Non-zero Yarkovsky acceleration for near-Earth asteroid (99942) Apophis

The leading source of uncertainty to predict the orbital motion of asteroid (99942) Apophis is a non-gravitational acceleration arising from the anisotropic thermal re-emission of absorbed radiation, known as the Yarkovsky effect. Previous attempts to obtain this parameter from astrometry for this object have only yielded marginally small values, without ruling out a pure gravitational interaction. Here we present an independent estimation of the Yarkovsky effect based on optical and radar astrometry which includes observations obtained during 2021. Our numerical approach exploits automatic differentiation techniques. We find a non-zero Yarkovsky parameter, A 2 = (−2.899 ± 0.025) × 10 −14 au d −2 , with induced semi-major axis drift of (−199.0 ± 1.5) m yr −1 for Apophis. Our results provide definite collision probability predictions for the close approaches in 2029, 2036, and 2068.