Asteroid (99942) Apophis: new predictions of Earth encounters for this potentially hazardous asteroid

Context. The potentially hazardous asteroid (99942) Apophis, previously designated 2004 MN4, is emblematic of the study of asteroids that could impact the Earth in the near future. Orbit monitoring and error propagation analysis are mandatory to predict the probability of an impact and, furthermore, its possible mitigation. Several aspects for this prediction have to be investigated, in particular the orbit adjustment and prediction updates when new astrometric data are available. Aims. We analyze Apophis orbit and provide impact predictions based on new observational data, including several orbit propagations. Methods. New astrometric data of Apophis have been acquired at the Pic du Midi one-meter telescope (T1m) during March 2011. Indeed, this asteroid was again visible from ground-based stations after a period of several years of unfavorable conjunction with the Sun. We present here the original astrometric data and reduction, and the new orbit obtained from the adjustment to all data available at Minor Planet Center (until March 2011). Results. We present a new sketch of keyholes and impacts for the next century. Additionally, we discuss observational errors, astrometric reduction, orbit adjustment, and adequacy of the dynamical model used.