{
  "abstract": "The James Webb Space Telescope (JWST) has enabled the first in-depth characterisations of sub-Neptune atmospheres, revealing a diversity of chemical compositions and cloud properties that challenge current models. Multi-planet systems provide an opportunity to compare planetary atmospheres while controlling for formation conditions within the same protoplanetary disk. We present JWST NIRSpec G395H 3-5 um observations of two similarly-sized sub-Neptunes orbiting a sun-like star within the TOI-125 system: TOI-125 b ($P=4.65$ d, $R_p=2.7~R_\\oplus$, $M_p=10~M_\\oplus$, $T_\\mathrm{eq}=1100$ K) and TOI-125 c ($P=9.15$ d, $R_p=2.85~R_\\oplus$, $M_p=6.8~M_\\oplus$, $T_\\mathrm{eq}=825$ K), comprising of one full transit of TOI-125 b but only 70% of TOI-125 c's transit due to larger than predicted TTVs. We obtain precise R~100 transmission spectra for both planets, with median errorbars of 50 ppm for TOI-125 b and 85 ppm for TOI-125 c. Atmospheric retrievals are compatible with a ~150x solar metallicity atmosphere or clouds above ~3 mbar for TOI-125 b, and a ~100x solar metallicity atmosphere or clouds above ~10 mbar for TOI-125 c. Our results may support recent evidence for metal enrichment in sub-Neptunes, while also further complicating the proposed trend in atmospheric feature size with planet temperature. However, shorter wavelength follow-up observations of both planets are needed to establish whether their spectra are truly muted or feature-rich, with implications for the nature of sub-Neptunes around sun-like stars.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.35607",
  "author_total": 13,
  "authors": [
    {
      "name": "Yiwei Chai"
    },
    {
      "name": "Néstor Espinoza"
    },
    {
      "name": "Chloe Fisher"
    },
    {
      "name": "Erik Meier Valdes"
    },
    {
      "name": "Matthew Hooton"
    },
    {
      "name": "Brett Morris"
    },
    {
      "name": "Natalie H. Allen"
    },
    {
      "name": "Adam J. Burgasser"
    },
    {
      "name": "Brice-Olivier Demory"
    },
    {
      "name": "Amélie Gressier"
    },
    {
      "name": "Kevin Heng"
    },
    {
      "name": "Mercedes López-Morales"
    },
    {
      "name": "Meng Tian"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/epbb22fk6vq0w.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.35607",
  "fulltext_url": null,
  "id": "epbb22fk6vq0w",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.35607",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.EP"
    ],
    [
      "openalex",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7214714913",
  "pdf_url": "https://arxiv.org/pdf/2609.35607",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-28",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/epbb22fk6vq0w.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:25:12Z",
      "native_id": "2609.35607",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.35607"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "JWST NIRSpec G395H Transmission Spectra of Two Similar Sub-Neptunes in the TOI-125 System",
  "title_text": "JWST NIRSpec G395H Transmission Spectra of Two Similar Sub-Neptunes in the TOI-125 System",
  "type": "preprint",
  "updated_at": "2026-10-30T12:25:12Z",
  "url": "https://research.draconitic.com/paper/epbb22fk6vq0w",
  "venue": "arXiv",
  "versions": []
}