Prospects for detecting hot-Jupiter tidal decay through transit timing with the mission Earth 2.0

Abstract

Orbital decay of hot Jupiters provides a unique opportunity to probe tidal dissipation in star-planet systems. However, despite extensive observational efforts, only one hot Jupiter, namely WASP-12b, currently exhibits conclusive observational evidence for orbital decay. Expanding this sample is therefore crucial for establishing a statistical understanding of tidal interactions in planetary systems. Long-term transit timing variations (TTVs) provide a direct observational probe of orbital decay induced by tidal dissipation between a hot Jupiter and its host star. The Earth 2.0 (ET) mission will revisit the original Kepler field, delivering high-precision transit timing measurements and extending the observational baseline to approximately 24 years (2009--2033). In this work, we aim to assess the capability of ET to detect orbital decay in hot Jupiters previously observed by Kepler. We generate four years of simulated ET light curves based on the expected photometric precision and observing cadence of the mission and analyze them jointly with archival Kepler and TESS observations. Using these combined datasets, we perform long-term TTV analyses and predict the achievable precision for measuring orbital period variations. We find that ET can substantially improve the precision of orbital decay measurements in hot Jupiter systems by a factor of 7.2. Assuming the stellar tidal quality factor inferred from previous observations, ET is expected to detect orbital decay in three additional hot Jupiter systems. The expanded sample of hot Jupiters with measured orbital decay will establish ET as a powerful probe of tidal dissipation in star-planet systems, providing tighter constraints on stellar tidal quality factors and new insights into the tidal evolution of hot Jupiters.