{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"099f09417c028376dc173c967e306e46f80a8924cc310ebac53f22e60dfa7c5c","created":"2026-10-03T07:17:55Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"2a0314458c0374ab74daf3fdf8435cd78ed76683e6f3a2fa5459a6f7b558b8e3","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"classification","assisted_by":[],"external_id":"astro.radius-valley.sub-neptune-composition","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"A planet two or three times Earth's size can be a rocky ball with a thin hydrogen layer or a world with a large fraction of water, and mass and radius alone cannot tell which. Their atmospheres carry clues.","posed_since":"","precise":"For planets with $R \\sim 2-3.5\\,R_{\\mathrm{earth}}$ and $M \\sim 5-15\\,M_{\\mathrm{earth}}$, determine the bulk composition: rocky cores with H/He envelopes of $\\sim 1-3\\text{ percent}$ by mass, water mass fractions of $\\sim 10-50\\text{ percent}$ in supercritical layers, or magma oceans that dissolve and mix with hydrogen. The answer is a classification of individual planets and the population fractions, using JWST transmission spectra (mean molecular weight, H2O, CH4, CO2, NH3 abundances) together with interior models.","problem_ref":null,"references":"","settled_by":"High signal-to-noise transmission and emission spectra of a sample of temperate and warm sub-Neptunes fitted with coupled interior-atmosphere models.","status_note":"","title":"Are sub-Neptunes rocky cores with hydrogen or water worlds?","topic_ref":"29eecacca9d688759063e837d47b7481ed1a91ff74dcb512159e65510cf6039a"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"c1da01cccdab995103bb69427c0d76cbe17fda1b6a2e1c2046fa8d24c99ef764","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"854fc96c46edaca7d98491b09492accb116d6b827fcf1c5c9bcae02538bd85af","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"7MJSlmTUwpMaXPsafarLcrixCqsYAcBIkVuo1K2VJN_xxzuMcNTIxbM6PwwdjOL0OfpHYcxb5suyz4Hay73xDw"},"schema":"pubphys.envelope/1"},"record_hash":"c1da01cccdab995103bb69427c0d76cbe17fda1b6a2e1c2046fa8d24c99ef764","leaf_index":599}