Asteroids - those millions of chunks of space rock, large and small, that drift and spin across our solar system - hold promise for space explorers even as they pose a threat to us on Earth.
When NASA Administrator Charles Bolden discussed the U.S. space agency's proposed 2014 budget with lawmakers in late April, he highlighted a new mission
- a plan to capture an asteroid in deep space and bring it to the vicinity of the moon, where astronauts could later explore it.
"We are developing a process or technology that will come forward in the asteroid retrieval mission that will demonstrate that humans can, in fact, alter the path of an asteroid that's headed toward Earth," he said.
A key part of the planned mission, Bolden underscored, is to show that an asteroid's path can be diverted.
Watch Asteroid Initiative Animation (Courtesy: NASA)
Earlier this year, a small meteor unexpectedly exploded over Chelyabinsk, Russia, and produced a shockwave that shattered thousands of windows and injured more than 1,000 people. The same day, a well-tracked, 45-meter-wide asteroid called 2012 DA14 whizzed safely past Earth, closer than our geosynchronous satellites. It was a record close approach for something that size.
Experts say asteroids larger than 100 meters across strike the Earth's surface, on average, about once every 10,000 years, and there are no records of an asteroid killing anyone in modern history.
John Holdren, the U.S. president's assistant for science and technology, discussed asteroid threats at a hearing on Capitol Hill in March. He told lawmakers that given the rarity of large asteroid impacts, the potential loss of human life from such an event works out to fewer than 100 people per year, which he compared to 5 million deaths each year from tobacco.
"It doesn't look like a very big threat," Holdren said. "But, of course, that is not really a meaningful way to present a risk of this character, where you're talking about a low probability of a very big disaster, and in those sorts of situations, we tend to invest in insurance to reduce the likelihood of a disaster we would regard as intolerable."
Insurance, of course, was not an option for dinosaurs, which are believed to have been killed off 65 million years ago after a 10-kilometer-wide asteroid crashed into the Earth.
Holdren says an asteroid even a fraction of that size could undo life as we know it. "A one-kilometer asteroid would be carrying energy in the range of tens of millions of megatons. That is as much or more energy as was in the combined arsenals of the United States and the Soviet Union at the height of the Cold War," he said. "An asteroid of that size, a kilometer or bigger, could plausibly end civilization."
NASA estimates it has catalogued 95 percent of near-Earth asteroids that are wider than one kilometer. It says it has found nothing this size that poses a threat to our planet in the foreseeable future.
The space agency is now working to detect and track much smaller near-Earth objects, ones that are 140 meters in diameter or larger. The goal is to identify 90 percent of those by 2020.
That's where Lindley Johnson comes in. He is the program executive for the Near-Earth Objects Program at NASA headquarters in Washington. His office coordinates NASA-sponsored efforts to detect and track potentially hazardous asteroids, as well as comets.
"The first and most important thing, of course, is having the capability to find them early," Johnson explained. "You can't do anything about them unless you know that there is one out there that is a threat. So, that's our primary emphasis - finding them. If we do that job well, then the incidence of us actually being impacted are pretty rare."
Johnson was among hundreds of scientists who attended a United Nations conference on outer space in Vienna earlier this year. His working group recommended creating an international asteroid-warning network and a forum that brings various space agencies together to discuss collaborative approaches to counter dangerous asteroids.
Johnson said they also recommended bolstering disaster response, so national and international agencies could warn people about a potential strike, just as they do about hurricanes or tsunamis. Part of the reason people were injured in Chelyabinsk, he said, is that they did not know what to expect.
"They didn't realize that with a meteor coming in like that, that there would be such a shockwave that windows would be broken out, so they saw the bright flash and ran to the window and were looking at the contrail when the shockwave hit," he said.
As of late April, nearly 10,000 near-Earth objects had been discovered, with about 1,400 of them classified as potentially hazardous.
Funding for NASA's Near-Earth Objects Program is about $20 million per year, reflecting a five-fold increase during President Barack Obama's administration.