Dynamical and Atmospheric Evolution of TOI-5734 b: a Hot Sub-Neptune at The Edge of The Radius Valley

Abstract

Bijay Kumar Sharma

We present a dynamical and structural investigation of the recently discovered hot sub-Neptune TOI-5734 b, a short-period exoplanet located near the upper boundary of the radius valley. Identified through photometric observations by the Transiting Exoplanet Survey Satellite and radial-velocity measurements from the HARPS-N spectrograph at the Galileo National Telescope, the planet orbits a young K-dwarf star at a separation of approximately 0.06 AU with an orbital period of 6.18 days. With a radius of 2.1 �??⊕ and mass of 9.1 �??⊕, TOI 5734 b lies in the transitional regime between super-Earths and gas-rich sub-Neptunes. Its bulk density indicates a predominantly rocky interior with a residual volatile envelope. The intense stellar irradiation corresponding to an equilibrium temperature of 688 K strongly favors ongoing atmospheric escape. Evolutionary considerations suggest that the planet may lose most of its primordial atmosphere within 3×108 years. We analyze the orbital and angular-momentum evolution of the system using a primary-centric dynamical framework, examining tidal dissipation, migration history, and long- term orbital stability. The planet’s present position near the radius gap supports atmospheric erosion driven by photoevaporation and/or core-powered mass loss. TOI-5734 b thus provides an important laboratory for understanding the physical mechanisms that sculpt the dominant intermediate-mass planet population and offers key insights into the evolutionary pathways linking sub-Neptunes and super-Earths.

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