Humans are unprepared to stop such an event, said Joseph Nuth, a researcher with NASA’s Goddard Space Flight Center.
Nuth, who was addressing the annual meeting of American Geophysical Union, said large and potentially dangerous asteroids are rare, but could strike the Earth at any time. "But on the other hand they are the extinction-level events, things like dinosaur killers, they’re 50 to 60 million years apart, essentially. You could say, of course, we’re due, but it’s a random course at that point,” he said.
Nuth noted the Earth had "a close encounter" with a comet in 1996 and then again 2014 when a comet passed "within cosmic spitting distance of Mars." Mankind didn't even know about the 2014 event until 22 months before it hit Mars. But scientists would need a warning time of more than two years to stop a comet from hitting Earth, he said.
"If you look at the schedule for high-reliability spacecraft and launching them, it takes five years to launch a spacecraft. We had 22 months of total warning," he said.
Meanwhile, Cathy Plesko, a scientist at Los Alamos National Laboratory, suggested mankind use a nuclear warhead to deflect an asteroid. "Cannonball technology is actually very good technology, intercepting an object at high speed actually ends up being more effective than high explosives," she said. "We don’t want to be doing our calculations before something is coming. We need to have this work done."
An asteroid that exploded over the Russian city of Chelyabinsk in 2013 injured more than 1,000 people.