What are the odds an asteroid or meteoroid will hit the Earth again? Pretty good, according to some scientists.
There are millions of these "rocks" out there, and about 200,000 to 400,000 of them get close enough to be classified as celestial objects that could come within range of our home planet.
But it only takes one, as anyone who has studied the dinosaurs will tell you. Many scientists believe an asteroid impact led to the extinction of the dinosaurs 65 million years ago.
Apollo 9 astronaut Russell Schweickart believes it is simply a matter of time before another asteroid targets Earth.
"It could be 20 years, or a hundred years, or a thousand years," he said.
Schweickart is one of the founders of the B612 Foundation, which studies how to alter the orbit of an asteroid to prevent it from hitting Earth. "It's a very infrequent occurrence -- an asteroid impacting the Earth -- but when it happens, it will be devastating."
Schweickart says he's frustrated because he believes this project should be led by an international organization. He contends there is no way to predict when or where an asteroid will hit the Earth, so no single government should be held responsible for asteroid avoidance.
He wants to see the United Nations set up an agency mandated to prevent an asteroid from colliding with the Earth and has planned a series of meetings around the world to develop a comprehensive plan. Schweickart anticipates a project that would cost several hundred million dollars, a burden for any single country, but something much more practical as a combined effort.
How would you keep an asteroid form hitting the Earth? Schweickart outlined a three-step program.
Early Warning. You need to know it's coming by searching for it. NASA currently has a budget of $4.1 million to look for asteroids.
Take Action. Develop the ability to deflect an asteroid. Some technology is available now, but propulsion that doesn't exist yet will be required -- nuclear reactors that could power ion-propulsion systems for interplanetary spacecraft.
Make a Decision. Some agency has to decide to do this and fund it. This isn't about ducking a bullet going past your head; this is about seeing what is coming your way decades ahead and believing in the laws of gravity.
Edward T. Lu is a NASA astronaut who has developed a plan of action for deflecting an asteroid. He and fellow astronaut Stan Love have come up with the concept of a space tug. A space tug is a rocket that would launch to the same orbit as an asteroid threatening to hit the Earth and alter the asteroid's orbit by pushing in the direction of its orbital motion.
Lu told ABC News, "You don't have to change much -- one hundred thousandth of a mile an hour is enough, 10 years ahead of time, to cause an asteroid to miss the rendezvous with Earth."
NASA is taking some steps to learn more about asteroids. Chris McKay is a planetary scientist with the Ames Research Center as well as the deputy lead scientist for the Constellation Program -- the project to go back to the moon and on to Mars. Orion is the vehicle that will carry the astronauts, launched with an Ares rocket. McKay is exploring ways to use Orion for other missions, like sending a crew to land on an asteroid.
"It is exciting to think about rendezvousing with an asteroid and bringing back samples," McKay said. "What we could learn about the origins of the Earth is mind-boggling."