(99942) Apophis is an Aten-type asteroid, which will make a very close approach to our planet on April 13, 2029, passing within less than 40,000 km, close to the ring of geostationary satellites. Its size is about 375 m and its rotation period 30.6 h. This close approach will change the orbit substantially, from Aten type to Apollo.
Apophis was discovered on June 19, 2004 by R. A. Tucker, D. J. Tholen, and F. Bernardi at Kitt Peak. It was temporarily lost and rediscovered in December 2004. Shortly thereafter, the close approach in 2029 was realized; even a collision at that time was possible. This has been ruled out based on extensive observations, including radar; the orbital evolution after 2029 is still uncertain allowing an impact probability of 5.7 × 10−6 (see impact monitoring sites at JPL and the University of Pisa).