Predicted values of the Yarkovsky effect and density for asteroid (1862) Apollo. Bottom panel: Predicted semimajor axis drift da/dt (ordinate) due to the Yarkovsky effect from our model for three different values of the bulk density (2.5, 2.75, and 3 g cm⁻³; see the labels and the middle curve for 2.75 g cm⁻³) are shown by solid curves. The abscissa is the surface thermal inertia in SI units (J m⁻² s^−0.5 K⁻¹). We assumed the rotation state and shape model from the light-curve inversion in Sect. 2.1, and an effective size of 1.55 km. The grayscale horizontal region shows the value −(1.94 ± 0.16) × 10⁻⁴ au My⁻¹ from the orbit determination. The grayscale vertical region shows the range of the best-fit surface thermal inertia value (see Rozitis & Green 2012). Top panel: Model-predicted bulk density to match the observed value of the semimajor axis drift shown by the grayscale region. The solid line in the middle shows the exact correspondence surrounded by a map of the sigma interval of the Yarkovsky drift. A nominal effective size of 1.55 km is used. If this value were higher or lower, the density solution would shift in the direction indicated by the arrows (preserving the ρ_b D value). The analysis of ten different shape models of (1862) Apollo reveals a variation of ±12% about the median value used in the figure. Effects of small-scale surface roughness, if important, would shift the solution toward a lower value by typically 10–30% (see Rozitis & Green 2012).