# Could there be an undetected inner planet near the stability limit in Kepler-1647?

## TL;DR

This study investigates the possibility of an undetected inner planet near the stability limit of Kepler-1647, using transit probability and timing variations, concluding such a planet is unlikely to exist.

## Contribution

The paper introduces a method to constrain the presence of undetected inner planets near the stability limit of Kepler-1647 using transit and timing variation analysis.

## Key findings

- A $$30M$_{ ext{$} planet near the stability limit is highly unlikely.
- Future TTV observations can further constrain lower-mass undetected planets.
- The large orbital separation of Kepler-1647b challenges inward disk migration theories.

## Abstract

Kepler-1647b is the most recently discovered planet that transits two stars, i.e., a circumbinary planet (CBP). Due to its large orbital separation, Kepler-1647b stands out from the rest of the Kepler CBPs, which mostly reside on much tighter orbits near the stability limit. The large separation of Kepler-1647b challenges inward disk migration as a dominant formation pathway, suggested by the other Kepler CBPs. In this paper, we consider the possibility of an undetected planet near the stability limit by examining observational consequences of such a planet. We calculate the transit probability of the putative planet, transit timing variations (TTVs) of the known planet, and eclipsing timing variations (ETVs) of the host binary caused by the putative planet. We find the presence of a $\gtrsim$30M$_{\oplus}$ inner planet to be highly unlikely near the stability limit. In addition, we provide future TTV observation windows, which will further constrain possible undetected planets with lower masses.