Rotation P_ψ and precession P_ϕ periods of Apophis before and after the close encounter with Earth in April 2029 calculated from the purely gravitational model of the spin state change. Individual symbols come from 1000 nominal model simulations, with gravitational torques included, using statistically equivalent initial conditions on January 1, 2021. The three colors identify solutions starting from the three statistically equivalent initial solutions (compare with Fig. 1): red for the B-group, blue for the A-group, and green for the C-group. The right panel shows the current accuracy of the Apophis solution from the combination of the 2012-2013 and 2020–2021 observations. Those data are also reproduced in the left panel, but with a larger abscissa and ordinate scale, they are resolved only as single dots. The post-encounter P_ϕ and P_ψ values, spread over a large region, are shown on the left panel only. As expected, the uncertainty interval in both quantities expands by a factor larger than 10³. The post-encounter median P_ϕ value decreases to ≃25.75 h, while the median P_ψ value remains about the same.