{ "abstract": "We present a Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G141 phase-curve observation of the ultrashort-period rocky planet TOI-2431 b and detect its secondary eclipse in the near-infrared. Combined with the TESS optical eclipse, these measurements constrain the planet’s dayside brightness temperature, reflected light contribution, albedo, and heat redistribution. We detect the eclipse in the optical and near-infrared wavelengths of TESS and HST/WFC3 G141, with a planet-to-star flux ratio of 37 ± 10 ppm and 6 9 − 13 + 14 ppm , respectively. Assuming negligible reflected light, the joint TESS+HST fit yields a brightness temperature T b , joint = 252 4 − 84 + 77 K and a brightness temperature ratio of R joint = T b , joint / T p , max = 0.98 0 − 0.034 + 0.032 consistent with the zero-albedo, no-redistribution limit T p , max = 257 4 − 35 + 36 K . The HST phase curve is consistent with zero nightside emission and no measurable hotspot offset, consistent with inefficient day-night heat distribution. Under this thermal-dominated interpretation, TOI-2431 b lies at the zero-albedo, no-redistribution limit and contrasts with previously observed lava worlds. At optical and near-infrared wavelengths, however, thermal emission is degenerate with reflected light. For a geometric albedo of A g = 0.1, reflected light would contribute approximately 11 ppm in each bandpass, reducing the temperature to T b , joint ( A g = 0.1 ) = 240 7 − 102 + 91 K . Longer-wavelength observations are required to isolate the thermal component. Planned JWST/MIRI LRS observations are expected to substantially reduce this degeneracy and provide more direct constraints on heat redistribution and possible silicate-atmosphere spectral features. This marks the first secondary eclipse detection of a rocky exoplanet using HST and establishes TOI-2431 b as a benchmark target for studying properties of lava worlds.", "abstract_shown": true, "affiliations": [ "Center for Astrophysics", "SRON", "Leiden Observatory", "McGill University", "Max Planck Institute for Astronomy", "Space Telescope Science Institute", "University of Waterloo", "Università di Padova", "INAF—Osservatorio Astronomico di Padova", "Leiden University", "University of Warwick", "California Institute of Technology", "Université de Montréal", "University of Kansas", "University of Vienna", "University of Texas at Austin", "University of Groningen", "University of Bern" ], "article_type": null, "arxiv": null, "author_total": 21, "authors": [ { "affs": [ 0 ], "name": "Sebastian Zieba", "orcid": "0000-0003-0562-6750" }, { "affs": [ 1 ], "name": "Billy Edwards", "orcid": "0000-0002-5494-3237" }, { "affs": [ 0 ], "name": "Samuel N. Quinn", "orcid": "0000-0002-8964-8377" }, { "affs": [ 2 ], "name": "Leoni Janssen", "orcid": "0009-0002-9902-731X" }, { "affs": [ 3 ], "name": "Nicolas B. Cowan", "orcid": "0000-0001-6129-5699" }, { "affs": [ 4 ], "name": "Laura Kreidberg", "orcid": "0000-0003-0514-1147" }, { "affs": [ 5 ], "name": "Mercedes López-Morales", "orcid": "0000-0003-3204-8183" }, { "affs": [ 6 ], "name": "Lisa Dang", "orcid": "0000-0003-4987-6591" }, { "affs": [ 7, 8 ], "name": "Luca Malavolta", "orcid": "0000-0002-6492-2085" }, { "affs": [ 1, 9 ], "name": "Yamila Miguel", "orcid": "0000-0002-0747-8862" }, { "affs": [ 3 ], "name": "T. Giang Nguyen", "orcid": "0000-0001-6171-200X" }, { "affs": [ 0 ], "name": "Andrew Vanderburg", "orcid": "0000-0001-7246-5438" }, { "affs": [ 10 ], "name": "Thomas G. Wilson", "orcid": "0000-0001-8749-1962" }, { "affs": [ 11 ], "name": "Mantas Zilinskas", "orcid": "0000-0002-8749-823X" }, { "affs": [ 6, 12 ], "name": "Nicholas J. Connors", "orcid": "0000-0001-5848-6750" }, { "affs": [ 13 ], "name": "Ian J. M. Crossfield" }, { "affs": [ 14 ], "name": "Oliver Herbort", "orcid": "0000-0002-1807-4441" }, { "affs": [ 15 ], "name": "Adam L. Kraus", "orcid": "0000-0001-9811-568X" }, { "affs": [ 16 ], "name": "Tim Lichtenberg", "orcid": "0000-0002-3286-7683" }, { "affs": [ 16 ], "name": "Mariana Sastre", "orcid": "0009-0008-7799-7976" }, { "affs": [ 17 ], "name": "Joost P. Wardenier", "orcid": "0000-0003-3191-2486" } ], "bibtex": "https://research.draconitic.com/paper/3ftp64b8e0fbw.bib", "cited_by": 0, "doi": "10.3847/2041-8213/aeb4ab", "fulltext_url": null, "id": "3ftp64b8e0fbw", "issns": [ "2041-8213", "2041-8205" ], "landing_url": "https://iopscience.iop.org/article/10.3847/2041-8213/aeb4ab", "language": null, "licence": "CC-BY-4.0", "licence_label": "CC BY 4.0", "licence_source": "article", "licence_url": "https://creativecommons.org/licenses/by/4.0/", "metadata_licence": null, "native_subjects": [ [ "feed-journal", "astronomy/general" ] ], "openalex": null, "pdf_url": "https://iopscience.iop.org/article/10.3847/2041-8213/aeb4ab/pdf", "pmcid": null, "pmid": null, "published": "2026-10-30", "publisher": "American Astronomical Society", "ris": "https://research.draconitic.com/paper/3ftp64b8e0fbw.ris", "sources": [ { "first_seen": "2026-10-30T18:20:22Z", "native_id": "10.3847/2041-8213/aeb4ab", "source": "feed-iop", "url": "https://iopscience.iop.org/article/10.3847/2041-8213/aeb4ab" }, { "first_seen": "2026-10-31T00:20:43Z", "native_id": "10.3847/2041-8213/aeb4ab", "source": "crossref", "url": "https://iopscience.iop.org/article/10.3847/2041-8213/aeb4ab" } ], "subjects": [ { "field": "astronomy", "origin": "journal-openalex:3103|Stellar, planetary, and galactic studies", "subfield": "stellar" } ], "title": "The First Hubble Detection of a Secondary Eclipse from a Rocky Exoplanet: The 5.4 hr Planet TOI-2431 b", "title_text": "The First Hubble Detection of a Secondary Eclipse from a Rocky Exoplanet: The 5.4 hr Planet TOI-2431 b", "type": "peer-reviewed", "updated_at": "2026-11-01T00:20:39Z", "url": "https://research.draconitic.com/paper/3ftp64b8e0fbw", "venue": "The Astrophysical Journal Letters", "versions": [] }