{
  "abstract": "Rocky planets evolve through the exchange of volatiles between their interiors and atmospheres, an interplay still poorly constrained by observations. Remarkably, highly irradiated ultrashort-period (USP) exoplanets may offer a window into this exchange -- some retain low bulk densities compatible with volatile-rich envelopes surrounding rocky interiors, indicating possible secondary atmospheres. TOI-561 b is a prime example, with a bulk density of $4.3\\pm0.4$ g cm$^{-3}$ and recent JWST observations favoring a thick volatile atmosphere overlying a dayside magma ocean. Here, we investigate the evolutionary pathways allowing TOI-561 b to retain a substantial atmosphere over gigayears using the PROTEUS coupled interior--atmosphere framework. We explore different core radius fractions, Bond albedos, atmospheric escape efficiencies, mantle redox states, and initial C--H--O--N--S volatile inventories, under in situ evolution and late inward migration. Over half of our simulations leave a bare interior too dense to match observations. Successful cases favor a volatile-rich origin ($\\lesssim200$ Earth oceans of hydrogen, S/H $\\le10$, and N/H $\\le1$), an oxidized mantle ($f$O$_2 \\gtrsim \\mathrm{IW}+4$), a small iron core ($\\le 0.40$ for the core radius fraction), and low escape efficiency ($ε\\lesssim 10^{-3}$) in the hydrodynamic escape regime. At present, TOI-561 b is consistent with a global magma ocean beneath a thick (surface pressure $\\approx 10^{3}$--$10^{4}$ bar), high mean molecular weight atmosphere ($38$--$60$ g mol$^{-1}$). Two archetypes emerge, differentiated by bulk sulfur content: a CO$_2$-dominated and an SO$_2$-dominated atmosphere. Migration is viable but not required to reproduce the observations. Our study illustrates how interior--atmosphere coupling governs atmospheric retention on irradiated rocky planets.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.03144",
  "author_total": 13,
  "authors": [
    {
      "name": "Emma Postolec"
    },
    {
      "name": "Tim Lichtenberg"
    },
    {
      "name": "Johanna K. Teske"
    },
    {
      "name": "Harrison Nicholls"
    },
    {
      "name": "Mara Attia"
    },
    {
      "name": "Anjali Piette"
    },
    {
      "name": "Lisa Dang"
    },
    {
      "name": "Nicole L. Wallack"
    },
    {
      "name": "Mykhaylo Plotnykov"
    },
    {
      "name": "Alex McGinty"
    },
    {
      "name": "Samuel Boucher"
    },
    {
      "name": "Bo Peng"
    },
    {
      "name": "Diana Valencia"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/69j5sdv638mnw.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.03144",
  "fulltext_url": null,
  "id": "69j5sdv638mnw",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.03144",
  "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"
    ],
    [
      "arxiv",
      "physics.ao-ph"
    ],
    [
      "openalex",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7208755667",
  "pdf_url": "https://arxiv.org/pdf/2609.03144",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-02",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/69j5sdv638mnw.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:31Z",
      "native_id": "2609.03144",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.03144"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    },
    {
      "field": "earth",
      "origin": "arxiv:physics.ao-ph",
      "subfield": "atmospheric"
    }
  ],
  "title": "Evolutionary pathways toward survival of a thick CO2- or SO2-rich atmosphere on the lava world TOI-561 b",
  "title_text": "Evolutionary pathways toward survival of a thick CO2- or SO2-rich atmosphere on the lava world TOI-561 b",
  "type": "preprint",
  "updated_at": "2026-10-30T12:18:31Z",
  "url": "https://research.draconitic.com/paper/69j5sdv638mnw",
  "venue": "arXiv",
  "versions": []
}