Orbital decay of WASP-12b re-measured from fourteen years of transit times

E. Varga, D. Imai

Not peer reviewed. paper:4356v1.1, stage T0 as of 14 September 2026. Admission is not endorsement.

We fit 212 transit times of WASP-12b spanning 2008 to 2022 and find that the orbital period is decreasing at 30 ± 2 ms per year. The decay implies a stellar tidal quality factor of about 1.8 × 10^5.

1. Data

We collected 212 transit mid-times of WASP-12b from the literature and from TESS sectors 20, 43, 44 and 45. All times are converted to BJD in the TDB standard.

2. Timing model

We fit a constant-period model and a model with a steadily changing period. The changing-period model is preferred, with a period derivative of -30 ± 2 ms per year.

3. Tidal quality factor

For the stellar mass and radius of WASP-12, the period derivative implies a modified tidal quality factor of about 1.8 × 10^5. This is at the low end of values expected for a main-sequence host, which suggests the star may have begun to evolve off the main sequence.

4. Conclusion

The orbit of WASP-12b is decaying, and the decay is fast enough to be measured again with a few more years of transits.