{
  "abstract": "Sub-Neptunes are the most common short-period ($P<100$ d) planets known. A major goal for the field is to build a comprehensive understanding of their compositions and evolutionary histories, and an important tool for achieving this goal is metastable helium (He$^*$) transmission spectroscopy, which traces atmospheric escape. In this paper, we report the detection of He$^*$ in the atmosphere of the sub-Neptune GJ 3090b at high spectral resolution. We observed two consecutive transits of this planet with Magellan II/WINERED, and detected peak He$^*$ absorptions during transit of $2.033\\pm0.086\\%$ (23.6$σ$) and $1.619\\pm0.122\\%$ (13.3$σ$), respectively. The first transit was affected by a stellar flare near egress while the second transit was unaffected. The signal is variable in amplitude and deeper than anticipated by the JWST/NIRISS observations of Ahrer et al. (2025). We do not observe a significant Doppler shift, and the signal has a FWHM of $25$ km s$^{-1}$, implicating photoevaporation. Our outflow modeling suggests that $Z_\\mathrm{atm}\\lesssim100\\times$ solar, as the observed He$^*$ amplitudes are challenging to achieve in a metal-rich atmosphere. To match the muted transmission spectra from JWST and VLT/CRIRES+, GJ 3090b's lower atmosphere is likely covered by aerosols. Finally, we found that GJ 3090b has an atmospheric lifetime of $\\sim300$ Myr, much shorter than previously reported. This adolescent ($\\sim1$ Gyr) sub-Neptune is currently in a transformative phase of photoevaporative evolution.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.14704",
  "author_total": 15,
  "authors": [
    {
      "name": "Shreyas Vissapragada"
    },
    {
      "name": "Zifan Lin"
    },
    {
      "name": "Annabella Meech"
    },
    {
      "name": "Collin Cherubim"
    },
    {
      "name": "Leonardo A. Dos Santos"
    },
    {
      "name": "Aaron Householder"
    },
    {
      "name": "Krishna Kanumalla"
    },
    {
      "name": "Mercedes Lopez-Morales"
    },
    {
      "name": "Andrew McWilliam"
    },
    {
      "name": "William Misener"
    },
    {
      "name": "Ava Morrissey"
    },
    {
      "name": "Morgan Saidel"
    },
    {
      "name": "Jessica J. Spake"
    },
    {
      "name": "Johanna Teske"
    },
    {
      "name": "Nicole L. Wallack"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7wcfdhj6eebkq.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.14704",
  "fulltext_url": null,
  "id": "7wcfdhj6eebkq",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.14704",
  "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",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7213317138",
  "pdf_url": "https://arxiv.org/pdf/2609.14704",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-13",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/7wcfdhj6eebkq.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:21:25Z",
      "native_id": "2609.14704",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.14704"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "WINERED Detects a Strong Atmospheric Outflow on the Sub-Neptune GJ 3090b",
  "title_text": "WINERED Detects a Strong Atmospheric Outflow on the Sub-Neptune GJ 3090b",
  "type": "preprint",
  "updated_at": "2026-10-30T12:21:25Z",
  "url": "https://research.draconitic.com/paper/7wcfdhj6eebkq",
  "venue": "arXiv",
  "versions": []
}