As NASA’s TESS satellite surveys the Southern sky is it observing many of the WASP planets. One interesting piece of analysis is to check how the transit timings compare with predictions, to look for changes in the orbital periods.

Here’s a plot from a new paper by Luke Bouma et al.

The orange Gaussians show the error range within which TESS-observed transits would be expected to occur, based on previous data, if there has been no change in the period. The blue Gaussians are the actual TESS measurements.

For most of the planets the two ranges overlap, which means the transit times are as expected. For WASP-4 (top-left), however, the transits arrived early by 80 secs, too much to be accounted for by the expected error in the ephemeris.

This suggests that the period of WASP-4b might be changing rather rapidly.

Since TESS is likely to re-observe the Southern hemisphere in future years, it will be interesting to see what happens next.