![WASP-12 b: A Planet Falling Into Its Star](https://cdn.slatesource.com/b/c/6/bc631f42-56fa-4ba9-8c35-040ff7b11204.webp) # WASP-12 b: A Planet Falling Into Its Star - [Made in Slatesource](https://slatesource.com/@steph/wasp-12-b-a-planet-falling-into-its-star) - By [Steph](https://slatesource.com/@steph) - Created on Sep 19, 2026 ## The first planet we have watched begin to die Most of what we know about planetary death is inference. WASP-12 b is the exception: it is measurably falling into its star, and the measurement is a clock. Every transit arrives slightly earlier than the last, and across more than a decade of timings the interval between them is shrinking by 29 milliseconds per year. Orbital decay was favoured over the competing explanation of apsidal precession by a Bayes factor of 70,000, which is about as close to settled as this kind of observation gets. Orbital decay 29 plus or minus 2 milliseconds per year One year 1.091 Earth days Radius 22.0 Earth radii, nearly 2 Jupiters Host star WASP-12 at 6265 K and 1.69 solar radii Orbit radius 0.023 AU, inside where most planets survive Distance about 1393 light-years journey·5 Stages # How a hot Jupiter dies Damage / Stage "Orbiting this close, the planet raises a tidal bulge on the star itself, and the star raises one on the planet. "The planet is stretched into an egg. It is no longer a sphere in any useful sense. "Gas streams off the leading end and feeds back onto the star, which is visible in the ultraviolet. "Tidal friction removes orbital energy. Transits arrive 29 ms earlier each year, and the rate accelerates as the orbit tightens. "On the current rate, roughly three million years until the planet is inside the star. 🪐⏱️💀01.01.2008 – 01.12.2020 01.01.2008Discovered by the WASP survey, one of the shortest-period hot Jupiters then known and already visibly distorted by its star's gravity. 01.01.2008 01.11.2019Transit timings across eleven years show the orbit is decaying rather than precessing, favoured by a Bayes factor of 70,000. 01.11.2019 01.12.2020TESS observations independently confirm the shortening period, ruling out an instrument artefact in the earlier dataset. 01.12.2020 Three million years is the headline and it deserves a caveat. It is what you get by extrapolating the current decay rate forward, and the rate itself depends on how efficiently the star dissipates tidal energy, a quantity that is poorly known and probably not constant as the orbit tightens. The measurement that the orbit is shrinking is solid. The date of death is an extrapolation. The archive has no equilibrium temperature for this planet, so the figure on the cover is derived from the star's output and the orbital distance and carries an asterisk. Everything here rests on timing, not imaging. Nobody has seen the planet deform or the stream of gas directly. What was measured is that transits keep arriving early, by an amount you could not notice without a decade of data. [The Orbit of WASP-12b is Decaying](https://arxiv.org/abs/1911.09131?utm_source=slatesource)