Small asteroids with sizes of only about a meter hit the Earth's atmosphere and disintegrate into fireballs around every other week, a map released Friday by the US space agency NASA revealed.
The map was based on data gathered by U.S. government sensors from 1994 and 2013, which recorded at least 556 small asteroid impact events, known as fireballs or bolides.
Describing these small impact events as "frequent and random," NASA stressed in a statement that almost all the asteroids disintegrate in the atmosphere and "are usually harmless."
The notable exception, it said, was the Chelyabinsk event on Feb. 15, 2013, which was the largest asteroid to hit the Earth in this period and caused concerns on the potential hazards of small asteroid impacts.
This small asteroid that exploded in the atmosphere near Chelyabinsk, Russia, was believed to be about 20 meters in size before it hit the Earth.
The map dwarfs a database of small impacts based on infra-sound detections released last fall, but it does not contain objects less than a meter in size that impacted the Earth during this period, said NASA.
"The new data could help scientists better refine estimates of the distribution of the sizes of NEOs (near earth objects) including larger ones that could pose a danger to Earth," it said.
The US space agency noted it has increased by a factor of 10 investments in asteroid detection, characterization and mitigation activities over the last five years. The agency said the risk of future impacts should not be taken lightly, citing studies of the Earth's history that indicated about once every 5,000 years or so on average an object the size of a football field hits the Earth and causes significant damage.
