Princeton University Extrasolar Planet Discussion Group

Transit timing variations (TTVs) are ubiquitous in exoplanet transit datasets, with Kepler alone containing ~2,000 periodic TTVs. However, these TTVs are often ambiguous from a model selection perspective, as it is difficult to determine the physical cause of a TTV, be it another planet, a moon, or stellar activity. Currently, careful considerations must be taken, on a case-by-case basis, using computationally expensive N-body simulations, in order to determine the cause of an observed TTV signal. In this talk, we will discuss our work building TTV model selection techniques, through investigations of the orbital landscape of exoplanet TTVs. Specifically, we will focus our discussion on two primary areas: the exomoon corridor and the exoplanet edge. The exomoon corridor ranges from two-to-four times the orbital period of the transiting planet, and is where we expect a pile-up (~50%) of exomoon induced TTVs near the Nyquist period due to aliasing caused by undersampling. We will share our results from searching the exomoon corridor for moon-like TTVs and our follow-up analysis of one of these systems. We will also present our finding that perturbing planets are not expected to induce a TTV with an observed dominant period less than half their own orbital period. This “exoplanet edge” is the manifestation of an observational alias of the true TTV period. The presence of an anomalous dominant TTV period, in a two-planet system, that falls below the exoplanet edge would demonstrate that there exists additional mass in the system, besides the two known exoplanets. Finally, we identify a number of two-planet systems, in Kepler data, that don't lie on the exoplanet edge, and discuss several possible explanations for additional mass in the system.