{"paper":{"title":"POSEIDON I: The Dynamical Origins of Transiting Neptunes","license":"http://creativecommons.org/licenses/by/4.0/","headline":"","cross_cats":[],"primary_cat":"astro-ph.EP","authors_text":"Andr\\'es Jord\\'an, Cristobal Petrovich, Elise Koo, Felipe I. Rojas, Gavin Boyle, Gu{\\dh}mundur Stef\\'ansson, Hareesh Bhaskar, Hugo Veldhuis, Jeffrey D. Crane, Johanna K. Teske, Joshua N. Winn, Juan I. Espinoza-Retamal, Marcelo Tala Pinto, Melissa J. Hobson, Rafael Brahm, Rodrigo Leiva, R. Paul Butler, Shreyas Vissapragada, Stephen Shectman, Vincent Suc","submitted_at":"2026-02-20T19:00:00Z","abstract_excerpt":"We present the first results from the POSEIDON survey, aimed at constraining the dynamical origins of transiting Neptunes through stellar obliquity measurements. We report Rossiter-McLaughlin observations of two Neptunes, TOI-181 b and TOI-883 b, obtained with high-resolution spectroscopy from Magellan/PFS and WIYN/NEID. TOI-181 b is on a 4.5-day orbit with a sky-projected spin-orbit misalignment $\\lambda = 32.0_{-6.5}^{+6.3}\\,^{\\circ}$ and a low eccentricity ($e<0.12$ with $2\\sigma$ confidence). TOI-883 b has a longer orbital period of 10 days with $\\lambda = 22_{-14}^{+15}\\,^{\\circ}$ and ecc"},"claims":{"count":0,"items":[],"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"source":{"id":"2602.18553","kind":"arxiv","version":2},"verdict":{"id":null,"model_set":{},"created_at":null,"strongest_claim":"","one_line_summary":"","pipeline_version":null,"weakest_assumption":"","pith_extraction_headline":""},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2602.18553/integrity.json","findings":[],"available":true,"detectors_run":[],"snapshot_sha256":"c28c3603d3b5d939e8dc4c7e95fa8dfce3d595e45f758748cecf8e644a296938"},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}