Ploonets: formation, evolution, and detectability of tidally detached exomoons

Abstract

Close-in giant planets represent the most significant evidence of planetary migration. If large exomoons form around migrating giant planets which are more stable (e.g. those in the Solar System), what happens to these moons after migration is still under intense research. This paper explores the scenario where large regular exomoons escape after tidal-interchange of angular momentum with its parent planet, becoming small planets by themselves. We name this hypothetical type of object a ploonet. By performing semi-analytical simulations of tidal interactions between a large moon with a close-in giant, and integrating numerically their orbits for several Myr, we found that in ∼50 per cent of the cases a young ploonet may survive ejection from the planetary system, or collision with its parent planet and host star, being in principle detectable. Volatile-rich ploonets are dramatically affected by stellar radiation during both planetocentric and siderocentric orbital evolution, and their radius and mass change significantly due to the sublimation of most of their material during time-scales of hundred of Myr. We estimate the photometric signatures that ploonets may produce if they transit the star during the phase of evaporation, and compare them with noisy lightcurves of known objects (Kronian stars and non-periodical dips in dusty lightcurves). Additionally, the typical transit timing variations (TTV) induced by the interaction of a ploonet with its planet are computed. We find that present and future photometric surveys' capabilities can detect these effects and distinguish them from those produced by other nearby planetary encounters.

Survival of Exomoons Around Exoplanets

“…Our results are in line with those of Sucerquia et al (2019), too, who concluded that long-period planets are more favorable moon hosts than short-period ones. They used a very similar calculation method with the aim of estimating the TTV and TDV signals for detection.…”

Can close-in giant exoplanets preserve detectable moons?

“…However, the synthetic population of moons explored in this work has shown that few of them are within the sensitivity limit of Kepler and TESS (see Figs 7 and 8). Notwithstanding that the detection probability of these moons is low owing to their small size and short a stop , all of them would be detectable with Kepler if we use Transit Timing Variation (TTV) signals, but their existence has to be confirmed with other methods since TTVs can also arise due to interactions with other planets in the system (even with previously detached exomoons or ploonets; Sucerquia et al 2019).…”

“…In Fig. 3 we show the fraction of exomoons (n) attached (surviving tidal migration) and detached (mostly ploonets; Sucerquia et al 2019) from its host planet after 4.5 Gyr evolution, respect to the total number of moons (n total ) and as a function of planetary semi-major axis. It can be seen that the chance for a satellite to survive increases with a p .…”

“…Several authors have proposed different mechanisms to explain the depletion of moons on relatively short time-scales around close-in planets. Some of them include: secular and resonant perturbations (Barnes & O'Brien 2002;Spalding et al 2016); planet scattering (Hong et al 2018); and tidal detachment (Sucerquia et al 2019;Martinez et al 2019).…”

Cronomoons: origin, dynamics, and light-curve features of ringed exomoons

“…Zuluaga et al 2015 and references therein). Also, the magnitude and detectability of TTV and TDV signals for different theoretical populations of exomoons have been constrained (Sucerquia et al 2019(Sucerquia et al , 2020a and delimited in terms of the semi-major axes and masses of systems of moons, indicating that any TTVs or TDVs larger than these constrained values must have a different origin.…”