Apophis

99942 Apophis (provisional designation 2004 MN4) is a near-Earth asteroid classified as a potentially hazardous object. Its mean diameter is about 340–370 metres (1,120–1,210 ft), while radar observations indicate an elongated shape with a long axis of about 450 metres (1,480 ft) and suggest that it may be bilobed. It was discovered on 19 June 2004 by Roy A. Tucker, David J. Tholen, and Fabrizio Bernardi at Kitt Peak National Observatory. The asteroid was numbered 99942 in 2005 and named after Apophis, the Greek name of the ancient Egyptian serpent deity Apep. Apophis attracted widespread attention shortly after its discovery because early orbit calculations indicated a possible collision with Earth on 13 April 2029. The estimated probability reached 2.7% on 27 December 2004, and Apophis was rated level 4 on the Torino scale, the highest rating attained by any object. Later that day, the identification of a precovery image from March 2004 extended the observation arc and eliminated the possibility of a 2029 impact. Small probabilities of impacts on later approaches, including in 2036 and 2068, remained for several years, but increasingly precise observations reduced those risks. In 2021, Apophis was removed from the Sentry Risk Table after an impact during the following 100 years was ruled out. Apophis will nevertheless make an exceptionally close approach to Earth on 13 April 2029, passing about 31,600 kilometres (19,600 mi) above the surface. It is expected to reach magnitude 3.1 and become visible to the naked eye under suitable conditions from parts of Europe, Africa, and western Asia. Earth's gravity will alter its orbit, changing it from an Aten-class asteroid to an Apollo-class asteroid, and tidal forces during the encounter may alter its rotation and partially resurface it. The 2029 encounter has also made Apophis a target for spacecraft exploration. NASA's OSIRIS-APEX, formerly OSIRIS-REx, is planned to rendezvous with Apophis after the Earth encounter and study it for 18 months. The ESA–JAXA Ramses mission is planned to rendezvous with the asteroid before the encounter.