Extreme exomoons in WASP-49 Ab: Dynamics and detectability

Context. WASP-49Ab, a low-density Saturn-like planet in a tight orbit around a Sun-like star within a wide binary system, is a compelling candidate for hosting a volcanic moon, as suggested by the detection of Doppler-shifted sodium. Aims. This study evaluates the stability of potential satellites around WASP-49Ab under the influence of planetary oblateness, relativistic effects, and perturbations from a close companion star, focusing on their impact on light curve parameters such as transit duration and impact parameter variations, driven by the evolution of the planet’s orbit in this extreme environment. Methods. Using N-body simulations and semi-analytical methods, we analysed moon’s dynamics across varied initial conditions and gravitational frameworks including the potential of an oblate planet and the effects of the general relativity. Results. We find that ‘selenity’, a moon survival indicator, is high in close orbits with low eccentricity and near the Roche limit, especially for masses higher than Io’s. Stability decreases as eccentricity or distance from the planet increases. Additionally, we observe a strong destabilising resonance near 1.4 Rp when planetary eccentricities are considered to be ≳0. Conclusions. This study confirms the potential for stable exomoons around WASP-49Ab despite its hostile environment, emphasising the importance of incorporating diverse physical effects in stability analyses, aiding future detection efforts.