99942 Apophis (/əˈpɒfɪs/, previously known by its provisional designation 2004 MN4) 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 in 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 (half a mile) wide, that would set up a future impact on April 13, 2036. This possibility kept the asteroid 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.
The diameter of Apophis is approximately 325 metres (1,066 ft). As of May 6, 2013 (April 15, 2013 observation arc), the probability of an impact on April 13, 2036 has been eliminated. Preliminary observations by Goldstone radar in January 2013 effectively ruled out the possibility of an Earth impact by Apophis in 2036. Of objects not recently observed, there are about ten asteroids with a more notable Palermo Technical Impact Hazard Scale than Apophis. On average, an asteroid the size of Apophis (325 meters) can be expected to impact Earth about every 80,000 years.