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

## TL;DR

This paper investigates the formation, evolution, and potential detectability of tidally detached exomoons, called ploonets, which may become small planets after escaping their parent planets around close-in giant exoplanets.

## Contribution

It introduces the concept of ploonets, models their tidal interactions and orbital evolution, and assesses their detectability through photometric signatures and transit timing variations.

## Key findings

- Approximately 50% of large moons may become detectable ploonets after ejection or collision.
- Volatile-rich ploonets undergo significant mass loss due to stellar radiation over hundreds of Myr.
- Photometric signatures and TTVs of ploonets could be detectable with current and future surveys.

## 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 \textit{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 $\sim$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.