[en] Photometric observations of the asteroid (99942) Apophis taken from December 2012 to April 2013 revealed that it is in a non-principal axis rotation state. We constructed a numerical model of the asteroid's shape and rotation. The asteroid is in a short-axis mode (SAM) of excited rotation. The precession and rotation periods are P_φ = 27.38 ± 0.07 h and P_ψ = 263 ± 6 h, respectively. The rotation is retrograde with the angular momentum vector's ecliptic longitude and latitude of 250° and -75° (the uncertainty area is approximately an ellipse with the major and minor semiaxes of 27° and 14°, respectively). The shape of the asteroid is dynamically close to a prolate ellipsoid, with the lengths of largest and intermediate axes of 1.64 ± 0.09 and 1.14^{+0.04}_{-0.08}, respectively (the shortest axis is normalized to unity); the largest and intermediate moments of inertia differ by 3-4
Manfroid, Jean ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)
Opitom, Cyrielle ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Gillon, Michaël ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
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