A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion

Abstract

Thousands of transiting exoplanets have been discovered, but spectral analysis of their atmospheres has so far been dominated by a small number of exoplanets and data spanning relatively narrow wavelength ranges (such as 1.1–1.7 micrometres). Recent studies show that some hot-Jupiter exoplanets have much weaker water absorption features in their near-infrared spectra than predicted1,2,3,4,5. The low amplitude of water signatures could be explained by very low water abundances6,7,8, which may be a sign that water was depleted in the protoplanetary disk at the planet’s formation location9, but it is unclear whether this level of depletion can actually occur. Alternatively, these weak signals could be the result of obscuration by clouds or hazes1,2,3,4, as found in some optical spectra3,4,10,11. Here we report results from a comparative study of ten hot Jupiters covering the wavelength range 0.3–5 micrometres, which allows us to resolve both the optical scattering and infrared molecular absorption spectroscopically. Our results reveal a diverse group of hot Jupiters that exhibit a continuum from clear to cloudy atmospheres. We find that the difference between the planetary radius measured at optical and infrared wavelengths is an effective metric for distinguishing different atmosphere types. The difference correlates with the spectral strength of water, so that strong water absorption lines are seen in clear-atmosphere planets and the weakest features are associated with clouds and hazes. This result strongly suggests that primordial water depletion during formation is unlikely and that clouds and hazes are the cause of weaker spectral signatures.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: HST/Spitzer transmission spectral sequence of hot-Jupiter survey targets.
Figure 2: Pressure–temperature profiles and condensation curves.
Figure 3: Transmission spectral index diagram of ΔZJ − LM versus H2O amplitude.

References

  1. 1

    Deming, D. et al. Infrared transmission spectroscopy of the exoplanets HD 209458b and XO-1b using the Wide Field Camera-3 on the Hubble Space Telescope . Astrophys. J. 774, 95 (2013)

    ADS  Google Scholar 

  2. 2

    Line, M. R. et al. A near-infrared transmission spectrum for the warm Saturn Hat-P-12b. Astrophys. J. 778, 183 (2013)

    ADS  Google Scholar 

  3. 3

    Sing, D. K. et al. HST hot-Jupiter transmission spectral survey: evidence for aerosols and lack of TiO in the atmosphere of WASP-12b. Mon. Not. R. Astron. Soc. 436, 2956–2973 (2013)

    ADS  CAS  Google Scholar 

  4. 4

    Sing, D. K. et al. HST hot-Jupiter transmission spectral survey: detection of potassium in WASP-31b along with a cloud deck and Rayleigh scattering. Mon. Not. R. Astron. Soc. 446, 2428–2443 (2015)

    ADS  CAS  Google Scholar 

  5. 5

    McCullough, P. R. et al. Water vapor in the spectrum of the extrasolar planet HD 189733b. I. The transit. Astrophys. J. 791, A55 (2014)

    ADS  Google Scholar 

  6. 6

    Madhusudhan, N. et al. H2O abundances in the atmospheres of three hot Jupiters. Astrophys. J. 791, L9 (2014)

    ADS  Google Scholar 

  7. 7

    Madhusudhan, N. et al. Toward chemical constraints on hot Jupiter migration. Astrophys. J. 794, L12 (2014)

    ADS  Google Scholar 

  8. 8

    Seager, S. et al. On the dayside thermal emission of hot Jupiters. Astrophys. J. 632, 1122–1131 (2005)

    ADS  CAS  Google Scholar 

  9. 9

    Öberg, K. I., Murray-Clay, R. & Bergin, E. A. The effects of snowlines on C/O in planetary atmospheres. Astrophys. J. 743, L16 (2011)

    ADS  Google Scholar 

  10. 10

    Pont, F. et al. The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations. Mon. Not. R. Astron. Soc . 432, 2917–2944 (2013)

    ADS  Google Scholar 

  11. 11

    Nikolov, N. et al. HST hot-Jupiter transmission spectral survey: haze in the atmosphere of WASP-6b. Mon. Not. R. Astron. Soc. 447, 463–478 (2015)

    ADS  CAS  Google Scholar 

  12. 12

    Nikolov, N. et al. Hubble Space Telescope hot Jupiter transmission spectral survey: a detection of Na and strong optical absorption in HAT-P-1b. Mon. Not. R. Astron. Soc. 437, 46–66 (2014)

    ADS  CAS  Google Scholar 

  13. 13

    Wakeford, H. R. et al. HST hot Jupiter transmission spectral survey: detection of water in HAT-P-1b from WFC3 near-IR spatial scan observations. Mon. Not. R. Astron. Soc. 435, 3481–3493 (2013)

    ADS  Google Scholar 

  14. 14

    Huitson, C. M. et al. An HST optical to near-IR transmission spectrum of the hot Jupiter Wasp-19b: detection of atmospheric water and likely absence of TiO. Mon. Not. R. Astron. Soc. 434, 3252–3274 (2013)

    ADS  CAS  Google Scholar 

  15. 15

    Mandel, K. & Agol, E. Analytic light curves for planetary transit searches. Astrophys. J. 580, L171–L175 (2002)

    ADS  Google Scholar 

  16. 16

    Pont, F., Zucker, S. & Queloz, D. The effect of red noise on planetary transit detection. Mon. Not. R. Astron. Soc. 373, 231–242 (2006)

    ADS  Google Scholar 

  17. 17

    Fortney, J. J. et al. A unified theory for the atmospheres of the hot and very hot Jupiters: two classes of irradiated atmospheres. Astrophys. J. 678, 1419–1435 (2008)

    ADS  CAS  Google Scholar 

  18. 18

    Burrows, A. et al. Photometric and spectral signatures of three-dimensional models of transiting giant exoplanets. Astrophys. J. 719, 341–350 (2010)

    ADS  CAS  Google Scholar 

  19. 19

    Seager, S. & Sasselov, D. D. Theoretical transmission spectra during extrasolar giant planet transits. Astrophys. J. 537, 916–921 (2000)

    ADS  CAS  Google Scholar 

  20. 20

    Lodders, K. Jupiter formed with more tar than ice. Astrophys. J. 611, 587–597 (2004)

    ADS  CAS  Google Scholar 

  21. 21

    Mousis, O., Lunine, J. I., Madhusudhan, N. & Johnson, T. V. Nebular water depletion as the cause of Jupiter’s low oxygen abundance. Astrophys. J. 751, L7 (2012)

    ADS  Google Scholar 

  22. 22

    Wong, M. H. et al. Updated Galileo probe mass spectrometer measurements of carbon, oxygen, nitrogen, and sulfur on Jupiter. Icarus 171, 153–170 (2004)

    ADS  CAS  Google Scholar 

  23. 23

    Kreidberg, L. et al. Clouds in the atmosphere of the super-Earth GJ 1214b. Nature 505, 69–72 (2014)

    ADS  PubMed  Google Scholar 

  24. 24

    Knutson, H. et al. Hubble Space Telescope near-IR transmission spectroscopy of the super-Earth HD 97658b. Astrophys. J. 794, A155 (2014)

    ADS  Google Scholar 

  25. 25

    Morley, C. V. et al. Neglected clouds in T and Y dwarf atmospheres. Astrophys. J. 756, 172 (2012)

    ADS  Google Scholar 

  26. 26

    Wakeford, H. R. & Sing, D. K. Transmission spectral properties of clouds for hot Jupiter exoplanets. Astron. Astrophys. 573, A122 (2015)

    ADS  Google Scholar 

  27. 27

    Showman, A. P. & Polvani, L. M. Equatorial superrotation on tidally locked exoplanets. Astrophys. J. 738, 71 (2011)

    ADS  Google Scholar 

  28. 28

    Oshagh, M. et al. Impact of occultations of stellar active regions on transmission spectra. Astron. Astrophys. 568, A99 (2014)

    Google Scholar 

  29. 29

    Burgasser, A. J. et al. Evidence of cloud disruption in the L/T dwarf transition. Astrophys. J. 571, L151–L154 (2002)

    ADS  Google Scholar 

  30. 30

    Cushing, M. C., Rayner, J. T. & Vacca, W. D. An infrared spectroscopic sequence of M, L, and T dwarfs. Astrophys. J. 623, 1115–1140 (2005)

    ADS  CAS  Google Scholar 

  31. 31

    Mandell, A. M. et al. Exoplanet transit spectroscopy using WFC3: WASP-12 b, WASP-17 b, and WASP-19 b. Astrophys. J. 779, 128 (2013)

    ADS  Google Scholar 

  32. 32

    Sing, D. K. et al. Stellar limb-darkening coefficients for CoRot and Kepler. Astron. Astrophys. 510, A21 (2010)

    ADS  Google Scholar 

  33. 33

    Hayek, W., Sing, D. K., Pont, F. & Asplund, M. Limb darkening laws for two exoplanet host stars derived from 3D stellar model atmospheres. Comparison with 1D models and HST light curve observations. Astron. Astrophys. 539, A102 (2012)

    ADS  Google Scholar 

  34. 34

    Schwarz, G. Estimating the dimension of a model. Ann. Stat. 6, 461–464 (1978)

    MATH  Google Scholar 

  35. 35

    Markwardt, C. B. Non-linear least squares fitting in IDL with MPFIT. Astron. Soc. Pacif. Conf. Ser . 411, 251–254 (2009)

    ADS  Google Scholar 

  36. 36

    Eastman, J., Gaudi, B. S. & Agol, E. EXOFAST: a fast exoplanetary fitting suite in IDL. Publ. Astron. Soc. Pacif . 125, 83–112 (2013)

    ADS  Google Scholar 

  37. 37

    Gibson, N. P. Reliable inference of exoplanet light-curve parameters using deterministic and stochastic systematics models. Mon. Not. R. Astron. Soc. 445, 3401–3414 (2014)

    ADS  Google Scholar 

  38. 38

    Evans, T. M. et al. A uniform analysis of HD 209458b Spitzer/IRAC lightcurves with Gaussian process models. Mon. Not. R. Astron. Soc. 451, 680–694 (2015)

    ADS  CAS  Google Scholar 

  39. 39

    Fortney, J. J. et al. Transmission spectra of three-dimensional hot Jupiter model atmospheres. Astrophys. J. 709, 1396–1406 (2010)

    ADS  CAS  Google Scholar 

  40. 40

    Lodders, K. Alkali element chemistry in cool dwarf atmospheres. Astrophys. J. 519, 793–801 (1999)

    ADS  CAS  Google Scholar 

  41. 41

    Lodders, K. & Fegley, B. Atmospheric chemistry in giant planets, brown dwarfs, and low-mass dwarf stars. I. Carbon, nitrogen, and oxygen. Icarus 155, 393–424 (2002)

    ADS  CAS  Google Scholar 

  42. 42

    Freedman, R. S., Marley, M. S. & Lodders, K. Line and mean opacities for ultracool dwarfs and extrasolar planets. Astrophys. J. 174 (Supp.), 504–513 (2008)

    ADS  CAS  Google Scholar 

  43. 43

    Visscher, C., Lodders, K. & Fegley, B. Jr. Atmospheric chemistry in giant planets, brown dwarfs, and low-mass dwarf stars. III. Iron, magnesium, and silicon. Astrophys. J. 716, 1060–1075 (2010)

    ADS  CAS  Google Scholar 

  44. 44

    Lecavelier des Etangs, A. et al. Rayleigh scattering in the transit spectrum of HD 189733b. Astron. Astrophys. 481, L83–L86 (2008)

    ADS  CAS  Google Scholar 

  45. 45

    Sing, D. K. et al. Hubble Space Telescope transmission spectroscopy of the exoplanet HD 189733b: high-altitude atmospheric haze in the optical and near-ultraviolet with STIS. Mon. Not. R. Astron. Soc. 416, 1443–1455 (2011)

    ADS  Google Scholar 

  46. 46

    Huitson, C. M. et al. Temperature–pressure profile of the hot Jupiter HD 189733b from HST sodium observations: detection of upper atmospheric heating. Mon. Not. R. Astron. Soc. 422, 2477–2488 (2012)

    ADS  CAS  Google Scholar 

  47. 47

    Vidal-Madjar, A. et al. The upper atmosphere of the exoplanet HD 209458 b revealed by the sodium D lines. Temperature-pressure profile, ionization layer, and thermosphere. Astron. Astrophys. 527, A110 (2011)

    Google Scholar 

  48. 48

    Wyttenbach, A., Ehrenreich, D., Lovis, C., Udry, S. & Pepe, F. Spectrally resolved detection of sodium in the atmosphere of HD 189733b with the HARPS spectrograph. Astron. Astrophys. 577, A62 (2015)

    ADS  Google Scholar 

  49. 49

    Henry, G. W. Techniques for automated high-precision photometry of Sun-like stars. Publ. Astron. Soc. Pacif. 111, 845–860 (1999)

    ADS  Google Scholar 

  50. 50

    Isaacson, H. & Fischer, D. Chromospheric activity and jitter measurements for 2630 stars on the California Planet Search. Astrophys. J. 725, 875–885 (2010)

    ADS  CAS  Google Scholar 

  51. 51

    Knutson, H. A., Howard, A. W. & Isaacson, H. A correlation between stellar activity and hot Jupiter emission spectra. Astrophys. J. 720, 1569–1576 (2010)

    ADS  CAS  Google Scholar 

  52. 52

    Lockwood, G. W. et al. Patterns of photometric and chromospheric variation among sun-like stars: a 20 year perspective. Astrophys. J. 171, 260–303 (2007)

    CAS  Google Scholar 

  53. 53

    Helling, Ch., Woitke, P. & Thi, W.-F. Dust in brown dwarf and extra-solar planets I. Chemical composition and spectral appearance of quasi-static cloud layers. Astron. Astrophys . 485, 547–560 (2008)

    ADS  CAS  Google Scholar 

  54. 54

    Liang, M.-C. et al. On the insignificance of photochemical hydrocarbon aerosols in the atmospheres of close-in extrasolar giant planets. Astrophys. J. 605, L61–L64 (2004)

    ADS  CAS  Google Scholar 

  55. 55

    Moses, J. I. et al. Disequilibrium carbon, oxygen, and nitrogen chemistry in the atmospheres of HD 189733b and HD 209458b. Astrophys. J. 737, 15 (2011)

    ADS  Google Scholar 

Download references

Acknowledgements

This work is based on observations with the NASA/ESA HST, obtained at the Space Telescope Science Institute (STScI) operated by AURA, Inc. This work is also based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement number 336792. D.K.S., F.P. and N.N. acknowledge support from STFC consolidated grant ST/J0016/1. Support for this work was provided by NASA through grants under the HST-GO-12473 programme from the STScI. A.L.E., P.A.W. and A.V.M. acknowledge support from CNES and the French Agence Nationale de la Recherche (ANR), under programme ANR-12-BS05-0012 ‘Exo-Atmos’. P.A.W. and H.W. acknowledge support from the UK Science and Technology Facilities Council (STFC). G.W.H. and M.H.W. acknowledge support from NASA, NSF, Tennessee State University and the State of Tennessee through its Centers of Excellence programme.

Author information

Affiliations

Authors

Contributions

D.K.S. led the data analysis for this project, with contributions from D.D., T.M.E., N.P.G., C.M.H., H.A.K., N.N., H.R.W., S.A., G.E.B. and P.A.W. J.J.F., A.S.B., A.P.S., A.L.E. and T.K. provided atmospheric models. G.W.H. and M.H.W. provided photometric stellar activity monitoring data and J.M.D. provided Spitzer data. D.K.S. wrote the manuscript along with J.J.F., H.R.W, T.K., N.N. and T.M.E. All authors discussed the results and commented on the draft.

Corresponding author

Correspondence to David K. Sing.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 ΔZJ − LM versus ΔZUB − LM.

Black points show the altitude difference between the near-infrared (near-IR) and the mid-infrared (mid-IR) spectral features (Δ ZJ − LM) versus the difference between the blue-optical and mid-infrared (Δ ZUB − LM, see Table 1). Error bars represent the 1σ measurement uncertainties. Purple and grey lines show model trends for hazy and cloud atmospheres, respectively, with increasing Rayleigh scattering haze and grey cloud deck opacity corresponding to 10×, 100× and 1,000× solar. We also show clear-atmosphere models with sub-solar abundances of 0.1×, 0.01× and 0.001× solar (red line).

Extended Data Figure 2 ΔZUB − LM index versus H2O amplitude.

Black points show the altitude difference between the blue-optical and mid-infrared (mid-IR) spectral features (ΔZUB − LM) versus the amplitude of the 1.4-μm H2O absorption spectral feature (see Table 1). Error bars represent the 1σ measurement uncertainties. Purple and grey lines show model trends for hazy and cloud atmospheres, respectively, with increasing Rayleigh scattering haze and grey cloud deck opacity corresponding to 10× , 100× and 1,000× solar. We also show clear-atmosphere models with sub-solar abundances of 0.1× , 0.01× and 0.001× solar (red line).

Extended Data Figure 3 Stellar activity (logRHK) versus ∆ZUB − LM index.

Exoplanets with strong haze signatures have prominent optical slopes with ΔZUB − LM values above 3, while clear atmospheres have ΔZUB − LM indices near zero. The datapoint colours correspond to those in Fig. 1. The red solid line shows the linear regression between the two indices, with 1σ uncertainties (red dashed lines).

Extended Data Figure 4 Theoretical model transmission spectra.

Model spectra17,39 assume a 1,200-K hot Jupiter with a surface gravity of 25 m s−2. Spectra in each panel are compared to a clear, solar-metallicity atmosphere (black line). a, Purple spectra have an added Rayleigh scattering haze corresponding to metallicities of 100× and 1,000× solar. b, Blue and grey spectra have an added grey cloud deck corresponding to 1× and 10× solar. c, Red and green spectra show clear atmospheres with sub-solar abundances of 0.01× and 0.001× solar.

Extended Data Figure 5 Brown dwarf and hot Jupiter pressure–temperature profiles and condensation curves.

Similar to Fig. 2, but alongside the ten hot-Jupiter pressure–temperature profiles we plot the profile of an 1,800-K brown dwarf (green line). The thicker portions of the lines indicate the pressures probed in transmission for the hot Jupiters (plotted in greyscale) and the visible photosphere for the brown dwarf (0.1–10 bar). While a shift in the pressure–temperature profile of a hot Jupiter to hotter and cooler temperatures could dramatically change which condensates may be found in the visible atmosphere, the same would not be true for much shallower brown dwarf pressure–temperature profiles.

Extended Data Table 1 Summary of observations

PowerPoint slides

Source data

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Sing, D., Fortney, J., Nikolov, N. et al. A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion. Nature 529, 59–62 (2016). https://doi.org/10.1038/nature16068

Download citation

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing