Transits of Inclined Exomoons - Hide and Seek and an Application to Kepler-1625

Abstract

A Neptune-sized exomoon candidate was recently announced by Teachey & Kipping, orbiting a 287 day gas giant in the Kepler-1625 system. However, the system is poorly characterized and needs more observations to be confirmed, with the next potential transit in 2019 May. In this Letter, we aid observational follow up by analyzing the transit signature of exomoons. We derive a simple analytic equation for the transit probability and use it to demonstrate how exomoons may frequently avoid transit if their orbit is larger than the stellar radius and sufficiently misaligned. The nominal orbit for the moon in Kepler-1625 has both of these characteristics, and we calculate that it may only transit roughly 40% of the time. This means that approximately six non-transits would be required to rule out the moon's existence at 95% confidence. When an exomoon's impact parameter is displaced off the star, the planet's impact parameter is displaced the other way, so larger planet transit durations are typically positively correlated with missed exomoon transits. On the other hand, strong correlations do not exist between missed exomoon transits and transit timing variations of the planet. We also show that nodal precession does not change an exomoon's transit probability and that it can break a prograde-retrograde degeneracy.

Accepted at ApJ Letters

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Cited by in corpus (11)

• Orbital Stability of Exomoons and Submoons with Applications to Kepler 1625b-I
• Exploring formation scenarios for the exomoon candidate Kepler 1625b I
• Transit Origami: A Method to Coherently Fold Exomoon Transits in Time Series Photometry
• Transit Light-curves for Exomoons: Analytical Formalism
• Kepler-1708 b-i is likely undetectable with HST
• Analytic Light Curve for Mutual Transits of Two Bodies Across a Limb-darkened Star
• Identifying Potential Exomoon Signals with Convolutional Neural Networks
• On the Stability of Additional Moons Orbiting Kepler-1625 b
• The Dynamics of Co-orbital Giant Exomoons -- Applications for the Kepler-1625 b and Kepler-1708 b Satellite Systems
• Accounting for Transit Timing Detectability: Biases in Planetary Radius and Orbital Period
• The Number of Transits Per Epoch for Transiting Misaligned Circumbinary Planets