Vol. 588
In section 1. Letters

Departure from the constant-period ephemeris for the transiting exoplanet WASP-12 b

by G. Maciejewski, D. Dimitrov, M. Fernandez, et al. A&A 588, L6

Hot Jupiters, those massive planets that orbit with periods of a few days, have tidal interactions with their host stars and consequently are expected to spiral in as orbital angular momentum is transferred to stellar spin. This predicted spiraling-in has never been observed, in part because it starts very slowly and the fast final evolution phase is conversely very short. Using precise new transit timing measurements of WASP-12 b, one of the shortest-period hot Jupiters, Maciejewski et al. find, with a 5-sigma significance, that its period is accelerating and that the system has been found in the final million years of its spiraling-in. This constrains the tidal quality factor of the star, which is at the low end of the theoretical predictions range.