The Exomoon Corridor: Half of all exomoons exhibit TTV frequencies within a narrow window due to aliasing

TL;DR

This paper demonstrates that half of all exomoons produce transit timing variations with short, predictable aliasing periods, offering a new, simple method to identify exomoon candidates amidst other TTV sources.

Contribution

It analytically characterizes the aliasing of exomoon TTVs, revealing a consistent short-period window that aids in exomoon detection and distinguishes it from planet-planet interactions.

Findings

50% of exomoons induce TTVs with 2-4 cycle periods

Aliased TTV periods are predictable and short, regardless of moon population models

Application to Kepler-1625b i supports the method's effectiveness

Abstract

Exomoons are expected to produce potentially detectable transit timing variations (TTVs) upon their parent planet. Unfortunately, distinguishing moon-induced TTVs from other sources, in particular planet-planet interactions, has severely impeded its usefulness as a tool for identifying exomoon candidates. A key feature of exomoon TTVs is that they will always be undersampled, due to the simple fact that we can only observe the TTVs once per transit/planetary period. We show that it is possible to analytically express the aliased TTV periodicity as a function of planet and moon period. Further, we show that inverting an aliased TTV period back to a true moon period is fraught with hundreds of harmonic modes. However, a unique aspect of these TTV aliases is that they are predicted to occur at consistently short periods, irrespective of what model one assumes for the underlying moon population. Specifically, 50% of all exomoons are expected to induce TTVs with a period between 2 to 4 cycles, a range that planet-planet interactions rarely manifest at. This provides an exciting and simple tool for quickly identifying exomoons candidates and brings the TTV method back to the fore as an exomoon hunting strategy. Applying this method to the candidate, Kepler-1625b i, reveals that its TTV periodicity centers around the median period expected for exomoons.