The Orbit of WASP-12b is Decaying

TL;DR

This paper provides strong evidence that the orbit of the exoplanet WASP-12b is decaying due to tidal interactions, with new observations confirming the decay and ruling out alternative explanations.

Contribution

The study presents new transit, occultation, and radial-velocity data that conclusively demonstrate orbital decay in WASP-12b, establishing it as the first confirmed decaying exoplanet orbit.

Findings

Orbital decay timescale is approximately 3.25 million years.

Decay is due to tidal dissipation, not the R{\

Abstract

WASP-12b is a transiting hot Jupiter on a 1.09-day orbit around a late-F star. Since the planet's discovery in 2008, the time interval between transits has been decreasing by $29\pm 2$ msec year$^{-1}$. This is a possible sign of orbital decay, although the previously available data left open the possibility that the planet's orbit is slightly eccentric and is undergoing apsidal precession. Here, we present new transit and occultation observations that provide more decisive evidence for orbital decay, which is favored over apsidal precession by a $\Delta\mathrm{BIC}$ of 22.3 or Bayes factor of 70,000. We also present new radial-velocity data that rule out the R{\o}mer effect as the cause of the period change. This makes WASP-12 the first planetary system for which we can be confident that the orbit is decaying. The decay timescale for the orbit is $P/\dot{P} = 3.25\pm 0.23$ Myr. Interpreting the decay as the result of tidal dissipation, the modified stellar tidal quality factor is $Q'_\star = 1.8 \times10^{5}$.