{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"8f3fe461150286aca64166f8b5c7e2d1901b59d026088f68e391c90d432c88a4","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["01c5f5dd665eae067eb5d6c8253423757d9d7fa5a4a0d2316a19ea2138c682b3","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"41760d1eaee8074e89a70415be2186a5fdeef8cb9dbd084b6c410818a979a6bd","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"astro.radius-valley.water-worlds","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Planets that formed beyond the line where water freezes and then moved inward could be up to half water by mass. Whether any such water worlds exist among close-in sub-Neptunes has not been shown.","posed_since":"","precise":"Determine whether any planet with $R \\sim 1.5-3.5\\ R_{\\mathrm{earth}}$ and $P < 100\\ \\mathrm{d}$ has a water mass fraction above 0.1, demonstrated by a combination of bulk density and an atmospheric mean molecular weight and $\\mathrm{H_2O}$ abundance that a rocky core with an H/He envelope or a magma-ocean model cannot reproduce. The answer is yes or no, with the planets and water fractions if yes.","problem_ref":"01c5f5dd665eae067eb5d6c8253423757d9d7fa5a4a0d2316a19ea2138c682b3","references":"","settled_by":"JWST spectra giving high mean molecular weight and $\\mathrm{H_2O}$-dominated composition for a planet whose mass and radius are measured to better than 10 and 3 percent, fitted with interior models that include supercritical water and hydrogen-water mixing.","status_note":"A 2025 JWST analysis interpreted K2-18 b as water-rich (arXiv:2507.12622), but gas-rich mini-Neptune and magma-ocean models also fit its spectrum.","title":"Do sub-Neptunes with more than 10 percent water 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