Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanet

By J. Fraine, D. Deming, Björn Benneke, H. Knutson, A. Jord'an, Néstor Espinoza, N. Madhusudhan, A. Wilkins, K. Todorov. 2014

224 citations recorded by the source corpus.

Transmission spectroscopy has so far detected atomic and molecular absorption in Jupiter-sized exoplanets, but intense efforts to measure molecular absorption in the atmospheres of smaller (Neptune-sized) planets during transits have revealed only featureless spectra. From this it was concluded that the majority of small, warm planets evolve to sustain atmospheres with high mean molecular weights (little hydrogen), opaque clouds or scattering hazes, reducing our ability to observe the composition of these atmospheres. Here we report observations of the transmission spectrum of the exoplanet HAT-P-11b (which has a radius about four times that of Earth) from the optical wavelength range to the infrared. We detected water vapour absorption at a wavelength of 1.4 micrometres. The amplitude of the water absorption (approximately 250 parts per million) indicates that the planetary atmosphere is predominantly clear down to an altitude corresponding to about 1 millibar, and sufficiently rich in hydrogen to have a large scale height (over which the atmospheric pressure varies by a factor of e). The spectrum is indicative of a planetary atmosphere in which the abundance of heavy elements is no greater than about 700 times the solar value. This is in good agreement with the core-accretion theory of planet formation, in which a gas giant planet acquires its atmosphere by accreting hydrogen-rich gas directly from the protoplanetary nebula onto a large rocky or icy core.

Subfields: Astronomy and Astrophysics

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In Astronomy and Astrophysics

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

Citations in the corpus

• Water vapour in the atmosphere of the habitable-zone eight-Earth-mass planet K2-18 b (2019, methodology): “We identified three solutions: (1) a cloud-free atmosphere containing only H2O and H2–He, (2) a cloud-free atmosphere containing H2O, H2–He and N2 and (3) a cloudy atmosphere containing only H2O and H2–He.”
• The Complete Transmission Spectrum of WASP-39b with a Precise Water Constraint (2017, methodology): “…atmospheric water absorption features in exoplanet atmospheres have been used with retrieval modeling to constrain the overall atmospheric metallicity using oxygen as a proxy for the heavy element abundance (Kreidberg et al. 2014; Fraine et al. 2014; Kreidberg et al. 2015; Wakeford et al. 2017).”
• Pale Orange Dots: The Impact of Organic Haze on the Habitability and Detectability of Earthlike Exoplanets (2016, background): “In fact, the only sub-Neptunesized planet currently known to have an obviously clear atmosphere is HAT-P-11b (Fraine et al. 2014).”
• A NEW APPROACH TO ANALYZING HST SPATIAL SCANS: THE TRANSMISSION SPECTRUM OF HD 209458 b (2015, background): “…HST guiding system is stable, it fails to reset at exactly the same position as it was before a spatial scanning observation, causing horizontal position shifts of about one pixel over an entire visit (Deming et al. 2013; Kreidberg et al. 2014b; Knutson et al. 2014b; Fraine et al. 2014).”
• The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets (2017, background): “…in transit spectroscopy studies to constrain the contribution of unocculted photospheric heterogeneities to exoplanet transmission spectra (Pont et al. 2008; Sing et al. 2011; Huitson et al. 2013; Jordán et al. 2013; Pont et al. 2013; Fraine et al. 2014; Sing et al. 2016; Rackham et al. 2017).”
• NO THERMAL INVERSION AND A SOLAR WATER ABUNDANCE FOR THE HOT JUPITER HD 209458B FROM HST/WFC3 SPECTROSCOPY (2016, background): “…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).”
• BREEDING SUPER-EARTHS AND BIRTHING SUPER-PUFFS IN TRANSITIONAL DISKS (2015, background): “The atmosphere of HAT-P-11b may have patchy clouds (Line & Parmentier, in preparation) or be cloud-free; the latter interpretation still implicates a supersolar metallicity (Z & 0.6), as judged from the planet’s water absorption feature (Fraine et al. 2014, their Figures 2 and 3).”
• A Population Study of Gaseous Exoplanets (2017, background): “…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. 2014; Knutson et al. 2014a; Morello et al. 2015) and super-Earths (e.g. Bean et al. 2010; Berta et al. 2012; Knutson et al. 2014b;…”
• Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects (2019, unknown): “H2O HD 189733b (178), HD 209458b (63), WASP-12b (133), WASP-17b (171), WASP-19b (112), WASP-39b (276), WASP-43b (132), WASP-52b (266), WASP-63b (123), WASP-69b (266), WASP-76b (266), WASP-121b (77), HAT-P-1b (275), HAT-P-11b (84), HAT-P-18b (266), HAT-P-26b (277), HAT-P-32b (60), HAT-P-41b (266), XO”
• ExoMol molecular line lists XXX: a complete high-accuracy line list for water (2018, background): “At slightly lower temperatures, water was the first molecule to be observed in exoplanetary atmospheres (Tinetti et al. 2007) and it is now known to be a common constituent of hot Jupiters (Beaulieu et al. 2010; Iyer et al. 2016) and other exoplanets (Fraine et al. 2014).”
• Equilibrium chemistry down to 100 K (2017, background): “…wavelengths to analyse e.g. the chemical composition of brown dwarfs (see Allard et al. 1997; Helling & Casewell 2014 and references in these reviews) and exoplanets (e.g. Désert et al. 2008; Grillmair et al. 2008; de Kok et al. 2013; Kreidberg et al. 2014; Fraine et al. 2014; Birkby et al. 2017).”
• DETECTION OF AN ATMOSPHERE AROUND THE SUPER-EARTH 55 CANCRI E (2015, methodology): “…the saturation of the detector and has already been successfully used to provide an increasing number of exoplanetary spectra (e.g. Deming et al. 2013; Knutson et al. 2014a,b; Kreidberg et al. 2014a,b, 2015; McCullough et al. 2014; Crouzet et al. 2014; Fraine et al. 2014; Stevenson et al. 2014).”
• THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA (2015, methodology): “The degeneracy between uniform clouds and high mean molecular weight has already been investigated in a variety of planets (Benneke & Seager 2013; Knutson et al. 2014; Fraine et al. 2014).”
• CHARACTERIZING TRANSITING EXOPLANET ATMOSPHERES WITH JWST (2015, methodology): “Simultaneous photometric observations at relatively short wavelengths (e.g., see Fraine et al. 2014) could be used to correct this effect, and this may be possible with NIRCam λ ≤ 2.4 µm imaging during the NIRCam λ = 2.5− 5.0 µm grism spectral observations.”
• Limb darkening and exoplanets: testing stellar model atmospheres and identifying biases in transit parameters (2015, unknown): “We also remove Kepler-3b (HAT-P-11b) from our sample because its host star has been shown to have a significant amount of activity (Fraine et al. 2014) and thus the LDCs might be significantly biased (Csizmadia et al. 2013).”