Refined physical properties of (99942) Apophis from the 2021 observation campaign

We present refined physical properties of the potentially hazardous asteroid (99942) Apophis based on an extensive photometric and spectroscopic observing campaign during its 2021 apparition. The campaign, conducted from January to April 2021, involved 32 facilities in 16 countries and provided dense temporal coverage over 218 nights. Using the light curve inversion method for non-principal axis rotation, we derived an updated convex shape model and spin state. Spectroscopic observations confirm that Apophis generally exhibits spectral characteristics of the S-complex; however, rotational phase-dependent variations in the reflectance spectra show features ranging from Sq-type to Q-type, suggesting subtle surface heterogeneity. These spectral differences, observed across multiple rotational phases, may reflect local resurfacing events, inhomogeneous surface composition, differences in regolith particle size, or the nature of Apophis as a contact binary. Our results provide a constrained pre-encounter baseline for assessing potential surface changes after the 2029 Earth flyby. Updated model parameters and phase-resolved reflectance spectra are provided to serve as a reference for future observations during and after the planetary encounter.