A new paper by Jake Turner et al (Cornell University) analyses TESS data on WASP-12b, showing that the transit timings confirm that the orbital period of the planet is getting shorter.
The orbit is changing on a timescale of 3 Myrs — if it continues the planet will spiral into its star on that timescale. The natural interpretation is that the orbital decay is being caused by tides that the gravitational pull of the planet arouses in the host star. We don’t yet properly understand the effect that tides have on the star, or how internal waves created by the tides then dissipate their energy. Thus the observations of WASP-12b point to the need for a better theoretical understanding of stellar interiors.
Of course the period change has only been measured over a decade, and this is vastly shorter than the orbital-decay timescale. Thus it could be that other mechanisms that we don’t know about can cause short-term changes in planet’s orbital periods. Ongoing monitoring of all the WASP hot Jupiters is thus needed to properly understand what is going on. The TESS satellite, which will observe most hot Jupiters every two years or so, on an ongoing basis, is the perfect tool for the task.
Update: Here’s a Twitter thread by the lead author, Jake Turner.
Here’s the latest update on the changes in the orbital period of WASP-12b, from a new paper by Samuel Yee et al.
The times of transit are getting earlier, which means that the period is decreasing slightly. By also considering the times of occultation (when the planet passes behind the star), and also the radial-velocity measurements of the system, the authors deduce that the changes are not the effect of some other planet, but are a real decay in the orbit of WASP-12b. This is expected to occur as a result of tidal interactions between the planet and its host star.
One notable conclusion is that the rate of period decay in WASP-12b is much faster than that in WASP-19b, which shows no detectable period change yet, despite it being an even shorter-period hot Jupiter, which should increase tidal interactions. Yee et al suggest that the difference could arise if the host star WASP-12 is a sub-giant star, whereas WASP-19 is not.
Update: Following an article on WASP-12b’s orbital decay, supplied by Liz Fuller-Wright of Princeton University, and appearing in phys.org and Science Daily, the work has gained media attention from CNN, Science Times, Universe Today, and the UK’s Metro.