{"paper":{"title":"Three-dimensional transport-induced chemistry on temperate sub-Neptune K2-18b, Part II: the combined effects of atmospheric dynamics and chemical reactions","license":"http://creativecommons.org/licenses/by/4.0/","headline":"Vertical transport on K2-18b lifts CO and CO2 abundances in the upper atmosphere to ~10^{-3} while equilibrium chemistry predicts levels below 10^{-15}.","cross_cats":[],"primary_cat":"astro-ph.EP","authors_text":"Duncan Christie, Jiachen Liu, Jun Yang, Krisztian Kohary","submitted_at":"2026-04-09T08:55:46Z","abstract_excerpt":"The upper atmospheres of temperate sub-Neptunes are strongly influenced by atmospheric dynamics due to their cool equilibrium temperature and thereby longer chemical timescales than the atmospheric dynamical timescales. In this study, we used a three-dimensional (3D) general circulation model to investigate the transport-induced disequilibrium chemistry and vertical mixing on temperate gas-rich mini-Neptunes, using K2-18b as an example. We model K2-18b assuming 180 times solar metallicity and consider it as either a synchronous or an asynchronous rotator, exploring spin-orbit resonances of 2:1"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"Vertical transport affects the chemical structure significantly, making CO2 and CO more abundant (~10^{-3}) in the upper atmosphere compared to the chemical equilibrium abundance (<10^{-15}), and horizontal winds further homogenize the chemical composition zonally in this region.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"That the chosen 180x solar metallicity, the specific chemical network, and the GCM resolution together produce realistic chemical timescales and transport without missing key processes such as clouds or photochemistry.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"3D GCM modeling of K2-18b finds that transport-induced disequilibrium raises upper-atmosphere CO and CO2 to ~10^{-3} while horizontal winds homogenize composition, yielding spectra that match JWST observations.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"Vertical transport on K2-18b lifts CO and CO2 abundances in the upper atmosphere to ~10^{-3} while equilibrium chemistry predicts levels below 10^{-15}.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"66e4931bebe27cc101eb86e84b6293e0158272e668b64cc6d88ed77cbf933b57"},"source":{"id":"2604.07987","kind":"arxiv","version":2},"verdict":{"id":"7074b054-ee15-4087-8407-0b78e69ae9f0","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-10T17:21:35.433536Z","strongest_claim":"Vertical transport affects the chemical structure significantly, making CO2 and CO more abundant (~10^{-3}) in the upper atmosphere compared to the chemical equilibrium abundance (<10^{-15}), and horizontal winds further homogenize the chemical composition zonally in this region.","one_line_summary":"3D GCM modeling of K2-18b finds that transport-induced disequilibrium raises upper-atmosphere CO and CO2 to ~10^{-3} while horizontal winds homogenize composition, yielding spectra that match JWST observations.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"That the chosen 180x solar metallicity, the specific chemical network, and the GCM resolution together produce realistic chemical timescales and transport without missing key processes such as clouds or photochemistry.","pith_extraction_headline":"Vertical transport on K2-18b lifts CO and CO2 abundances in the upper atmosphere to ~10^{-3} while equilibrium chemistry predicts levels below 10^{-15}."},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2604.07987/integrity.json","findings":[],"available":true,"detectors_run":[],"snapshot_sha256":"c28c3603d3b5d939e8dc4c7e95fa8dfce3d595e45f758748cecf8e644a296938"},"references":{"count":3,"sample":[{"doi":"10.5281/zenodo.8305232","year":2016,"title":"S., et al., 2016, A&A, 595, A36 BaeyensR.,KoningsT.,VenotO.,CaroneL.,DecinL.,2022,MNRAS,512, 4877 Barrier E","work_id":"bcc29e3b-5259-42b0-be75-937eb9ee33e9","ref_index":1,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"10.1007/978-94-010-1799-2_4","year":2021,"title":"ed RS Stepleman et al Hu R., Damiano M., 2021, Deep Characterization of the Atmosphere of a Temperate Sub-Neptune, JWST Proposal. Cycle 1, ID. #2372 Hu R., Damiano M., Scheucher M., Kite E., Seager S.","work_id":"076ad850-1983-48da-88ad-f3a2888fe999","ref_index":2,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":2026,"title":"Results are derived from simulated data over the first 100 d, in which the horizontal temperature contrast begins to form, with an output interval of 10 d","work_id":"f659de86-1771-47d5-a496-d2e821a83f90","ref_index":3,"cited_arxiv_id":"","is_internal_anchor":false}],"resolved_work":3,"snapshot_sha256":"3178d53e5659a1634a803d7ea27b13f3b031750fefdf3a5f96c84ed16dd44062","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}