From Wikipedia:
99942 Apophis (pronounced /əˈpoʊfɪs/, 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 relatively large probability (up to 2.7%) that it would strike the Earth in 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth or the Moon in 2029. However there remained a possibility that during the 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole, a precise region in space no more than about 400 meters across, 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. It broke the record for the highest level on the Torino Scale, being, for only a short time, a level 4, before it was lowered.[4]
Additional observations of the trajectory of Apophis revealed the "keyhole" would likely be missed and on August 5, 2006, Apophis was lowered to a Level 0 on the Torino Scale. As of October 19, 2006, the impact probability for April 13, 2036, is estimated at 1 in 45,000. An additional impact date in 2037 has been identified; however, the impact probability for that encounter is 1 in 12.3 million.
Despite the fact that there is no longer any significant probability of an Earth impact, the Planetary Society is offering $50,000 in prize awards for a few of the best plans to put a tracking device on or near the asteroid.
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