JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b
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| Format: | Preprint |
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2025
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| author | Lustig-Yaeger, Jacob Sotzen, Kristin S. Stevenson, Kevin B. Tsai, Shang-Min Challener, Ryan C. Goyal, Jayesh Lewis, Nikole K. Louie, Dana R. Mayorga, L. C. Valentine, Daniel Wakeford, Hannah R. Alderson, Lili Allen, Natalie H. Fauchez, Thomas J. Glidden, Ana Gressier, Amélie Hörst, Sarah M. Huang, Jingcheng Lin, Zifan Mandell, Avi M. Mullens, Elijah Peacock, Sarah Schwieterman, Edward W. Valenti, Jeff A. Mountain, C. Matt Perrin, Marshall van der Marel, Roeland P. |
| author_facet | Lustig-Yaeger, Jacob Sotzen, Kristin S. Stevenson, Kevin B. Tsai, Shang-Min Challener, Ryan C. Goyal, Jayesh Lewis, Nikole K. Louie, Dana R. Mayorga, L. C. Valentine, Daniel Wakeford, Hannah R. Alderson, Lili Allen, Natalie H. Fauchez, Thomas J. Glidden, Ana Gressier, Amélie Hörst, Sarah M. Huang, Jingcheng Lin, Zifan Mandell, Avi M. Mullens, Elijah Peacock, Sarah Schwieterman, Edward W. Valenti, Jeff A. Mountain, C. Matt Perrin, Marshall van der Marel, Roeland P. |
| contents | Theoretical studies have suggested using planetary infrared excess (PIE) to detect and characterize the thermal emission of transiting and non-transiting exoplanets, however 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 (0.5 phase or 1.8 days apart) as part of the JWST-TST program to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS). Using the in-eclipse measured stellar spectrum to circumvent the need for ultra-precise 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 $1005 \pm 256$ K and find tentative evidence for nightside SO2 absorption ($\ln B = 1.45$, $2.3σ$). 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 non-zero bond albedo of $0.42^{+0.06}_{-0.10}$. SO2 on the nightside, if confirmed, would represent the first direct evidence for transport-induced chemistry, matching previous model predictions, and opening a new door into 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_06169 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b Lustig-Yaeger, Jacob Sotzen, Kristin S. Stevenson, Kevin B. Tsai, Shang-Min Challener, Ryan C. Goyal, Jayesh Lewis, Nikole K. Louie, Dana R. Mayorga, L. C. Valentine, Daniel Wakeford, Hannah R. Alderson, Lili Allen, Natalie H. Fauchez, Thomas J. Glidden, Ana Gressier, Amélie Hörst, Sarah M. Huang, Jingcheng Lin, Zifan Mandell, Avi M. Mullens, Elijah Peacock, Sarah Schwieterman, Edward W. Valenti, Jeff A. Mountain, C. Matt Perrin, Marshall van der Marel, Roeland P. Earth and Planetary Astrophysics Theoretical studies have suggested using planetary infrared excess (PIE) to detect and characterize the thermal emission of transiting and non-transiting exoplanets, however 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 (0.5 phase or 1.8 days apart) as part of the JWST-TST program to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS). Using the in-eclipse measured stellar spectrum to circumvent the need for ultra-precise 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 $1005 \pm 256$ K and find tentative evidence for nightside SO2 absorption ($\ln B = 1.45$, $2.3σ$). 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 non-zero bond albedo of $0.42^{+0.06}_{-0.10}$. SO2 on the nightside, if confirmed, would represent the first direct evidence for transport-induced chemistry, matching previous model predictions, and opening a new door into 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. |
| title | JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2510.06169 |