2025ApJ...986..224X

The observed exoplanet population exhibits a scarcity of short-period Saturn-mass planets, a phenomenon referred to as the “hot-Saturn desert.” This observational scarcity can be utilized to validate the theories regarding the formation and evolution of gas planets. In this study, we conduct large-scale numerical simulations to explore how the initial conditions of gas planets orbiting solar-type and M-dwarf stars influence their evolutionary trajectories in the semimajor axis versus planetary radius (a-R) parameter space. We generate a synthetic population of 10,000 short-period gaseous planets by systematically varying their initial planetary masses (M_p), initial planetary luminosities (L_p), initial core mass fractions (${f}_{{\rm{core}}}$), and semimajor axes (a). Furthermore, we assume these gaseous planets have ceased orbital migration and model their long-term thermal evolution, taking into account the impacts of atmospheric evaporation. Our results show that the initial M_p, L_p, and ${f}_{{\rm{core}}}$ are the dominant factors controlling radius evolution for short-period gas planets. The key to survival as a hot-Saturn analog appears to be having just the right combination of properties after gas disk dissipation: an M_p below 0.5 Jupiter mass (M_Jup), a substantial ${f}_{{\rm{core}}}$ of ≥30%, and relatively low L_p on the order of 10^–6 solar luminosity (L_⊙) or less. The survival criteria for hot-Saturn analogs align with theoretically unfavorable initial conditions of gas planets formed via core accretion scenario, naturally explaining the observed boundaries of the hot-Saturn desert.