{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/tidal-inflation-reconciles-low-density-sub","title":"Tidal Inflation Reconciles Low-Density Sub-Saturns with Core Accretion","arxiv_id":"2005.11209","date":"2020-05-22","proceeding":null,"authors":["Sarah Millholland","Erik Petigura","Konstantin Batygin"],"abstract":"While the Solar System contains no planets between the sizes of Uranus and Saturn, our current exoplanet census includes several dozen such planets with well-measured masses and radii. These sub-Saturns exhibit a diversity of bulk densities, ranging from ~$0.1-3\\ \\rm{g\\ cm}^{-3}$. When modeled simply as hydrogen/helium envelopes atop rocky cores, this diversity in densities translates to a diversity in planetary envelope fractions, $f_\\rm{env}=M_\\rm{env}/M_p$ ranging from ~$10\\%$ to ~$50\\%$. Planets with $f_\\rm{env}\\sim50\\%$ pose a challenge to traditional models of giant planet formation by core-nucleated accretion, which predict the onset of runaway gas accretion when $M_\\rm{env}\\sim M_\\rm{core}$. Here we show that many of these apparent $f_\\rm{env}\\sim50\\%$ planets are less envelope rich than they seem, after accounting for tidal heating. We present a new framework for modeling sub-Saturn interiors that incorporates envelope inflation due to tides, which are driven by the observed non-zero eccentricities, as well as potential obliquities. Consequently, when we apply our models to known sub-Saturns, we infer lower $f_\\rm{env}$ than tides-free estimates. We present a case study of K2-19 b, a moderately eccentric sub-Saturn. Neglecting tides, K2-19 b appears to have $f_\\rm{env}\\sim50\\%$, poised precariously near the runaway threshold; by including tides, we find $f_\\rm{env}\\sim10\\%$, resolving the tension. Through a systematic analysis of $4-8\\ R_{\\oplus}$ planets, we find that most (but not all) of the similarly envelope-rich planets have more modest envelopes of $f_\\rm{env}\\sim10\\%-20\\%$. Thus, many sub-Saturns may be understood as sub-Neptunes that have undergone significant radius inflation, rather than a separate class of objects. Tidal radius inflation likely plays an important role in other size classes of planets including ultra-low-density Jupiter-size planets like WASP-107 b.","url_abs":"http://arxiv.org/abs/2005.11209v1","url_pdf":"http://arxiv.org/pdf/2005.11209v1.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"tidal-inflation-reconciles-low-density-sub","repo_url":"https://github.com/smillholland/Sub-Saturns","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":null,"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}