JWST MEP - A World Under Spotty Starlight: Detection of CO2 and H2O in the Hot Saturn WASP-52b with JWST NIRSpec G395H

@misc{team2026jwst,
  title = {{JWST MEP - A World Under Spotty Starlight: Detection of CO2 and H2O in the Hot Saturn WASP-52b with JWST NIRSpec G395H}},
  author = {JWST GO 3969 Team and Yanbo Pan and Ryan J. MacDonald and Néstor Espinoza and Bibiana Prinoth and Zafar Rustamkulov and Luis Welbanks and Daniel Kitzmann and Nicolas Crouzet and Anna Walde and Diana Powell and Eva-Maria Ahrer and Adam J. Burgasser and Duncan A. Christie and Wolf Cukier and Carlos Gascón and Måns Holmberg and Thomas Kennedy and Mercedes López-Morales and N. J. Mayne and Dominic Samra and Arjun B. Savel and Maria E. Steinrueck and Christopher P. Wirth},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.21810},
  eprint = {2609.21810},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.21810},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - JWST MEP - A World Under Spotty Starlight: Detection of CO2 and H2O in the Hot Saturn WASP-52b with JWST NIRSpec G395H
AU  - JWST GO 3969 Team
AU  - Yanbo Pan
AU  - Ryan J. MacDonald
AU  - Néstor Espinoza
AU  - Bibiana Prinoth
AU  - Zafar Rustamkulov
AU  - Luis Welbanks
AU  - Daniel Kitzmann
AU  - Nicolas Crouzet
AU  - Anna Walde
AU  - Diana Powell
AU  - Eva-Maria Ahrer
AU  - Adam J. Burgasser
AU  - Duncan A. Christie
AU  - Wolf Cukier
AU  - Carlos Gascón
AU  - Måns Holmberg
AU  - Thomas Kennedy
AU  - Mercedes López-Morales
AU  - N. J. Mayne
AU  - Dominic Samra
AU  - Arjun B. Savel
AU  - Maria E. Steinrueck
AU  - Christopher P. Wirth
PY  - 2026
DA  - 2026/09/18
PB  - arXiv
DO  - 10.48550/arxiv.2609.21810
UR  - https://arxiv.org/abs/2609.21810
AB  - Exoplanets orbiting active stars offer distinct challenges for atmospheric characterization with the JWST. Among such worlds, the hot Saturn WASP-52b (Teq ∼ 1300 K) orbits an active K-dwarf that complicates transmission spectroscopy via stellar contamination. Here, we present the first JWST NIRSpec G395H (2.8-5.2 μm) limb-averaged transmission spectrum of WASP-52b obtained through the JWST Morning/Evening Program (GO-3969), which aims to measure limb asymmetries across a sample of hot giant exoplanets. Our spectrum reveals the first detection of CO2 in WASP-52b's atmosphere (ln B = 54 / >10σ), with a retrieved abundance of log CO2 = -5.09 (+1.09/-1.14), and confirmation of H2O (ln B = 5.9 / ∼3-4σ), with an abundance of log H2O = -3.41 (+1.04/-1.04). We find a steep near-infrared slope that cannot be explained solely by H2O absorption, necessitating unocculted starspots (ln B = 5.7 / ∼3-4σ), though with properties that vary across our data reductions. The shape and amplitude of the molecular bands additionally suggest high-altitude (<10 mbar) inhomogeneous clouds covering ≈40 ± 20% of the terminator (ln B = 1.9 / ∼2.5σ), which provides evidence for the morning-evening terminator differences that are consensus predictions of general circulation models. WASP-52b's atmospheric metallicity can be sub-solar, solar, or super-solar, due to order-of-magnitude uncertainties in the molecular abundances caused by degeneracies between compositions, clouds, and starspots. However, chemical equilibrium retrievals provide a similar statistical fit while favoring a tighter constraint with a super-solar metallicity (M/H = 14.8 (+12.1/-5.9) × solar). These results highlight that chemical detections and aerosol properties may still be recovered for planets orbiting active stars via transmission spectroscopy.
ER  -