Okay, so we've spotted a wicked wanderer headed our way. Now what?

There is no "magic bullet' solution of a single purpose mission to counter a threatening NEO, said Thomas Matula, a professor at the University of Houston - Victoria, in Sugar Land, Texas. A multi-mission strategy is more likely to succeed in deflecting or destroying a NEO, he said.

"We have the ability today to build the spacecraft needed for the multi-mission strategy at a cost within funding limits for a NASA Discovery mission. That is a very modest price considering that thousands, or even millions, of people might die in a NEO impact," Matula told SPACE.com.

To date, most researchers assume if a NEO is found to be on a crash course with Earth that a spacecraft can quickly be launched to deflect the object, Matula said. Dealing with a NEO is much more complicated. Numbers of craft would need to be rapidly dispatched, he said.

First, a scout spacecraft would perform the necessary data gathering about the object, even deploy mini-landers on the object to map sub-surface fractures and chemical composition.

Once it has surveyed the NEO, the scout scoots to a safe distance. It then supports a command and control spacecraft. That vehicle guides a transport spacecraft loaded with mini-landers, each toting a nuclear device. A set of those mini-landers are let loose, either plopping onto the surface of the NEO or put on a specific heading to intersect the targeted object.

Detonation of the lander-carried nuclear devices takes place, busting up the NEO or vectoring it on a path that misses Earth. Distant from the explosive action, the scout spacecraft makes a post-strike survey. If the NEO or its remains still prove troublesome, the armada could be repositioned for repeat strikes.

"Our generation is the first one in history to have the technology needed to protect the Earth from NEO impacts. If a NEO does hit the Earth and kills a large number of people, we will have to explain to future generations why we didn't use that technology to protect them," Matula said.

So what happens when the next NEO smacks into Earth? It is not too early to think about emergency preparedness, Smith said.

Effects caused by a NEO colliding with Earth can vary, depending on size of the incoming object. There can be fire, blast effects, tsunamis, and other localized havoc. If big enough, a NEO impact might generate an asteroid winter that could last for months to years. In this instance, sunlight-blocking residue heaved high into the Earth's atmosphere would shut down ecosystems that, in turn, spark crop failure and mass starvation.

Whether small or large, NEOs can yield a nasty knock out punch of one sort or another.

Increased public and governmental awareness about the potential threat from comets and asteroids is a priority. Consciousness raising work about NEOs is underway in many nations, IPPA's Smith said, but much of it done by volunteers and groups operating on very limited budgets.

With the Earth largely covered by oceans, tidal waves sent roaring toward coastlines by an impactor must be considered. Evacuation routes for coastal cities should be well thought-out.

"On the East Coast, there's not much high ground. There are too many people that can't move fast enough. So that's a big problem," said Phil Richter, a structural engineer astute in the effects of natural disasters. "What to do about it is a little bit staggering," he said.

If the really big one augured in, we need ways to feed people under low-light conditions from months to years. Underground shelters need to be improved and fully stocked with survival rations, Smith said.

The horrific events of 9/11 involving New York's Trade Towers demonstrated how difficult the job of rescue can become, said Dan Stormont, a robotics expert from Utah State University in Logan.

"Robots can find victims within disaster areas. It's a hostile environment, like exploring a planet with potential radiation, extreme temperatures, and an atmosphere that can't be breathed," Stormont advised. Stockpiles of tiny robots, more like "insectoids" equipped for search and rescue, can aide in post-NEO impact work, he said.

David Miller, a robotics specialist and engineer at the University of Oklahoma in Norman, said a NEO striking a major U.S. east coast or west coast city would be devastating to American infrastructure. "The United States would be out of the running for months. If we had a sizeable event that hit anywhere causing damage…it's scary to think about," he said.

The aftermath from a grand slam NEO is formidable, taxing resources of food, water, shelter, and the safety of perhaps a million people or more, said Laurance Higgs, managing director of FocusZenith Limited of Nottingham, the United Kingdom.

Higgs questioned whether countries around the world could cope with mass exodus of shocked and stunned people from one nation to another. The economic ramifications are so severe, he urged that an international body should start looking at ways to prevent such damage from ever taking place, he said.