{
  "abstract": "Exoplanets orbiting active stars offer distinct challenges for atmospheric characterization with the JWST. Among such worlds, the hot Saturn WASP-52b (Teq $\\sim$ 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 $μ$m) 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 / >10$σ$), with a retrieved abundance of log CO2 = -5.09 (+1.09/-1.14), and confirmation of H2O (ln B = 5.9 / $\\sim$3-4$σ$), 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 / $\\sim$3-4$σ$), 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 $\\approx$40 $\\pm$ 20% of the terminator (ln B = 1.9 / $\\sim$2.5$σ$), 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) $\\times$ solar). These results highlight that chemical detections and aerosol properties may still be recovered for planets orbiting active stars via transmission spectroscopy.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.21810",
  "author_total": 24,
  "authors": [
    {
      "name": "JWST GO 3969 Team"
    },
    {
      "name": "Yanbo Pan"
    },
    {
      "name": "Ryan J. MacDonald"
    },
    {
      "name": "Néstor Espinoza"
    },
    {
      "name": "Bibiana Prinoth"
    },
    {
      "name": "Zafar Rustamkulov"
    },
    {
      "name": "Luis Welbanks"
    },
    {
      "name": "Daniel Kitzmann"
    },
    {
      "name": "Nicolas Crouzet"
    },
    {
      "name": "Anna Walde"
    },
    {
      "name": "Diana Powell"
    },
    {
      "name": "Eva-Maria Ahrer"
    },
    {
      "name": "Adam J. Burgasser"
    },
    {
      "name": "Duncan A. Christie"
    },
    {
      "name": "Wolf Cukier"
    },
    {
      "name": "Carlos Gascón"
    },
    {
      "name": "Måns Holmberg"
    },
    {
      "name": "Thomas Kennedy"
    },
    {
      "name": "Mercedes López-Morales"
    },
    {
      "name": "N. J. Mayne"
    },
    {
      "name": "Dominic Samra"
    },
    {
      "name": "Arjun B. Savel"
    },
    {
      "name": "Maria E. Steinrueck"
    },
    {
      "name": "Christopher P. Wirth"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fe9cqhgvv0cz5.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.21810",
  "fulltext_url": null,
  "id": "fe9cqhgvv0cz5",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.21810",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.EP"
    ],
    [
      "arxiv",
      "astro-ph.SR"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.21810",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-18",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fe9cqhgvv0cz5.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:23:03Z",
      "native_id": "2609.21810",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.21810"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.SR",
      "subfield": "stellar"
    }
  ],
  "title": "JWST MEP - A World Under Spotty Starlight: Detection of CO2 and H2O in the Hot Saturn WASP-52b with JWST NIRSpec G395H",
  "title_text": "JWST MEP - A World Under Spotty Starlight: Detection of CO2 and H2O in the Hot Saturn WASP-52b with JWST NIRSpec G395H",
  "type": "preprint",
  "updated_at": "2026-10-30T12:23:03Z",
  "url": "https://research.draconitic.com/paper/fe9cqhgvv0cz5",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.3847/1538-3881/ae9cbc",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}