[This article is taken from the April 28 issue of the RocketSciRick Update.]
Evidence has been increasing that the Earth has been pelted by asteroids more frequently that originally thought. In February 2013, an asteroid exploded over Chelyabinsk, Russia, injurying over 1,000 people – an event thought to happen roughly every 100 to 200 years. Then in November, scientists raised the estimate to once every decade or so. Finally, a few days ago, evidence from the Nuclear Test Ban Treaty Organization was presented of major detonations in the atmosphere. Except they weren’t from nuclear explosions; the network had detected airbursts of asteroids in the atmosphere.
According to the B612 Foundation 26 asteroid explosions have been detected since 2001. These ranged from 1 to 600 kilotons of TNT equivalent. For comparison, the explosion on Hiroshima was 15 kilotons. The 2013 explosion over Chelyabinsk was rated at 500 kilotons. The 1908 explosion of Tunguska, in Siberia, was in the range of megatons.
Ed Lu, a former astronaut and CEO of the B612 Foundation, said that “while most large asteroids with the potential to destroy an entire country or continent have been detected, less than 10,000 of the more than a million dangerous asteroids with the potential to destroy an entire major metropolitan area have been found by all existing space or terrestrially-operated observatories.”
“Because we don’t know where or when the next major impact will occur,” he said, “the only thing preventing a catastrophe from a ‘city-killer’ sized asteroid has been blind luck.”
The B612 Foundation has embarked on the Sentinel space telescope project to improve the detection of asteroids. Scheduled for launch in 2018, it expected to uncover 90 percent of asteroids larger than 140 meters across entering the Earth’s region of the solar system. It will also detect many as small as 30 meters across. The Chelyabinsk asteroid was 20 meters across and weighed 13,000 metric tons.
Jet Propulsion Laboratory has been building a catalog of asteroid impacts that may occur during the next century. Known as the Sentry Risk Table, it classifies asteroids by impact probabilities and likely size of the explosion, and provides possible impact dates. At the moment, no major explosions with any significant probability are on the list of 460+ objects. Then again, Chelyabinsk was not on the list. (But that was only 20 meters across.)