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    "story_id": "mp-2026-09-10-027",
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    "headline": "Small Planets Changed Composition With Their Host Stars",
    "slug": "small-planets-changed-composition-with-their-host-stars",
    "dek": "Population models inferred rockier planets around Sun-like stars and tightly bounded volatile inventories around M dwarfs.",
    "summary": "Population models inferred rockier planets around Sun-like stars and tightly bounded volatile inventories around M dwarfs.",
    "body_text": "A mixture model linked interior structures to the measured density distributions of small planets in three samples. Under one rocky-population parameterization, planets around FGK stars had characteristic core mass fractions about 16 percent higher than planets around M dwarfs. An alternative model estimated 89.9 to 97.0 percent of FGK-hosted planets as rocky, while the M-dwarf rocky share remained much less certain. Volatile-bearing planets were common in the model but concentrated at small atmospheric and water fractions. These are population-level inferences shaped by sample selection and interior-model assumptions, not direct compositional measurements of individual worlds.",
    "why_it_matters": "Population models inferred rockier planets around Sun-like stars and tightly bounded volatile inventories around M dwarfs.",
    "limitations": [
      "These are population-level inferences shaped by sample selection and interior-model assumptions, not direct compositional measurements of individual worlds."
    ],
    "importance": 8,
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    "first_published_at": "2026-09-10T09:00:00.000-04:00",
    "modified_at": "2026-09-10T09:00:00.000-04:00",
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        "text": "Population models inferred rockier planets around Sun-like stars and tightly bounded volatile inventories around M dwarfs.",
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          "source-2026-09-10-016"
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        "qualification": "These are population-level inferences shaped by sample selection and interior-model assumptions, not direct compositional measurements of individual worlds."
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      "source-2026-09-10-016"
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    "tags": [
      "exoplanets",
      "planet composition",
      "stellar type"
    ],
    "image_url": null,
    "corrections": []
  },
  "sources": [
    {
      "source_id": "source-2026-09-10-016",
      "title": "arXiv preprint 2609.09319",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2609.09319",
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      "source_type": "primary_research",
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      "published_at": "2026-09-07T20:00:00.000-04:00",
      "accessed_at": "2026-09-10T08:24:00.000-04:00",
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    "name": "The Machine Press",
    "url": "https://themachinepress.com",
    "description": "A daily newspaper for the age of artificial intelligence."
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  "cite_this_report": {
    "title": "Small Planets Changed Composition With Their Host Stars",
    "publisher": "The Machine Press",
    "published_at": "2026-09-10T09:00:00.000-04:00",
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