; Line et al. 2016).”
• Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects (2019, background): “H2O WASP-43b (132), HD 209458b (151), HD 189733b (59), WASP-121b (76), Kepler-13Ab (20), WASP-33b (102)”
• SPITZER PHASE CURVE CONSTRAINTS FOR WASP-43b AT 3.6 AND 4.5 μm (2016, methodology): “Our cloud model is parameterized with a cloud base pressure, scale height, and gray opacity (Line & Parmentier 2016; Line et al. 2016).”
• HD 209458b in new light: evidence of nitrogen chemistry, patchy clouds and sub-solar water (2017, background): “…of exoplanetary atmospheres, including chemical signatures (Snellen et al. 2010; Deming et al. 2013), temperature profiles (Haynes et al. 2015; Line et al. 2016), circulation patterns (Stevenson et al. 2014), clouds/hazes (Sing et al. 2016), and escape processes (Ehrenreich et al. 2015); for…”
• A NEW APPROACH TO ANALYZING HST SPATIAL SCANS: THE TRANSMISSION SPECTRUM OF HD 209458 b (2015, background): “Carbon monoxide has also been detected (Snellen et al. 2010) while more carbon species, such as methane and carbon dioxide, have been suggested (Swain et al. 2009b; Madhusudhan & Seager 2009; Line et al. 2016).”
• From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context (2018, background): “…profile”) will exhibit a spectrum with absorption features, and a thermal structure with decreasing temperature with increasing pressure (”inverted temperature profile”) will exhibit a spectrum with emission features (e.g., Fortney et al. 2008; Madhusudhan & Seager 2010; Line et al. 2016).”
• The Cosmic Shoreline: The Evidence that Escape Determines which Planets Have Atmospheres, and what this May Mean for Proxima Centauri B (2017, background): “ever, early reports of thermal inversions on hot Jupiters (e.g., on HD 209458b; Burrows et al. 2007; ?) have since been cast into doubt by analyses of more precise data of higher spectral resolution (Line et al. 2016). The hot thermosphere (and possibly warm stratosphere) suggests that escape from t”
• Equilibrium chemistry down to 100 K (2017, methodology): “Benneke (2015), Line et al. (2016) and Oreshenko Article number, page 2 of 34 et al. (2017) have shown that it is feasible to include equilibrium chemistry in exoplanet retrieval methods.”
• The Complete Transmission Spectrum of WASP-39b with a Precise Water Constraint (2017, background): “This becomes important when considering the impact differences in the limbs will have on the transmission spectrum which measures the average absorption profile of the limb annulus around the planet (e.g. Line et al. 2016).”
• H− Opacity and Water Dissociation in the Dayside Atmosphere of the Very Hot Gas Giant WASP-18b (2018, background): “This is surprising for such massive gas giants, as their expected formation channels imply that their metallicities should be close to their host stars’, as observed in their cooler counterparts (e.g., Kreidberg et al. 2014b; Benneke 2015; Line et al. 2016).”
• Global Climate and Atmospheric Composition of the Ultra-hot Jupiter WASP-103b from HST and Spitzer Phase Curve Observations (2018, background): “In cooler atmospheres, water is the dominant absorber over this bandpass (e.g. Kreidberg et al. 2014a; Line et al. 2016), but in WASP-103b, H2O is partially dissociated in the photosphere, leading to a drop in abundance by a factor of ∼ 10 (see Figure 12).”
• Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST (2017, methodology): “…of the detectors of course remains to be seen, but we are heartened by recent analyses of HST/WFC3 and Spitzer/IRAC data that consistently produce photon-noiselimited results down to a precision of 15 parts per million (e.g., Kreidberg et al. 2014; Ingalls et al. 2016; Line et al. 2016).”