Science of the early release of exoplanet WASP-39b with JWST NIRCam

Transmission spectrum measured against the forward atmospheric model grids. Top: The best fit for each model grid (represented by solid colored lines; PICASO 3.0, ATMO, PHOENIX), corresponds to the planetary spectrum (Eureka reduction!) with χ ν 2 ≤ 1.22. All individual best fits prefer at least solar metallicity and substantial cloud cover. Also represented by a gray dotted line is an atmospheric model of solar metallicity, stellar C/O ratio, demonstrating the lack of methane uptake observed in the spectrum. Because we can set an upper limit on the abundance of CH, the preferred C/O ratio found by the model grids is 4 substellar. Bottom: Residuals of each best fit, represented by the model spectrum subtracted from the reduced spectrum and divided by the transit depth uncertainty. The residuals show wavelength-dependent correlations, the origin of which is unknown and left for future study. — astro-ph.EP

Measuring metallicity and the carbon-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step in limiting the dominant chemical processes at work and, if in equilibrium, revealing the history of the formation of planets.

Transmission spectroscopy provides the necessary means by limiting the abundances of oxygenated and carbonaceous species; however, this requires wide wavelength coverage, moderate spectral resolution, and high precision which together are not achievable with previous observatories.

Now that JWST has begun its scientific operations, we are able to observe exoplanets at previously unexplored wavelengths and spectral resolutions. Here, we report time-series observations of the transiting exoplanet WASP-39b using JWST’s near-infrared camera (NIRCam). The long-wavelength spectroscopic and short-wavelength photometric light curves span from 2.0 to 4.0 μm, exhibit minimal systematics, and reveal well-defined molecular absorption features in the spectrum of the planet. Specifically, we detect gaseous H2O in the atmosphere and place an upper limit on the abundance of CH4.

The otherwise prominent CO2 feature at 2.8 μm is largely masked by H2O. The best-fitting chemical equilibrium models favor an atmospheric metallicity of 1-100× solar (i.e. enrichment in elements heavier than helium relative to the Sun) and a carbon-oxygen ratio (C /O) substellar. The inferred high metallicity and low C/O ratio may indicate significant accretion of solid materials during planet formation or disequilibrium processes in the upper atmosphere.

Eva-Maria Ahrer, Kevin B. Stevenson, Megan Mansfield, Sarah E. Moran, Jonathan Brande, Giuseppe Morello, Catriona A. Murray, Nikolay K. Nikolov, Dominique JM Petit dit de la Roche, Everett Schlawin, Peter J. Wheatley, Sebastian Zieba, Natasha E. Batalha, Mario Damiano, Jayesh M Goyal, Monika Lendl, Joshua D. Lothringer, Sagnick Mukherjee, Kazumasa Ohno, Natalie M. Batalha, Matthew P. Battley, Jacob L. Bean, Thomas G. Beatty, Björn Benneke, Zachory K. Berta-Thompson, Aarynn L. Carter, Patricio E. Cubillos, Tansu Daylan, Néstor Espinoza, Peter Gao, Neale P. Gibson, Samuel Gill, Joseph Harrington, Renyu Hu, Laura Kreidberg, Nikole K. Lewis, Michael R. Line, Mercedes López-Morales, Vivien Parmentier, Diana K. Powell, David K. Sing, Shang-Min Tsai, Hannah R Wakeford, Luis Welbanks, Munazza K. Alam, Lili Alderson, Natalie H. Allen, David R Anderson, Joanna K. Barstow, Daniel Bayliss, Taylor J. Bell, Jasmina Blecic, Edward M. Bryant, Matthew R. Burleigh, Ludmila Carone, SL Casewell, Quentin C hangeat, Katy L. Chubb, Ian JM Crossfield, Nicolas Crouzet, Leen Decin, Jean-Michel Désert, Adina D. Feinstein, Laura Flagg, Jonathan J. Fortney, John E. Gizis, Kevin Heng, Nicolas Iro, Eliza M.- R Kempton, Sarah Kendrew, James Kirk, Heather A. Knutson, Thaddeus D. Komacek, Pierre-Olivier Lagage, Jérémy Leconte, Jacob Lustig-Yaeger, Ryan J. MacDonald, Luigi Mancini, EM May, NJ Mayne, Yamila Miguel, Thomas Mikal -Evans, Karan Molaverdikhani, Enric Palle, Caroline Piaulet, Benjamin V. Rackham, Seth Redfield, Laura K. Rogers, Pierre-Alexis Roy, Zafar Rustamkulov, Evgenya L. Shkolnik, Kristin S. Sotzen, Jake Taylor, P. Tremblin , Gregory S. Tucker, Jake D. Turner, Miguel de Val-Borro, Olivia Venot, Xi Zhang

Comments: 35 pages, 13 figures, 3 tables, Nature, accepted
Subjects: Terrestrial and planetary astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2211.10489 [astro-ph.EP] (or arXiv:2211.10489v1 [astro-ph.EP] for this version)
Submission history
From: Eva-Maria Ahrer
[v1] Fri, Nov 18, 2022 7:57:14 PM UTC (4,186 KB)

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