Thursday, August 24, 2017

Hot Jupiter WASP-12b's Orbit is Decaying

The Apparently Decaying Orbit of WASP-12b


Patra et al


We present new transit and occultation times for the hot Jupiter WASP-12b. The data are compatible with a constant period derivative: $\dot{P}=-29\pm 3$ ms yr−1 and $P/\dot{P}=3.2\,\mathrm{Myr}$. However, it is difficult to tell whether we have observed orbital decay or a portion of a 14-year apsidal precession cycle. If interpreted as decay, the star's tidal quality parameter ${Q}_{\star }$ is about $2\times {10}^{5}$. If interpreted as precession, the planet's Love number is 0.44 ± 0.10. Orbital decay appears to be the more parsimonious model: it is favored by ${\rm{\Delta }}{\chi }^{2}=5.5$ despite having two fewer free parameters than the precession model. The decay model implies that WASP-12 was discovered within the final ~0.2% of its existence, which is an unlikely coincidence but harmonizes with independent evidence that the planet is nearing disruption. Precession does not invoke any temporal coincidence, but it does require some mechanism to maintain an eccentricity of $\approx 0.002$ in the face of rapid tidal circularization. To distinguish unequivocally between decay and precession will probably require a few more years of monitoring. Particularly helpful will be occultation timing in 2019 and thereafter.

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