section_path: Threats to Earth
section_name: Threats to Earth
paragraph_text: Threats to Earth
  
  There is increasing interest in identifying asteroids whose orbits cross Earth 's, and that could, given enough time, collide with Earth. The three most important groups of near-Earth asteroids are the Apollos, Amors, and Atens.
  
  The near-Earth asteroid 433 Eros had been discovered as long ago as 1898, and the 1930s brought a flurry of similar objects. In order of discovery, these were: 1221 Amor, 1862 Apollo, 2101 Adonis, and finally 69230 Hermes, which approached within 0.005 AU of Earth in 1937. Astronomers began to realize the possibilities of Earth impact.
  
  Two events in later decades increased the alarm: the increasing acceptance of the Alvarez hypothesis that an impact event resulted in the Cretaceous–Paleogene extinction, and the 1994 observation of Comet Shoemaker-Levy 9 crashing into Jupiter. The U.S. military also declassified the information that its military satellites, built to detect nuclear explosions, had detected hundreds of upper-atmosphere impacts by objects ranging from one to ten meters across.
  
  All of these considerations helped spur the launch of highly efficient surveys, consisting of charge-coupled device (CCD) cameras and computers directly connected to telescopes. As of 2011, it was estimated that 89% to 96% of near-Earth asteroids one kilometer or larger in diameter had been discovered. As of 29 October 2018, the LINEAR system alone had discovered 147,132 asteroids. Among the surveys, 19,266 near-Earth asteroids have been discovered including almost 900 more than 1 km (0.6 mi) in diameter.
  
  In June 2018, the National Science and Technology Council warned that the United States is unprepared for an asteroid impact event, and has developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare. According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched.