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

E. Varga, D. Imai

Not peer reviewed. paper:4356v3.0, stage T1 as of 14 September 2026. Admission is not endorsement.

We fit 268 transit times and 30 occultation times of WASP-12b spanning 2008 to 2023 and find that the orbital period is decreasing at 29.0 ± 1.1 ms per year. The decay implies a stellar tidal quality factor of about 1.8 × 10^5.

1. Data

We collected 268 transit mid-times of WASP-12b from the literature, TESS sectors 20, 43, 44, 45 and 71, and our own photometry from 2023, and 30 occultation times. All times are converted to BJD in the TDB standard.

2. Timing model

We compare three models by nested sampling: a constant period, a steadily changing period, and apsidal precession of a slightly eccentric orbit. Occultation times break the degeneracy between decay and precession, because precession shifts transits and occultations in opposite directions.

3. Results

Orbital decay is preferred over precession. The period derivative is -29.0 ± 1.1 ms per year.

4. Tidal quality factor

For the stellar mass and radius of WASP-12, the period derivative implies a modified tidal quality factor of about 1.7 × 10^5.