Shape and spin-state model of asteroid (99942) Apophis reconstructed from photometric observations in 2020/21

(99942) Apophis is a near-Earth asteroid that will closely approach to Earth in 2029; the minimum geocentric distance will be about 38,000 km.  During the approach, the spin state of Apophis is expected to be altered by Earth's gravitation torque.  The exact change depends on the orientation of Apophis during the close approach.  Although the shape and spin-state model of Apophis was reconstructed from 2012/13 observations by Pravec et al. (2014, Icarus 233, 48),  the precision of rotation parameters they derived was not sufficient to predict the orientation for 2029.

We will present our analysis of photometric observations of Apophis that we carried out from 2020-11-16 to 2021-05-06 with the 1.54-m Danish telescope at La Silla.  By applying the lightcurve inversion technique of Kaasalainen (2001, A&A 376, 302), we reconstructed the spin state and shape of Apophis.  This new model agrees with the one reconstructed by Pravec et al. (2014) and with an updated model published by Lee et al. (2022, arXiv:2204.02540).  We aimed to invert both the 2012-2013 and 2020-2021 data together and reconstruct the Apophis spin state with high precision.  The long interval of observations would enable us to precisely determine the rotation and precession periods and thus reliably predict  the orientation of Apophis during its 2029 flyby, calculate a change of its spin state, and predict how the Yarkovsky effect will influence  the post-encounter orbit of Apophis, which is crucial for its post-2029 impact predictions.