{
  "abstract": "As part of the JWST Hot Rocks Survey, we analyzed a JWST/MIRI F1500W secondary-eclipse observation of GJ 357 b, a rocky exoplanet orbiting a nearby M dwarf. We also performed a new global analysis of the GJ 357 system, combining TESS photometry, a JWST/NIRSpec transit observation, the MIRI secondary eclipse, radial velocities, and Gaia parallax measurements to obtain a self-consistent set of stellar and planetary parameters. We measure an occultation depth of $200.5 \\pm 12.7,\\mathrm{ppm}$, corresponding to a dayside brightness temperature at $15,μ\\mathrm{m}$ of $T_{\\mathrm{b},15,μ\\mathrm{m}}=923^{+39}_{-38},\\mathrm{K}$. The inferred brightness temperature substantially exceeds the zero-Bond-albedo, no-redistribution, disk-integrated bolometric dayside reference temperature of $686 \\pm 14,\\mathrm{K}$. The measured eclipse depth differs from the tested zero-albedo, grey airless-surface model by $5.2σ$ and is also inconsistent with the high-mean-molecular-weight atmospheric models considered here, including pure CO$_2$, pure H$_2$O, and N$_2$ with 100 ppm CO$_2$. Possible explanations for the excess emission in the MIRI/F1500W band include wavelength-dependent surface emissivity, localized hot regions, or atmospheric temperature structures and opacity sources not included in the tested models. Follow-up mid-infrared eclipse spectroscopy would constrain the shape of the dayside emission spectrum and help test the proposed surface and atmospheric explanations.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.30552",
  "author_total": 18,
  "authors": [
    {
      "name": "Merlin Zgraggen"
    },
    {
      "name": "Brice-Olivier Demory"
    },
    {
      "name": "Hannah Diamond-Lowe"
    },
    {
      "name": "João M. Mendonça"
    },
    {
      "name": "Erik Meier Valdés"
    },
    {
      "name": "Mark Fortune"
    },
    {
      "name": "Kathryn D. Jones"
    },
    {
      "name": "Daniel Kitzmann"
    },
    {
      "name": "Millie Smith"
    },
    {
      "name": "Natalie H. Allen"
    },
    {
      "name": "Prune C. August"
    },
    {
      "name": "Amélie Gressier"
    },
    {
      "name": "Måns Holmberg"
    },
    {
      "name": "Jegug Ih"
    },
    {
      "name": "Lars A. Buchhave"
    },
    {
      "name": "Néstor Espinoza"
    },
    {
      "name": "Neale P. Gibson"
    },
    {
      "name": "Kevin Heng"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/1m7e8hrtnr12a.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.30552",
  "fulltext_url": null,
  "id": "1m7e8hrtnr12a",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.30552",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.EP"
    ],
    [
      "openalex",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7214662957",
  "pdf_url": "https://arxiv.org/pdf/2609.30552",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-24",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/1m7e8hrtnr12a.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:52Z",
      "native_id": "2609.30552",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.30552"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "Hot Rocks Survey VI: An anomalously hot dayside for the rocky planet GJ 357 b",
  "title_text": "Hot Rocks Survey VI: An anomalously hot dayside for the rocky planet GJ 357 b",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:52Z",
  "url": "https://research.draconitic.com/paper/1m7e8hrtnr12a",
  "venue": "arXiv",
  "versions": []
}