The Fate of Exomoons Around Hot Jupiters
Despite extensive searches, no exomoon has been confirmed. Cold gas giants are expected to host moons, while hot Jupiters (HJs), which migrate inward from distant formation sites, provide dynamically hostile environments for moons. In this paper, we systematically investigate the ultimate fate of exomoons around gas giants undergoing two primary migration mechanisms: disk migration and coplanar high-eccentricity migration (CHEM). Through $N$-body simulations using REBOUND, we find that during disk migration, retrograde moons exhibit a significantly higher survival fraction ($\sim 25\%$) compared to prograde ones ($\sim 8\%$). Conversely, for systems that successfully evolve into hot Jupiters via CHEM, no moons can survive the extreme orbital excitation; they are inevitably engulfed or gravitationally stripped before the inward migration. Interestingly, massive exomoons ($\sim 10\,M_{\oplus}$) can exert a strong dynamical feedback on the host planet, acting as a dynamical shield that completely halts the high-eccentricity migration process to form HJs in $\sim 30\%$ of cases, preserving the satellite system. Furthermore, during chaotic multi-body interactions, $\sim 10\%$ of gas giants are dynamically ejected as free-floating planets (FFPs), with roughly $40\%$ of these ejected planets successfully retaining their moons. Combining these dynamical instabilities with severe physical barriers such as atmospheric stripping and magnetic torques, we conclude that mature hot Jupiters are generally devoid of observable primordial moons. Consequently, future observational missions aiming to detect exomoons should focus on cold Jupiters and FFPs, which offer a more stable environment for moon retention.