{
  "abstract": "Recent exoplanet demographics studies have uncovered the Neptune ridge: an overdensity of intermediate-size planets at orbital periods between 3--6~d. The origin of this pile-up remains unclear, but it could be a consequence of high-eccentricity migration (HEM). Here, we confirm TOI-4129\\,b, a planet that may help to reveal the origin of the Neptune ridge. Using radial velocities from HARPS-N and transit photometry from TESS and four ground-based telescopes, we found that TOI-4129\\,b has a relatively low density ($R_p = 5.7 \\pm 0.2\\, R_\\oplus$, $M_p = 26\\pm 6 \\,M_\\oplus$, $ρ_p = 0.8 \\pm 0.2 ~\\textrm{g}~\\textrm{cm}^{-3}$) and orbits a $V = 12.9$ K dwarf star every 3.27~d, placing it at the inner edge of the Neptune ridge. We detect the stellar rotation period at 12.7~d in the photometry, implying a fairly young gyrochronal age of $1.20^{+0.16}_{-0.30}~$Gyr for the system. With a Transmission Spectroscopy Metric of $112\\pm 30$, this adolescent Neptune is a good target for atmospheric observations with \\textit{JWST} and \\textit{Ariel}, and we also find that it is amenable to future constraints on the (three-dimensional) stellar obliquity. TOI-4129\\,b will therefore be an important testing ground for the idea that planets in the Neptune ridge underwent HEM to arrive at their current locations.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2611.03810",
  "author_total": 39,
  "authors": [
    {
      "name": "Sureena Lakhanpal"
    },
    {
      "name": "Shreyas Vissapragada"
    },
    {
      "name": "Luca Naponiello"
    },
    {
      "name": "Simone Filomeno"
    },
    {
      "name": "Katia Biazzo"
    },
    {
      "name": "Vincent Bourrier"
    },
    {
      "name": "Tiziano Zingales"
    },
    {
      "name": "Erik Friden"
    },
    {
      "name": "Emily K. Pass"
    },
    {
      "name": "Aldo S. Bonomo"
    },
    {
      "name": "David W. Latham"
    },
    {
      "name": "Karen A. Collins"
    },
    {
      "name": "David R. Ciardi"
    },
    {
      "name": "David Baker"
    },
    {
      "name": "Khalid Barkaoui"
    },
    {
      "name": "Andrew Collier Cameron"
    },
    {
      "name": "Patrick Eggenberger"
    },
    {
      "name": "Akihiko Fukui"
    },
    {
      "name": "Ancy Anna John"
    },
    {
      "name": "Heather A. Knutson"
    },
    {
      "name": "Mercedes López-Morales"
    },
    {
      "name": "Jack Lubin"
    },
    {
      "name": "Luigi Mancini"
    },
    {
      "name": "Francesca Manni"
    },
    {
      "name": "Giacomo Mantovan"
    },
    {
      "name": "Annelies Mortier"
    },
    {
      "name": "Felipe Murgas"
    },
    {
      "name": "Norio Narita"
    },
    {
      "name": "Belinda A. Nicholson"
    },
    {
      "name": "Enric Palle"
    },
    {
      "name": "Matteo Pinamonti"
    },
    {
      "name": "Monica Rainer"
    },
    {
      "name": "Carolina Rodriguez"
    },
    {
      "name": "Pam Rowden"
    },
    {
      "name": "Miquel Serra-Ricart"
    },
    {
      "name": "Alessandro Sozzetti"
    },
    {
      "name": "Ivan A. Strakhov"
    },
    {
      "name": "Jhon Yana Galarza"
    },
    {
      "name": "Samuel W. Yee"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/47cgxe91e89ra.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.03810",
  "fulltext_url": null,
  "id": "47cgxe91e89ra",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.03810",
  "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": null,
  "pdf_url": "https://arxiv.org/pdf/2611.03810",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-02",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/47cgxe91e89ra.ris",
  "sources": [
    {
      "first_seen": "2026-11-04T15:21:25Z",
      "native_id": "2611.03810",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.03810"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "The Hot Neptune Initiative (HONEI): IV. TOI-4129 b, an Adolescent Neptune in the Ridge",
  "title_text": "The Hot Neptune Initiative (HONEI): IV. TOI-4129 b, an Adolescent Neptune in the Ridge",
  "type": "preprint",
  "updated_at": "2026-11-05T15:20:35Z",
  "url": "https://research.draconitic.com/paper/47cgxe91e89ra",
  "venue": "arXiv",
  "versions": []
}