Asteroid Apophis From Past, Present And Future Observations

International audienceSince its discovery in 2004, asteroid (99942) Apophis became a study case. It was the first asteroid to have reached the level 4 on Torino scale for a possible collision with the Earth in 2029. Since, new optical and radar data enabled to remove the 2029-threat. Some impacts are still possible in the future but with lower probability. As a matter of fact, some regions located in the target plane of Apophis in 2029 are called keyholes because they are small regions where the asteroid has to pass in order to collide the Earth in the future. Those keyholes can be qualified as primary when they are spawned by one close encounter, and secondary when they are spawned by two consecutives close encounters. The impact probability is directly linked to the size of the uncertainty on the location of Apophis on 2029 but also to the location and size of keyholes. Besides, some other sources of uncertainty, mainly the Yarkovsky effect can also slightly modify this probability (see table below). This non gravitational effect, leading to a secular semi-major axis drift, is poorly known for Near-Earth asteroids in general because it depends on physical values. Thus, it is difficult to compute the accurate influence of this effect. We propose in this work to study the keyholes location versus the size of the ellipse uncertainty. This will involve several orbit propagation of orbital solution from various sets of observations from past and present data, including also a Yarkovsky model. Moreover, we will analyse the contribution of future space data from the Gaia mission which will provide unprecedented observations