99942 Apophis

99942 Apophis (provisional designation 2004 MN4) is a near-Earth asteroid and a potentially hazardous object, 450 metres (1,480 ft) by 170 metres (560 ft) in size. During a brief period of concern in December 2004, initial observations indicated a probability of 2.7% that the asteroid would hit Earth on Friday, April 13, 2029. Later observations eliminated that possibility of an impact with Earth, and it will pass Earth in 2029 at a distance of about 31,600 km (19,600 mi) above the surface. It will also have a close encounter with the Moon, passing about 89,600 km (55,700 mi) from the lunar surface.

A small possibility remained that during its 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole estimated to be 800 kilometres in diameter, which would have set up a future impact exactly seven years later on Easter Sunday, 13 April 2036. This possibility kept it at Level 1 on the 0 to 10 Torino impact hazard scale until August 2006, when the probability that Apophis would pass through the keyhole was determined to be very small and Apophis's rating on the Torino scale was consequently lowered to Level 0. By 2008, the keyhole had been determined to be less than 1 km wide. During the short time when it had been of greatest concern, Apophis set the record for highest rating ever on the Torino scale by reaching Level 4 on 27 December 2004.