JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b

Abstract Theoretical studies have suggested using planetary infrared excess (PIE) to detect and characterize the thermal emission of transiting and nontransiting exoplanets, although the PIE technique requires empirical validation. Here, we apply the PIE technique to a combination of JWST NIRSpec G395H transit and eclipse measurements of WASP-17b, a hot Jupiter orbiting an F-type star, obtained consecutively (one-half of the orbital period or 1.8 days apart) as part of the JWST-TST program to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy. Using the in-eclipse measured stellar spectrum to circumvent the need for ultraprecise stellar models, we extract the first JWST nightside emission spectrum of WASP-17b using only transit and eclipse data, thereby performing a controlled test of the PIE technique. From the WASP-17b nightside spectrum, we measure a nightside equilibrium temperature of 1006 ± 276 K and find tentative evidence for nightside SO 2 absorption ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ln</mml:mi> <mml:mi>B</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1.4</mml:mn> </mml:math> ). In context with the dayside, the temperature of the nightside is consistent with: (1) previous eclipse mapping findings that suggest relatively inefficient day–night heat transport; and (2) a nonzero bond albedo of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0.4</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . SO 2 on the nightside, if confirmed, would represent the first direct evidence for transport-induced chemistry, matching previous model predictions and opening a new door onto the 3D nature of giant exoplanets. Our results suggest that PIE is feasible with JWST/NIRSpec for two epochs separated in time by significantly less than the rotation period of the host star.

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Publication Details

Journal
The Astrophysical Journal Letters
Published
2025-11-11
DOI
https://doi.org/10.3847/2041-8213/ae17ae
Citations
1
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
1.15
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article

JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b

Jeff A. Valenti, Roeland P. van der Marel, Jayesh Goyal, Sarah M. Hörst et al.
1 citations
The Astrophysical Journal Letters
Stellar, planetary, and galactic studies
1.15
article

JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b

Jeff A. Valenti, Roeland P. van der Marel, Jayesh Goyal, Sarah M. Hörst, Dana R. Louie, Amélie Gressier, Jingcheng Huang, Kevin B. Stevenson, Sarah Peacock, Nikole K. Lewis, Natalie H. Allen, Elijah Mullens, Marshall D. Perrin, Jacob Lustig‐Yaeger, Edward W. Schwieterman, Ryan C. Challener, L. C. Mayorga, Shang‐Min Tsai, Zifan Lin, Daniel T. Valentine, Lili Alderson, Avi M. Mandell, Kristin S. Sotzen, Thomas J. Fauchez, C. M. Mountain, Hannah R. Wakeford, Ana Glidden
article en
1 citations

Abstract

Abstract Theoretical studies have suggested using planetary infrared excess (PIE) to detect and characterize the thermal emission of transiting and nontransiting exoplanets, although the PIE technique requires empirical validation. Here, we apply the PIE technique to a combination of JWST NIRSpec G395H transit and eclipse measurements of WASP-17b, a hot Jupiter orbiting an F-type star, obtained consecutively (one-half of the orbital period or 1.8 days apart) as part of the JWST-TST program to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy. Using the in-eclipse measured stellar spectrum to circumvent the need for ultraprecise stellar models, we extract the first JWST nightside emission spectrum of WASP-17b using only transit and eclipse data, thereby performing a controlled test of the PIE technique. From the WASP-17b nightside spectrum, we measure a nightside equilibrium temperature of 1006 ± 276 K and find tentative evidence for nightside SO 2 absorption ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ln</mml:mi> <mml:mi>B</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1.4</mml:mn> </mml:math> ). In context with the dayside, the temperature of the nightside is consistent with: (1) previous eclipse mapping findings that suggest relatively inefficient day–night heat transport; and (2) a nonzero bond albedo of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0.4</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . SO 2 on the nightside, if confirmed, would represent the first direct evidence for transport-induced chemistry, matching previous model predictions and opening a new door onto the 3D nature of giant exoplanets. Our results suggest that PIE is feasible with JWST/NIRSpec for two epochs separated in time by significantly less than the rotation period of the host star.

The Astrophysical Journal LettersVol. 994(1)
University of California, Riverside (US), Space Telescope Science Institute (US), Planetary Science Institute (US), Goddard Space Flight Center (US), Institute of Astronomy and Astrophysics, Academia Sinica (TW), Association of Universities for Research in Astronomy (US), Johns Hopkins University (US), National Institute of Science Education and Research (IN), University of America (US), American University (US), Washington University in St. Louis (US), Cornell University (US), Johns Hopkins Medicine (US), NASA Exoplanet Science Institute (US), Johns Hopkins University Applied Physics Laboratory (US), University of Bristol (GB), Université Bourgogne Franche-Comté (FR), Massachusetts Institute of Technology (US), University of Maryland, Baltimore County (US)
Openalex Percentile: Top 15%
Stellar, planetary, and galactic studies
1.15
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