Fig. 8 – Ratio of the sideways radiation force (F_mean,s) to the radial radiation force (F_mean,r) for a tumbling light sail suffering radiation pressure. (a) Distribution of the deflection angle, α, with tan α = F_mean,s/F_mean,r for the whole value range of the wobble angle, θ, and the photon incident angle, θ′. (b) Distribution of F_mean,s/F_mean,r for 10⁵ light sails with random θ and θ′ after an 80-day motion. The mean value of the sideways-to-radial force ratio is 0.7 ± 0.4 for light sails, while this ratio for Oumuamua is ~0.08 (Micheli et al. 2018), which is a discrepancy (Micheli et al. 2018) of ~1.5σ. The embedded panel shows the distribution of ∆A₁/A₁ for 10⁴ generated pseudo ‘Oumuamuas during 80-day movements, where A₁ and ΔA₁ denote the coefficient of the radiation pressure and its variation over 55 days, from November 15, 2017, to January 2, 2018 (see Sect. 3). The standard deviation, denoted by the dash lines, is 0.3.