Characterizing transit timing and duration variations caused by systemic proper motion

Gravitational interactions between stars and planets, including mutual planet-planet interactions, cause planetary orbits to change with time. Such changes include apsidal or nodal precession, i.e., variations in the alignment of the orbit, as well as deviations in a planet's semi-major axis, eccentricity, or inclination. Over decade-long time periods, those orbital changes give rise to small but detectable observational signatures, especially among short-period planets, such as drifts in the timing and duration of exoplanet transits. If characterized, these secular orbital changes can reveal a wealth of information about exoplanetary systems, including insights into planetary interiors.

However, exoplanet host stars are in constant motion relative to the Sun, gradually altering both their distance from Earth and the apparent orientation of their planetary orbits in the sky. This systemic proper motion introduces additional transit timing and duration variations that could mimic true signatures of orbital evolution, risking misinterpretation of the underlying physical mechanisms. As the number of transiting exoplanets with observations spanning decades continues to grow, it will become increasingly important to determine whether the proper motion of transiting exoplanet host stars plays a significant role in observing secular variations.

Here, we present the first large-scale statistical analysis of proper motion-induced transit timing and duration variations, combining precise astrometric measurements from the Gaia space telescope with stellar and planetary parameters from the NASA Exoplanet Archive for a population of over 4000 transiting exoplanets. We find that in many cases, these secular trends are measurable on decade timescales and can dominate signatures of true dynamical evolution, particularly in the case of transit durations.

The goal of this work is not only to highlight the significance of these effects across the exoplanet population, but also to provide a database to serve as a practical tool for aiding long-term orbit monitoring. In this talk, we provide an update on the project, highlight systems of particular interest, and discuss the broader implications for studies of orbital evolution and ephemeris refinement.