{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"2e4806264da44f2dc596cc21bd667b37b903631280d6d6de2ddb9e9afc422dd2","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["acec1fa3e365c28f216f060c6e80c64d72eb3d1ee9eb25bf00f82874e1a2d4b1","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"6cdcb2795fadd51373a6ae45ad4bcff39781b7ecc9759877afa678a3cc31727a","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"astro.biosignatures.eta-earth","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"The fraction of Sun-like stars with an Earth-size planet at a distance where water could be liquid sets how many targets future telescopes can study. Current estimates differ by about a factor of ten.","posed_since":"","precise":"Measure $\\eta_{\\mathrm{Earth}}$, the number per G and K dwarf of planets with $R = 0.5-1.5\\,R_{\\mathrm{earth}}$ in the conservative habitable zone. Kepler-based estimates span roughly 0.05-0.6 because of extrapolation in period and radius and stellar property uncertainties. The answer is a value with uncertainty below $\\sim 30\\%$.","problem_ref":"acec1fa3e365c28f216f060c6e80c64d72eb3d1ee9eb25bf00f82874e1a2d4b1","references":"","settled_by":"A transit survey of bright Sun-like stars with sensitivity to Earth analogs over multi-year baselines (e.g., ESA PLATO), with radial-velocity mass follow-up.","status_note":"","title":"How common are Earth-size planets in habitable zones of Sun-like 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