Trying to stop the big smash

The premise of a giant asteroid hitting the earth and ending civilization has become an increasingly popular threat in movies and video games. But until now, having Ben Affleck and Bruce Willis land on a space rock and nuke it to smithereens has been as close to an asteroid defense plan as NASA has gotten.

Astronomy professor Michael A'Hearn is working to change that.

"There is no plan," he explained.

Besides spearheading a NASA effort to locate 90 percent of near-Earth objects — comets, which emit gas and rocky material, and asteroids — that orbit within a 140-kilometer (about 87 miles) diameter of the earth, A'Hearn was also the lead author of a report released last month examining scientific options that could be used to prevent an asteroid or comet strike from dealing major damage to earth.

Statistically, a small asteroid of about 25 meters in diameter should hit the earth every 250 years, A'Hearn said.

"The really small ones aren't going to do any damage, so we can ignore them," A'Hearn said. "If it's big enough that it would cause damage, we can predict where they will hit, at least with the same accuracy and time frame that we can predict hurricanes and evacuate the area, as long as we're confident that it's a reasonably small one."

But a bigger one — like the one Willis and Affleck battled in Armageddon — would be a bigger problem. And methods to combat it enter the world of science fiction.

"If we get a little bit bigger, then we have to change its course," A'Hearn said. "To do that, we would send out a gravity tractor, which is a small spacecraft, which is still large in comparison to the NEO; the spacecraft slowly tugs the NEO. This technique can be very precise, but you need a really large advanced warning, and it doesn't work if the NEO is very big."

Other possibilities include impacting the asteroids at high speeds or attacking it with a nuclear weapon, although more research is necessary to determine if either method is feasible.

And before humanity can even think about stopping a giant NEO from striking earth, we need to locate them. Congress gave NASA a mandate to locate 90 percent of the most threatening NEOs by 2020, but until President Barack Obama's recently released 2011 budget proposal, neither Congress nor the executive branch has tried to fund the mandate over the past five years. And even though NASA is charged with finding the objects, no agency is responsible for preventing them from doing major damage.

"NASA currently has the responsibility of finding them, but not for doing anything about them. It's not in NASA's mandate at all — it's not in anybody's mandate," A'Hearn said. "Certainly within the next year, there will be a lead agency within the U.S. government designated. It is clear there will be an increase in the budget that goes to some aspect of NEOs. I'm not sure if the president's budget has enough to do it right, but it's a step in the right direction."

A'Hearn has been studying comets and asteroids for most of his career — usually as part of an effort to understand how the solar system came to be. He's glad policymakers are paying increased attention to the objects, but he insists there is still more work to be done.

"We still don't know the smallest object that would cause significant damage on the ground," A'Hearn said. "We also need to continue studying the physics of atmospheric entry."

hemmati@umdbk.com