Addressing the lawmakers Bolden said there is an "extremely remote" chance that any of these alien rocks hit Earth in near future, but if a large asteroid big enough to destroy the United States gives a surprise or planned visit there is nothing except praying that could be done to prevent a collision.
"From the information we have, we don't know of an asteroid that will threaten the population of the United States," Bolden said. "But if it's coming in three weeks, pray."
Scientific estimates state that over 10,000 asteroids with the potential to destroy a large city had passed Earth undetected in 2012. Despite the progress achieved in space science and technology, it is not yet possible to map every cosmic rock that brush past Earth.
The meeting was called by House of Representatives Science Committee Chairman Lamar Smith, a Texas Republican to discuss the progress in tracking the near-Earth alien objects and how prepared the federal agencies were to protect the planet, in case of possible space rock collision. The meeting came more than a month after two events raised concern over the safety of Earth from flying space masses, USA Today reported.
A meteor exploded several miles above the Earth, sending sonic shockwaves and showering debris over Chelyabinsk, Russia, Feb. 15. About 1,500 people were injured and hundreds of houses and buildings were damaged by shockwaves generated by the explosion. The Russian meteor was a surprise visitor that caught scientists off-guard and was the largest reported to hit Earth since the meteor that hit the Tunguska region in Siberia in 1908, leveling more than 830 square miles of forest.
Another football field sized asteroid '2012 DA14' passed Earth the same day in a trajectory of about 17,200 miles (27,681 km) from Earth, closer than the network of television and weather satellites that circle the planet.
Both events, though rare, had created a huge panic across the globe.
"An asteroid of that size, a kilometer or bigger, could plausibly end civilization," White House science advisor John Holdren told legislators at the same hearing.
"The odds of a near-Earth object strike causing massive casualties and destruction of infrastructure are very small, but the potential consequences of such an event are so large that it makes sense to take the risk seriously," Holdren told lawmakers.
NASA scientists have made headway in detecting 95 percent of the giant objects that pass near Earth’s orbit and that could destroy parts of Earth if they enter the atmosphere. However, when it comes to the smaller objects, Earth appears more vulnerable as the scientists could identify only 30 percent of the 4,700 or so 330-footers (100 meters) that come uncomfortably close in their orbits, a NBC News report on Science stated.
The attempts to track the objects that fly dangerously close to Earth have intensified in the recent years. NASA and several federal and private space agencies are also working towards developing methods to avoid a possible collision.
Since Earth cannot deviate from its trajectory or protect itself, space scientists are mulling over various methods to deviate the asteroids that are destined to collide with Earth. The options include using nuclear bombs to deflect the asteroid’s course to destroying them through atomic explosion. Some scientists claim spray painting the asteroid to nudge it off the trajectory.
However, the scientists say that to exercise any such options an early and accurate detection — before several years or decades before it is scheduled to touch Earth’s atmosphere — is necessary.
At present, the scientists scan the skies with Earth-orbiting telescopes to detect the space rocks, but cosmic rocks like the Russian meteor — which came hidden in Sun’s glare — cannot be detected with these telescopes.
Space experts say that launching of space-based telescopes helps in better detection of such meteors and asteroids as Sun’s glare will not blind them in space.