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

Fraine, Jonathan and Deming, Drake and Benneke, Björn and Knutson, Heather and Jordán, Andrés and Espinoza, Néstor and Madhusudhan, Nikku and Wilkins, Ashlee and Todorov, Kamen (2014) Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanet. Nature, 513 (7519). pp. 526-529. ISSN 0028-0836.

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[img] Image (JPEG) (Extended Data Figure 1: HST white-light curve with exponential ramp effects.) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 2: An example of WFC3 scanning-mode observation spectral images.) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 3: Correlations between all fitted parameters for our HST WFC3 white-light curve.) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 4: Wavelength-dependent transit light curves.) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 5: The distribution of Kepler starspot crossing anomalies.) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 6: HAT-P-11 Kepler light curve for ~4 yr of short cadence.) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 1: Transit depths as a function of wavelength for Kepler, HST WFC3, Spitzer IRAC1 and Spitzer IRAC2) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 2: The system and planetary parameters of HAT-P-11b) - Supplemental Material
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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.

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URLURL TypeDescription DOIArticle ReadCube access Paper
Fraine, Jonathan0000-0003-0910-5805
Deming, Drake0000-0001-5727-4094
Benneke, Björn0000-0001-5578-1498
Knutson, Heather0000-0002-0822-3095
Espinoza, Néstor0000-0001-9513-1449
Madhusudhan, Nikku0000-0002-4869-000X
Todorov, Kamen0000-0002-9276-8118
Alternate Title:Water Vapor Absorption in the Clear Atmosphere of an exo-Neptune
Additional Information:© 2014 Macmillan Publishers Limited. Received 04 April 2014; Accepted 07 August 2014; Published online 24 September 2014. J.F., A.J. and N.E. acknowledge support from project IC120009 ‘Millennium Institute of Astrophysics (MAS)’ of the Millennium Science Initiative, Chilean Ministry of Economy; FONDECYT project 1130857; and BASAL CATA PFB-06. N.E. is supported by CONICYT-PCHA/Doctorado Nacional. We thank P. McCullough for his assistance in the planning and execution of our observations. We are grateful to I. Crossfield, L. Kreidberg and E. Agol for providing their open-source, Python code banks on their individual websites. We are also grateful for discussions with M. Line, J. Fortney and J. Moses about the nature of photochemistry and interior structures. We thank the ATLAS and PHOENIX teams for providing stellar models. We also thank the SciPy and NumPy associations for providing extensive and rigorous numerical routines for an assortment of mathematical and computational techniques. Author Contributions: J.F. led the data analysis for this project with contributions from D.D., H.K., N.E., A.J. and A.W. A.W. supplied Hubble spectral fitting routines and interpretations. N.E. and A.J. supplied Python routines for MCMC, wavelet and transit curve analyses specific to transiting exoplanets. D.D., H.K., N.E. and A.J. provided computational equipment and administration. D.D., N.M., H.K. and K.T. successfully applied for and provided data from Hubble. B.B. and N.M. provided atmospheric models and accompanying fits. B.B. performed atmospheric retrieval analysis and provided figures and interpretations. N.E. supplied stellar limb-darkening coefficients calculated from both ATLAS and PHOENIX models.
Funding AgencyGrant Number
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y TurismoIC120009
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1130857
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)UNSPECIFIED
Subject Keywords:Atmospheric chemistry; Exoplanets
Issue or Number:7519
Record Number:CaltechAUTHORS:20141017-095611623
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50485
Deposited By: Tony Diaz
Deposited On:17 Oct 2014 17:54
Last Modified:14 Oct 2019 23:04

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