Reassessing possibly doomed worlds

The first exoplanet with a decaying orbit, WASP-12 b, was observed to not follow a linear transit ephemeris after eight years of observational data (Maciejewski et al. 2016). In the decade since that discovery, at least 18 other planets have been presented with evidence of varying quality for decreasing orbital periods, and thus possible orbital decay, although none has yet proven as compelling as WASP-12 b. The challenge for detection of orbital decay is that it is a small signal that takes years to build up over repeated observations, and by necessity data from many instruments and research groups must be combined. Deep dives into several initially promising systems have led instead to the identification of errors in the published literature (Adams et al. 2024) and the elimination of some candidates.

 

We report on the ongoing efforts of the Short Period Planet Group (SuPerPiG) to monitor over 70 ultra-hot Jupiters for signs of orbital decay. New data include hundreds of new midtimes derived from ground-based transit observations and from TESS observations where available. These are combined with data from the literature and from citizen scientists, such as the Exoplanet Transit Database (ETD). A careful literature review has been conducted for some promising systems, with the goal of creating a cleaned archival data set so that exoplanets that are likely to exhibit orbital decay may continue to be monitored for decades to come. We find that most ultra-hot Jupiters do not exhibit orbital decay, including a sizeable population that would have detected WASP-12 b like decay if it were happening. We also present the most promising systems for long-term timing deviations using the current data.