Baliwal, SanjaySanjayBaliwalSharma, RishikeshRishikeshSharmaChakraborty, AbhijitAbhijitChakrabortyKhandelwal, AkankshaAkankshaKhandelwalNikitha, K. J.K. J.NikithaSafonov, Boris S.Boris S.SafonovStrakhov, Ivan A.Ivan A.StrakhovMontalto, MarcoMarcoMontaltoEastman, Jason D.Jason D.EastmanLatham, David W.David W.LathamBieryla, AllysonAllysonBierylaPrasad, Neelam J.S.S.V.Neelam J.S.S.V.PrasadBharadwaj, Kapil K.Kapil K.BharadwajLad, Kevikumar A.Kevikumar A.LadDas, Shubhendra N.Shubhendra N.DasNayak, AshirbadAshirbadNayak2025-08-312025-08-312024-11-0110.1051/0004-6361/2024509342-s2.0-85208221333https://d8.irins.org/handle/IITG2025/28683We report the discovery and characterization of a transiting sub-Saturn exoplanet TOI-6651b using PARAS-2 spectroscopic observations. The host, TOI-6651 (m<inf>V</inf> ≈ 10.2), is a sub-giant, metal-rich G-type star with [Fe / H] = 0.225<inf>-0.045</inf>^0.044[Fe/H] = 0.225<inf>-0.045</inf>^+0.044, T<inf>eff</inf> = 5940 ± 110 K, and log g = 4.087<inf>-0.032</inf>^+0.035. Joint fitting of the radial velocities from PARAS-2 spectrograph and transit photometric data from Transiting Exoplanet Survey Satellite (TESS) reveals a planetary mass of 61.0<inf>-7.9</inf>^+7.6 M<inf>⊕</inf> and radius of 5.09<inf>-0.26</inf>^+0.27 R<inf>⊕</inf>, in a 5.056973<inf>-0.000018</inf>^+0.000016 day orbit with an eccentricity of 0.091<inf>-0.062</inf>^+0.096. TOI-6651b has a bulk density of 2.52<inf>-0.44</inf>^+0.52 g cm^-3, positioning it among the select few known dense sub-Saturns and making it notably the densest detected with TESS. TOI-6651b is consistent with the positive correlation between planet mass and the host star's metallicity. We find that a considerable portion ≈ 87% of the planet's mass consists of dense materials such as rock and iron in the core, while the remaining mass comprises a low-density envelope of H/He. TOI-6651b lies at the edge of the Neptunian desert, which will be crucial for understanding the factors shaping the desert boundaries. The existence of TOI-6651b challenges conventional planet formation theories and could be a result of merging events or significant atmospheric mass loss through tidal heating, highlighting the complex interplay of dynamical processes and atmospheric evolution in the formation of massive dense sub-Saturns.trueMethods: observational | Planets and satellites: detection | Stars: individual: TOI-6651 | Techniques: photometric | Techniques: radial velocitiesArticlehttps://doi.org/10.1051/0004-6361/202450934143207461 November 20242A12arJournal2