学术文献库

On April 13, 2029, asteroid Apophis will pass within six Earth radii ($\sim$31000 km above surface), in the closest approach of this asteroid in recorded history. This event provides unique scientific opportunities to study the asteroid, its orbit, and surface characteristics at an exceptionally close distance. In this paper we perform a synthetic geometrical, geographical and temporal analysis of the conditions under which the asteroid can be observed from Earth, with a particular emphasis on the conditions and scientific opportunities for bistatic radar observations, the most feasible radar technique applicable during such a close approach. For this purpose, we compile a list of present and future radio observatories around the globe which could participate in bistatic radar observation campaigns during the closest approach of Apophis. We estimate signal-to-noise ratios, apparent sky rotation, surface coverage and other observing conditions. We find that a global collaboration of observatories across Australia, Africa, Europe and America will produce high-resolution delay-Doppler radar images with signal-to-noise ratios above $10^8$, while covering $\sim$85\% of the asteroid surface. Moreover, if properly coordinated, the extreme approach of the asteroid might allow for radio amateur detection of the signals sent by large radio observatories and citizen science projects could then be organized. We also find that for visual observations, the Canary Islands will offer the best observing conditions during the closest approach, both for professionals as well as for amateurs. The apparent size of Apophis will be 2-3 times larger than typical seeing, allowing for resolved images of the surface.