Clouds form on the hot Saturn JWST ERO target WASP-96b

Dominic Samra; Christiane Helling; Katy Chubb; Michiel Min; Ludmila Carone; Aaron Schneider

doi:10.1051/0004-6361/202244939

Clouds form on the hot Saturn JWST ERO target WASP-96b

Dominic Samra^*, Christiane Helling, Katy Chubb, Michiel Min, Ludmila Carone, Aaron Schneider

^*Corresponding author for this work

School of Physics and Astronomy

Research output: Contribution to journal › Article › peer-review

Abstract

Context. WASP-96b is a hot Saturn exoplanet, with an equilibrium temperature of ≈ 1300 K. This is well within the regime of thermodynamically expected extensive cloud formation. Prior observations with Hubble/WFC3, Spitzer/IRAC, and VLT/FORS2 have been combined into a single spectrum for which retrievals suggest a cold but cloud-free atmosphere. Recently, the planet was observed with the James Webb Space Telescope (JWST) as part of the Early Release Observations (ERO).

Aims. The formation of clouds in the atmosphere of exoplanet WASP-96b is explored.

Methods. One-dimensional profiles were extracted from the 3D GCM expeRT/MITgcm results and used as input for a kinetic, non-equilibrium model to study the formation of mineral cloud particles of mixed composition. The ARCiS retrieval framework was applied to the pre-JWST WASP-96b transit spectrum to investigate the apparent contradiction between cloudy models and assumed cloud-free transit spectrum.

Results. Clouds are predicted to be ubiquitous throughout the atmosphere of WASP-96b. Silicate materials contribute between 40% and 90% cloud particle volume, which means that metal oxides also contribute with up to 40% cloud particle volume in the low-pressure regimes that affect spectra. We explore how these cloudy models match currently available transit spectra. Reduced vertical mixing acts to settle clouds to deeper in the atmosphere, and an increased cloud particle porosity reduces the opacity of clouds in the near-IR and optical region. These two effects allow for clearer molecular features to be observed while still allowing clouds to be in the atmosphere.

Conclusions. The atmosphere of WASP-96b is unlikely to be cloud free. Retrievals of HST, Spitzer, and VLT spectra also show that multiple cloudy solutions reproduce the data. JWST observations will be affected by clouds, where the cloud top pressure varies by an order of magnitude within even the NIRISS wavelength range. The long-wavelength end of NIRSpec and the short-wavelength end of MIRI may probe atmospheric asymmetries between the limbs of the terminator on WASP-96b.

Original language	English
Article number	A142
Number of pages	17
Journal	Astronomy & Astrophysics
Volume	669
Early online date	25 Jan 2023
DOIs	https://doi.org/10.1051/0004-6361/202244939
Publication status	Published - 25 Jan 2023

Keywords

Planets and satellites: individual: WASP-96b
Planets and satellites: gaseous planets
Planets and satellites: fundamental parameters
Planets and satellites: atmospheres

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10.1051/0004-6361/202244939Licence: CC BY

Samra_2023_AA_Clouds-form_CC
Copyright © The Authors 2023. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Final published version, 4.25 MBLicence: CC BY

http://arxiv.org/abs/2211.00633

H2020 MSCA ITN EJD 2019: H2020 MSCA ITN EJD 2019 CHAMELEON
Helling, C. (PI)
European Commission
1/06/20 → 31/05/24
Project: Standard

Cite this

@article{01ab981a1b8b4001950d278df68e68ea,

title = "Clouds form on the hot Saturn JWST ERO target WASP-96b",

abstract = "Context. WASP-96b is a hot Saturn exoplanet, with an equilibrium temperature of ≈ 1300 K. This is well within the regime of thermodynamically expected extensive cloud formation. Prior observations with Hubble/WFC3, Spitzer/IRAC, and VLT/FORS2 have been combined into a single spectrum for which retrievals suggest a cold but cloud-free atmosphere. Recently, the planet was observed with the James Webb Space Telescope (JWST) as part of the Early Release Observations (ERO). Aims. The formation of clouds in the atmosphere of exoplanet WASP-96b is explored. Methods. One-dimensional profiles were extracted from the 3D GCM expeRT/MITgcm results and used as input for a kinetic, non-equilibrium model to study the formation of mineral cloud particles of mixed composition. The ARCiS retrieval framework was applied to the pre-JWST WASP-96b transit spectrum to investigate the apparent contradiction between cloudy models and assumed cloud-free transit spectrum. Results. Clouds are predicted to be ubiquitous throughout the atmosphere of WASP-96b. Silicate materials contribute between 40% and 90% cloud particle volume, which means that metal oxides also contribute with up to 40% cloud particle volume in the low-pressure regimes that affect spectra. We explore how these cloudy models match currently available transit spectra. Reduced vertical mixing acts to settle clouds to deeper in the atmosphere, and an increased cloud particle porosity reduces the opacity of clouds in the near-IR and optical region. These two effects allow for clearer molecular features to be observed while still allowing clouds to be in the atmosphere. Conclusions. The atmosphere of WASP-96b is unlikely to be cloud free. Retrievals of HST, Spitzer, and VLT spectra also show that multiple cloudy solutions reproduce the data. JWST observations will be affected by clouds, where the cloud top pressure varies by an order of magnitude within even the NIRISS wavelength range. The long-wavelength end of NIRSpec and the short-wavelength end of MIRI may probe atmospheric asymmetries between the limbs of the terminator on WASP-96b.",

keywords = "Planets and satellites: individual: WASP-96b, Planets and satellites: gaseous planets, Planets and satellites: fundamental parameters, Planets and satellites: atmospheres",

author = "Dominic Samra and Christiane Helling and Katy Chubb and Michiel Min and Ludmila Carone and Aaron Schneider",

note = "Funding: Ch.H., M.M., L.C., and A.D.S. acknowledge funding from the European Union H2020-MSCA-ITN-2019 under Grant Agreement no. 860470 (CHAMELEON). K.L.C. acknowledges funding from STFC, under project number ST/V000861/1. D.S. acknowledges financial support from the Austrian Academy of Science.",

year = "2023",

month = jan,

day = "25",

doi = "10.1051/0004-6361/202244939",

language = "English",

volume = "669",

journal = "Astronomy & Astrophysics",

issn = "0004-6361",

publisher = "EDP SCIENCES S A",

}

TY - JOUR

T1 - Clouds form on the hot Saturn JWST ERO target WASP-96b

AU - Samra, Dominic

AU - Helling, Christiane

AU - Chubb, Katy

AU - Min, Michiel

AU - Carone, Ludmila

AU - Schneider, Aaron

N1 - Funding: Ch.H., M.M., L.C., and A.D.S. acknowledge funding from the European Union H2020-MSCA-ITN-2019 under Grant Agreement no. 860470 (CHAMELEON). K.L.C. acknowledges funding from STFC, under project number ST/V000861/1. D.S. acknowledges financial support from the Austrian Academy of Science.

PY - 2023/1/25

Y1 - 2023/1/25

N2 - Context. WASP-96b is a hot Saturn exoplanet, with an equilibrium temperature of ≈ 1300 K. This is well within the regime of thermodynamically expected extensive cloud formation. Prior observations with Hubble/WFC3, Spitzer/IRAC, and VLT/FORS2 have been combined into a single spectrum for which retrievals suggest a cold but cloud-free atmosphere. Recently, the planet was observed with the James Webb Space Telescope (JWST) as part of the Early Release Observations (ERO). Aims. The formation of clouds in the atmosphere of exoplanet WASP-96b is explored. Methods. One-dimensional profiles were extracted from the 3D GCM expeRT/MITgcm results and used as input for a kinetic, non-equilibrium model to study the formation of mineral cloud particles of mixed composition. The ARCiS retrieval framework was applied to the pre-JWST WASP-96b transit spectrum to investigate the apparent contradiction between cloudy models and assumed cloud-free transit spectrum. Results. Clouds are predicted to be ubiquitous throughout the atmosphere of WASP-96b. Silicate materials contribute between 40% and 90% cloud particle volume, which means that metal oxides also contribute with up to 40% cloud particle volume in the low-pressure regimes that affect spectra. We explore how these cloudy models match currently available transit spectra. Reduced vertical mixing acts to settle clouds to deeper in the atmosphere, and an increased cloud particle porosity reduces the opacity of clouds in the near-IR and optical region. These two effects allow for clearer molecular features to be observed while still allowing clouds to be in the atmosphere. Conclusions. The atmosphere of WASP-96b is unlikely to be cloud free. Retrievals of HST, Spitzer, and VLT spectra also show that multiple cloudy solutions reproduce the data. JWST observations will be affected by clouds, where the cloud top pressure varies by an order of magnitude within even the NIRISS wavelength range. The long-wavelength end of NIRSpec and the short-wavelength end of MIRI may probe atmospheric asymmetries between the limbs of the terminator on WASP-96b.

AB - Context. WASP-96b is a hot Saturn exoplanet, with an equilibrium temperature of ≈ 1300 K. This is well within the regime of thermodynamically expected extensive cloud formation. Prior observations with Hubble/WFC3, Spitzer/IRAC, and VLT/FORS2 have been combined into a single spectrum for which retrievals suggest a cold but cloud-free atmosphere. Recently, the planet was observed with the James Webb Space Telescope (JWST) as part of the Early Release Observations (ERO). Aims. The formation of clouds in the atmosphere of exoplanet WASP-96b is explored. Methods. One-dimensional profiles were extracted from the 3D GCM expeRT/MITgcm results and used as input for a kinetic, non-equilibrium model to study the formation of mineral cloud particles of mixed composition. The ARCiS retrieval framework was applied to the pre-JWST WASP-96b transit spectrum to investigate the apparent contradiction between cloudy models and assumed cloud-free transit spectrum. Results. Clouds are predicted to be ubiquitous throughout the atmosphere of WASP-96b. Silicate materials contribute between 40% and 90% cloud particle volume, which means that metal oxides also contribute with up to 40% cloud particle volume in the low-pressure regimes that affect spectra. We explore how these cloudy models match currently available transit spectra. Reduced vertical mixing acts to settle clouds to deeper in the atmosphere, and an increased cloud particle porosity reduces the opacity of clouds in the near-IR and optical region. These two effects allow for clearer molecular features to be observed while still allowing clouds to be in the atmosphere. Conclusions. The atmosphere of WASP-96b is unlikely to be cloud free. Retrievals of HST, Spitzer, and VLT spectra also show that multiple cloudy solutions reproduce the data. JWST observations will be affected by clouds, where the cloud top pressure varies by an order of magnitude within even the NIRISS wavelength range. The long-wavelength end of NIRSpec and the short-wavelength end of MIRI may probe atmospheric asymmetries between the limbs of the terminator on WASP-96b.

KW - Planets and satellites: individual: WASP-96b

KW - Planets and satellites: gaseous planets

KW - Planets and satellites: fundamental parameters

KW - Planets and satellites: atmospheres

U2 - 10.1051/0004-6361/202244939

DO - 10.1051/0004-6361/202244939

M3 - Article

SN - 0004-6361

VL - 669

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

M1 - A142

ER -

Clouds form on the hot Saturn JWST ERO target WASP-96b

Abstract

Keywords

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H2020 MSCA ITN EJD 2019: H2020 MSCA ITN EJD 2019 CHAMELEON

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