UV absorption by silicate cloud precursors in ultra-hot Jupiter WASP-178b
Abstract
Aerosols have been found to be nearly ubiquitous in substellar atmospheres1,2,3. The precise temperature at which these aerosols begin to form in exoplanets has yet to be observationally constrained. Theoretical models and observations of muted spectral features indicate that silicate clouds play an important role in exoplanets between at least 950 and 2,100 K (ref. 4). Some giant planets, however, are thought to be hot enough to avoid condensation altogether5,6. Here we report the near-ultraviolet transmission spectrum of the ultra-hot Jupiter WASP-178b (approximately 2,450 K), which exhibits substantial absorption. Bayesian retrievals indicate the presence of gaseous refractory species containing silicon and magnesium, which are the precursors to condensate clouds at lower temperatures. SiO, in particular, has not previously, to our knowledge, been detected in exoplanets, but the presence of SiO in WASP-178b is consistent with theoretical expectations as the dominant Si-bearing species at high temperatures. These observations allow us to re-interpret previous observations of HAT-P-41b and WASP-121b that did not consider SiO, to suggest that silicate cloud formation begins on exoplanets with equilibrium temperatures between 1,950 and 2,450 K.
Additional Information
© 2022 Nature Publishing Group. Received 20 September 2021; Accepted 24 January 2022; Published 06 April 2022. We thank the UV-SCOPE team for relevant discussions. We thank T. Barman for the use of the computing resources used in the calculation of the atmospheric retrievals. Support for this work was provided by NASA through grant number HST-GO-16086 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. This research has made use of the NASA Astrophysics Data System and the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Data availability: The raw data from this study, HST Program 16068, is publicly available via the Space Science Telescope Institute's Mikulski Archive for Space Telescopes (https://archive.stsci.edu/). Code availability: The raw data was reduced with the available STScI CALWF3 pipeline and spectra were extracted with the public IRAF apall routines. The light curve fitting used custom routines that we opt not to make public due to undocumented intricacies. Model and retrievals were generated using PHOENIX, which is a proprietary code but described in many publications, for example, refs. 66,67. These authors contributed equally: Joshua D. Lothringer, David K. Sing. Contributions: J.D.L. and D.K.S. contributed equally to this work. J.D.L. led the observing proposal with the assistance of D.K.S., Z.R., H.R.W., K.B.S., N.N. and P.L. J.D.L. also led the retrieval analysis. D.K.S. led the data analysis with contributions from Z.R., H.R.W., J.J.S. and A.T.W. All authors discussed the data analysis and interpretation and commented on the manuscript. The authors declare no competing interests. Peer review information: Nature thanks Tad Komacek and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.Attached Files
Accepted Version - 2204.03639.pdf
Supplemental Material - 41586_2022_4453_Fig10_ESM.webp
Supplemental Material - 41586_2022_4453_Fig11_ESM.webp
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Supplemental Material - 41586_2022_4453_Tab1_ESM.jpg
Supplemental Material - 41586_2022_4453_Tab2_ESM.jpg
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Additional details
- Eprint ID
- 114238
- DOI
- 10.1038/s41586-022-04453-2
- Resolver ID
- CaltechAUTHORS:20220412-364822400
- HST-GO-16086
- NASA
- NAS 5-26555
- NASA
- Created
-
2022-04-12Created from EPrint's datestamp field
- Updated
-
2022-04-12Created from EPrint's last_modified field