But some say a serious asteroid strike is just a matter of time, and we should be ready.
For evidence of what might come, see the 1908 "Tunguska event" in Siberia, said Ed Lu, a former shuttle and International Space Station astronaut who heads the nonprofit B612 Foundation (the name references the asteroid home from "The Little Prince.")
A relatively small comet or asteroid that exploded before hitting the ground wiped out that unpopulated area of Siberia in 1908 with a force 1,000 times greater than the bomb dropped on Hiroshima, leveling forests, photographs later showed.
"These hit the Earth about every 100 to 200 years," Lu said this fall. "So flip a coin. That's the odds that somewhere on Earth during your lifetime it's going to happen again. Random spot. Most of the world is unpopulated. But wouldn't it be a shame if it was a populated area?"
No such strike is imminent, but the Mountain View, Calif.-based foundation has embarked on a privately funded mission, called Sentinel, that it believes could save humanity from going the way of the dinosaurs.
The mission plans to catalog 90 percent of the near-Earth asteroids at least 460 feet wide that could cause devastating damage, plus many more as small as 100 feet, to provide the notice needed to deflect any threats.
Deflecting an asteroid is relatively easy with enough warning, because its velocity need only be tweaked very slightly to turn a hit into a miss, Lu said. A spacecraft could impact an asteroid or act as a "gravity tractor" to pull that off.
The problem, Lu said, is that we know the locations of only a fraction of the asteroids that whiz through Earth's vicinity.
"We're driving around the solar system with our eyes closed, essentially, and that seems kind of crazy, right?" he said. "Because these things do hit the Earth."
To open Earth's eyes, the B612 Foundation has partnered with Boulder, Colo.-based Ball Aerospace to design and build a roughly $500 million infrared space telescope able to spot hundreds of thousands of asteroids.
The proposed spacecraft, which has passed a preliminary technical review, is the size of a FedEx van . The foundation hopes to launch it on a SpaceX rocket by 2018, possibly from Cape Canaveral.
Sentinel would launch into a Venus-like orbit around the sun, repeatedly taking pictures as it scans the sky.
"As the sun shines on these asteroids, they warm up and they glow, and we're putting the night vision goggles together in Sentinel that can see that object," said John Troeltzsch, the project manager at Ball, in a recent interview.
Comparing images of the same patches of sky will reveal objects that have moved - asteroids. Further analysis will determine their orbits or identify objects for follow-up.
Lu said Sentinel would discover 10,000 asteroids a month - about as many as have been cataloged to date. The mission will last at least five-and-a-half years.
Aside from its scientific goals, Sentinel is notable because it seeks to raise a huge sum to fly what Troeltzsch called the "first privately funded deep space mission."
The foundation reasoned that the cost is similar to what some organizations raise to build a new wing on an art museum. So why not pursue such an important mission on their own if cash-strapped governments wouldn't?
"It's almost a litmus test for a civilization to figure out whether or not they can figure out how to do something about (an asteroid) before they get smacked, right?" Troeltzsch said. "And we're at a point in time now where we can raise the money, we have the technology to do it, we have the concepts, the data analysis. It all comes together. We could change the evolution of the Earth."
On its website, the foundation solicits donations as small as $25, asking, "Do you want to help map the great unknown and protect life on Earth?"
Said Lu: "We are going to find and track threatening asteroids before they find us."
(Copyright © 2012 USA TODAY)