{
  "abstract": "Observations indicate that some hot Neptunes and Jupiters underwent high eccentricity migration (HEM). A longstanding issue facing HEM theory remains, however: in order to shrink their orbits by ${\\sim}1{-}2$ orders of magnitude, planets must dissipate ${\\gtrsim}10{\\times}$ more orbital energy than is contained in their structural binding energy. Previous work suggests that excitation of planets' fundamental modes (''$f$-modes'') at very high eccentricities, $e{\\sim}$0.99, can shrink semi-major axes by ${\\sim}$an order of magnitude (${\\sim}5{\\rightarrow}0.5$ au) while safely bleeding tidal energy to space. We examine how planets traverse the remaining order of magnitude in orbital shrinkage, $a{\\sim}$0.5${\\rightarrow}$0.05 au, which still poses a danger for Neptunian planets due to their lower binding energies (their ''final parsec'' problem). To assess whether tidally-migrating Neptunes balance their energy budgets, we perform coupled orbit/structure calculations tracking their frequency-dependent tidal response under inertial waves (IWs). We show that tidal radius inflation at moderate eccentricities sweeps Neptunes' fundamental modes back into resonance with tidal forcing; only a small amount of tidal heat relative to a Neptune's binding energy is needed to drive this $f$-mode excitation. This excitation of Neptunes' $f$-modes may offer a route to safe circularization, provided the $f$-mode dissipates without harming the planet. In contrast, eccentric gas giants ($e{\\sim}0.9$) circularize without drama over ${\\sim}$Gyr. Our theory predicts that warm Neptunes on a HEM track ($a{\\gtrsim}0.1 \\ \\mathrm{au}, \\ e{\\gtrsim}0.8$) should be rare, in opposition to warm gas giants and lower eccentricity Neptunes. Observational confirmation of our predictions would constrain the interior structures of Neptunian planets via tidal theory.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.12968",
  "author_total": 3,
  "authors": [
    {
      "name": "Tim Hallatt"
    },
    {
      "name": "Adrian J. Barker"
    },
    {
      "name": "Sarah C. Millholland"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/3ts01btxjjap6.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.12968",
  "fulltext_url": null,
  "id": "3ts01btxjjap6",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.12968",
  "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": "W7221559686",
  "pdf_url": "https://arxiv.org/pdf/2610.12968",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-09",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/3ts01btxjjap6.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:28:36Z",
      "native_id": "2610.12968",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.12968"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "The Neptunian Final Parsec Problem: How Inertial Waves Enable Neptunes and Gas Giants to Survive Tidal Migration",
  "title_text": "The Neptunian Final Parsec Problem: How Inertial Waves Enable Neptunes and Gas Giants to Survive Tidal Migration",
  "type": "preprint",
  "updated_at": "2026-10-30T12:28:36Z",
  "url": "https://research.draconitic.com/paper/3ts01btxjjap6",
  "venue": "arXiv",
  "versions": []
}