99942 Apophis (, previously known by its
provisional designation ) is a
near-Earth asteroid that caused a brief period of concern in December 2004 because initial observations indicated a probability of up to 2.7% that it would hit
Earth on April 13, 2029. Additional observations provided improved predictions that eliminated the possibility of an
impact on Earth or the
Moon in 2029. However, a possibility remained that during the 2029 close encounter with Earth, Apophis would pass through a
gravitational keyhole, a small region no more than about 800 m (~0.5 mi) wide, that would set up a future impact exactly seven years later, on April 13, 2036. This possibility kept it at Level 1 on the
Torino impact hazard scale until August 2006, when the probability that Apophis would pass through the keyhole was determined to be very small. During the short time when it had been most concerning, Apophis set the record for highest rating on the Torino scale, reaching level 4.