A DETECTION OF WATER IN THE TRANSMISSION SPECTRUM OF THE HOT JUPITER WASP-12b AND IMPLICATIONS FOR ITS ATMOSPHERIC COMPOSITION

By Laura Kreidberg, M. Line, J. Bean, Kevin B. Stevenson, J. D'esert, N. Madhusudhan, Jon Fortney, J. Barstow, G. Henry, M. Williamson and 1 more. 2015

200 citations recorded by the source corpus.

Detailed characterization of exoplanets has begun to yield measurements of their atmospheric properties that constrain the planets’ origins and evolution. For example, past observations of the dayside emission spectrum of the hot Jupiter WASP-12b indicated that its atmosphere has a high carbon-to-oxygen ratio (C/O > 1), suggesting it had a different formation pathway than is commonly assumed for giant planets. Here we report a precise near-infrared transmission spectrum for WASP-12b based on six transit observations with the Hubble Space Telescope/Wide Field Camera 3. We bin the data in 13 spectrophotometric light curves from 0.84 to 1.67 μm and measure the transit depths to a median precision of 51 ppm. We retrieve the atmospheric properties using the transmission spectrum and find strong evidence for water absorption (7σ confidence). This detection marks the first high-confidence, spectroscopic identification of a molecule in the atmosphere of WASP-12b. The retrieved 1 σ water volume mixing ratio is between 10−5 and 10−2, which is consistent with C/O > 1 to within 2σ. However, we also introduce a new retrieval parameterization that fits for C/O and metallicity under the assumption of chemical equilibrium. With this approach, we constrain C/O to 0.5 − 0.3 + 0.2 ?> at 1σ and rule out a carbon-rich atmosphere composition (C/O > 1) at >3σ confidence. Further observations and modeling of the planet’s global thermal structure and dynamics would aid in resolving the tension between our inferred C/O and previous constraints. Our findings highlight the importance of obtaining high-precision data with multiple observing techniques in order to obtain robust constraints on the chemistry and physics of exoplanet atmospheres.

Subfields: Astronomy and Astrophysics, Instrumentation

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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. V. Parmentier
6. D. Sing
7. J. D'esert
8. Laura Kreidberg

Citations in the corpus

• A CONSISTENT RETRIEVAL ANALYSIS OF 10 HOT JUPITERS OBSERVED IN TRANSMISSION (2016, methodology): “…these methods have been applied to observations of transiting extrasolar planets (e.g. Lee et al. 2012; Line et al. 2013b; Stevenson et al. 2014a; Kreidberg et al. 2014, 2015; Benneke 2015; Waldmann et al. 2015), although in many cases there has been considerable degeneracy that has prevented…”
• 2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules (2018, unknown): “…[1] Barman et al. (2011) [2] Barman et al. (2015) [3] Deming et al. (2013) [4] Haynes et al. (2015) [5] Kreidberg et al. (2014) [6] Kreidberg et al. (2015) [7] Lanotte et al. (2014) [8] Lockwood et al. (2014) [9] Madhusudhan et al. (2011) [10] Nugroho et al. (2017) [11] Sedaghati…”
• THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA (2015, methodology): “We use a transit transmission forward model (Line et al. 2013; Swain, Line, & Deroo 2014; Kreidberg et al. 2014b;15) to generate a variety of spectra over the HST WFC3 bandpass to illustrate the basic concept.”
• DETECTION OF H2O AND EVIDENCE FOR TiO/VO IN AN ULTRA-HOT EXOPLANET ATMOSPHERE (2016, background): “In the near-infrared, water absorption has now been robustly measured for a number of planets, both in transmission and emission (e.g. Deming et al. 2013; Wakeford et al. 2013; Stevenson et al. 2014; McCullough et al. 2014; Kreidberg et al. 2015).”
• From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context (2018, methodology): “More recently, retrieval models have begun incorporating more thorough forward models including chemical equilibrium calculations (e.g., Benneke 2015; Kreidberg et al. 2015) and H− opacities (Arcangeli et al. 2018).”
• H2O abundances and cloud properties in ten hot giant exoplanets (2018, methodology): “We show examples of simulated retrievals for data quality representative of WASP-12b, which has relatively moderate data quality compared to the planets in the ensemble.”
• NO THERMAL INVERSION AND A SOLAR WATER ABUNDANCE FOR THE HOT JUPITER HD 209458B FROM HST/WFC3 SPECTROSCOPY (2016, methodology): “…exoplanets are rapidly transforming our knowledge of planetary atmospheres (Berta et al. 2012; Swain et al. 2012; Deming et al. 2013; Huitson et al. 2013; Kreidberg et al. 2014ab,15; Stevenson et al. 2014c; McCullough et al. 2014; Knutson et al. 2014; Fraine et al. 2014; Evans et al. 2016).”
• HD 209458b in new light: evidence of nitrogen chemistry, patchy clouds and sub-solar water (2017, background): “However, in almost all cases the amplitudes of H2O absorption features are significantly lower than those expected of a cloud-free solar-composition atmosphere – typically ∼2 scale heights (Deming et al. 2013; Kreidberg et al. 2015; Sing et al. 2016) instead of ∼5-10 (Madhusudhan et al. 2014a).”
• A NEW APPROACH TO ANALYZING HST SPATIAL SCANS: THE TRANSMISSION SPECTRUM OF HD 209458 b (2015, background): “This behaviour supports the hypothesis that while the exponential “ramp” is a common-mode between the white and the spectral-light curve, the linear “ramp” is not, as seen in previous WFC3 observations (e.g. Deming et al. 2013; Fraine et al. 2014; Wilkins et al. 2014; Kreidberg et al. 2015).”
• Chemical enrichment of giant planets and discs due to pebble drift (2017, background): “Current observations of hot Jupiters are often consistent with either elevated C/O ratios or possibly C/O ratios close to that of their host star as the uncertainties remain significant (e.g. Line et al. 2014; Madhusudhan et al. 2014a; Kreidberg et al. 2015; Brewer et al. 2017).”
• Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects (2019, unknown): “Chemical Consequences of the C/O Ratio on Hot Jupiters: Examples from WASP-12b, CoRoT-2b, XO-1b, and HD 189733b. ApJ, 763:25, January 2013.”
• A Population Study of Gaseous Exoplanets (2017, methodology): “…et al. 2013; Todorov et al. 2013; McCullough 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.…”
• CHARACTERIZING TRANSITING EXOPLANET ATMOSPHERES WITH JWST (2015, methodology): “HST NICMOS and HST WFC3 G141 find strong water absorption in about a dozen hot Jupiters (e.g., Kreidberg et al. 2014b, 2015; Deming et al. 2013; Crouzet et al. 2012; Swain et al. 2009) and a warm Neptune-sized planet (Fraine et al. 2014).”
• batman: BAsic Transit Model cAlculatioN in Python (2015, methodology): “This package is based on code that was used to model high-precision light curves obtained for atmosphere characterization (Kreidberg et al. 2014a, 2014b, 2015; Stevenson et al. 2014a, 2014b, 2014c, 2014d).”