{
  "abstract": "Compact multi-planet systems orbiting ultracool dwarfs, such as TRAPPIST-1, may be a major population of terrestrial worlds with poorly constrained demographics. Individual close-in planets are expected to escape microlensing detection, but whether a compact system can produce a detectable collective signal remains to be quantified. We calculate the microlensing signal from each TRAPPIST-1 planet, and of all seven combined, if the system were a lens toward the bulge. For a 0.09 $M_\\odot$ lens at 4 kpc, $R_E \\approx 1.21$ AU, placing the planets at $s = 0.010$--$0.051~θ_E$, 12--63 times interior to the lensing zone. We measure each signal as the residual after fitting a single-lens model, which accounts for the barycentric dipole. Because the quadrupole term cancels between the two images to first order, the residual scales as the octupole ($q s^3$), reaching $|δA / A| \\sim 10^{-6}$. The seven planets combined yield $Δχ^2 \\sim 10^{-3}$ even at 1~mmag precision, five orders of magnitude below the standard detection threshold. Detection requires increasing all planet masses by a factor of $\\sim$300, whereas the resonant chain loses its guarantee of Hill stability at a factor of $\\sim$7. Only a lens within $\\sim$15 pc of the source or the Sun places the outer planets in the lensing zone. The Nancy Grace Roman Space Telescope is therefore not expected to detect a TRAPPIST-1-like system through microlensing, whereas its transit channel in the same fields can detect such planets in large numbers, marking a sharp boundary in the Galactic census between microlensing and transit sensitivity.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2611.05535",
  "author_total": 1,
  "authors": [
    {
      "name": "Stephen R. Kane"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/0fg0endtykgk9.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.05535",
  "fulltext_url": null,
  "id": "0fg0endtykgk9",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.05535",
  "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"
    ],
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "arxiv",
      "astro-ph.IM"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2611.05535",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/0fg0endtykgk9.ris",
  "sources": [
    {
      "first_seen": "2026-11-05T15:20:56Z",
      "native_id": "2611.05535",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.05535"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.IM",
      "subfield": "instrumentation-methods"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "On the Detectability of Compact Multi-Planet Systems via Gravitational Microlensing",
  "title_text": "On the Detectability of Compact Multi-Planet Systems via Gravitational Microlensing",
  "type": "preprint",
  "updated_at": "2026-11-07T18:20:05Z",
  "url": "https://research.draconitic.com/paper/0fg0endtykgk9",
  "venue": "arXiv",
  "versions": []
}