The Narrow Formation Pathway of Hot Saturns: Constraints on Initial Planetary Properties
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-s...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/adddb3 |
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| Summary: | 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. |
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| ISSN: | 1538-4357 |