TY - JOUR
T1 - A unique hot Jupiter spectral sequence with evidence for compositional diversity
AU - Mansfield, Megan
AU - Line, Michael R.
AU - Bean, Jacob L.
AU - Fortney, Jonathan J.
AU - Parmentier, Vivien
AU - Wiser, Lindsey
AU - Kempton, Eliza M.R.
AU - Gharib-Nezhad, Ehsan
AU - Sing, David K.
AU - López-Morales, Mercedes
AU - Baxter, Claire
AU - Désert, Jean Michel
AU - Swain, Mark R.
AU - Roudier, Gael M.
N1 - Funding Information:
The work was based on observations made with the NASA/ESA Hubble Space Telescope that were obtained from the data archive at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. M.M. acknowledges funding from a NASA FINESST grant. M.R.L. acknowledges funding from NSF AST-165220, and NASA NNX17AB56G. M.R.L. also acknowledges opacity information from R. Lupu. M.R.L., J.L.B. and J.J.F. acknowledge funding for this work from STScI grants GO-13467 and GO-14792. J.J.F. and M.R.L. acknowledge the support of NASA grant 80NSSC19K0446. J.-M.D. acknowledges support from the Amsterdam Academic Alliance Program and from the European Research Council European Union’s Horizon 2020 research and innovation programme (grant no. 679633; Exo-Atmos). This work is part of the research programme VIDI New Frontiers in Exoplanetary Climatology with project number 614.001.601, which is (partly) financed by the Dutch Research Council.
Publisher Copyright:
© 2021, The Author(s), under exclusive licence to Springer Nature Limited.
PY - 2021/12
Y1 - 2021/12
N2 - The emergent spectra of close-in, giant exoplanets (‘hot Jupiters’) are expected to be distinct from those of self-luminous objects with similar effective temperatures because hot Jupiters are primarily heated from above by their host stars rather than internally from the release of energy from their formation1. Theoretical models predict a continuum of dayside spectra for hot Jupiters as a function of irradiation level, with the coolest planets having absorption features in their spectra, intermediate-temperature planets having emission features due to thermal inversions and the hottest planets having blackbody-like spectra due to molecular dissociation and continuum opacity from the H− ion2–4. Absorption and emission features have been detected in the spectra of a number of individual hot Jupiters5,6, and population-level trends have been observed in photometric measurements7–15. However, there has been no unified, population-level study of the thermal emission spectra of hot Jupiters as there has been for cooler brown dwarfs16 and transmission spectra of hot Jupiters17. Here we show that hot Jupiter secondary eclipse spectra centred around a water absorption band at 1.4 μm follow a common trend in water feature strength with temperature. The observed trend is broadly consistent with model predictions for how the thermal structures of solar-composition planets vary with irradiation level, but is inconsistent with the predictions of self-consistent one-dimensional models for internally heated objects. This is particularly the case because models of internally heated objects show absorption features at temperatures above 2,000 K, whereas the observed hot Jupiters show emission features and featureless spectra. Nevertheless, the ensemble of planets exhibits some degree of scatter around the mean trend for solar-composition planets. The spread can be accounted for if the planets have modest variations in metallicity and/or elemental abundance ratios, which is expected from planet formation models18–21.
AB - The emergent spectra of close-in, giant exoplanets (‘hot Jupiters’) are expected to be distinct from those of self-luminous objects with similar effective temperatures because hot Jupiters are primarily heated from above by their host stars rather than internally from the release of energy from their formation1. Theoretical models predict a continuum of dayside spectra for hot Jupiters as a function of irradiation level, with the coolest planets having absorption features in their spectra, intermediate-temperature planets having emission features due to thermal inversions and the hottest planets having blackbody-like spectra due to molecular dissociation and continuum opacity from the H− ion2–4. Absorption and emission features have been detected in the spectra of a number of individual hot Jupiters5,6, and population-level trends have been observed in photometric measurements7–15. However, there has been no unified, population-level study of the thermal emission spectra of hot Jupiters as there has been for cooler brown dwarfs16 and transmission spectra of hot Jupiters17. Here we show that hot Jupiter secondary eclipse spectra centred around a water absorption band at 1.4 μm follow a common trend in water feature strength with temperature. The observed trend is broadly consistent with model predictions for how the thermal structures of solar-composition planets vary with irradiation level, but is inconsistent with the predictions of self-consistent one-dimensional models for internally heated objects. This is particularly the case because models of internally heated objects show absorption features at temperatures above 2,000 K, whereas the observed hot Jupiters show emission features and featureless spectra. Nevertheless, the ensemble of planets exhibits some degree of scatter around the mean trend for solar-composition planets. The spread can be accounted for if the planets have modest variations in metallicity and/or elemental abundance ratios, which is expected from planet formation models18–21.
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U2 - 10.1038/s41550-021-01455-4
DO - 10.1038/s41550-021-01455-4
M3 - Article
AN - SCOPUS:85117445665
SN - 2397-3366
VL - 5
SP - 1224
EP - 1232
JO - Nature Astronomy
JF - Nature Astronomy
IS - 12
ER -