Making the point, on May 25 double asteroid 1999 KW4 flashed by Earth at a distance of a little over 3 million miles (5 million kilometers). Classified as a potentially hazardous pair, 1999 KW4 is flittering through space on a path that may smack Earth, but not for at least a thousand years. The larger of the two space rocks is around three-quarters of a mile (1.2 kilometers) in average diameter.

It is estimated that there is a near miss of Earth's orbit by an object every half-hour.

We need to improve our response time... Right now, there is no quick response capability. If we had an emergency today, it would take at least two years to put a system together. We'd like to see that reduced to a few weeks.
     -- Andy Smith of the International Planetary Protection Alliance

Not only can faster, better, cheaper microsatellites help snoop for asteroids, they are ideal for up-close inspection, as well as for pushing space rocks out of harm's way.

There's no good news in the event that Earth gets a calling card from the cosmos anytime soon.

Mark Boslough, principal member of the technical staff in the computational physics department of Sandia National Laboratories in Albuquerque, said supercomputer simulations paint a less-than-rosy picture.

"Once you get into a kilometer-size range of impactor, it is going to be bad news," Boslough said. "Those happen, on average, once every 300,000 years."

Computer work at Sandia demonstrates how impacts can induce climate change. At hypervelocity speeds, an object basically changes the chemistry of the atmosphere. "A lot of greenhouse gases are created, adding to dust and soot from global firestorms. You end up having something equivalent of a nuclear winter," a sun-blocking event that, over time, runs from very cold to high heating of Earth's surface, Boslough said.

Boslough said that computer modeling of impactors show how a ring of debris would be formed around Earth. This band of particles would persist, blocking sunlight and also playing havoc with global temperatures.

If that's not bad enough, debris shot high above Earth would surely impact low-orbiting satellites, Boslough said.

Plunking down in ocean waters, an asteroid measuring several miles (kilometers) across would churn up frightening tsunami conditions, said Jack Hills, a researcher at neighboring Los Alamos National Laboratory.

For example, given an impact far out in the Pacific Ocean, those along the California coastline might have several hours of time for fleeing to higher ground. But on the Atlantic coast, with high mountains far from shore, the situation is perilous.

"Long Island would be totally hosed," Hills said. "I'm not sure people should have been allowed to build there, not just because of any asteroid impact threat but even from storm surges. If something occurred today, it would cause over $100 billion in damage on Long Island," he said.

Be it a city buster, tsunami killer, civilization destroyer or mass-extinction impactor, challenging work is ahead to fend off future terror falling from space.

"We need to improve our response time," said Smith of the International Planetary Protection Alliance. "Right now, there is no quick response capability. If we had an emergency today, it would take at least two years to put a system together. We'd like to see that reduced to a few weeks," he said.

It is time to come to grips with the issue of planetary defense, said Apollo 17 Moonwalker, Harrison "Jack" Schmitt.

"How do you deal with a discovery of an Earth-crossing asteroid that actually is Earth-crossing? It's one thing to chart asteroids and analyze their trajectories, Schmitt said. "We have the technology base. We just haven't implemented it from an engineering point of view to do something about it," he said.

"This is the first time a species can do something about their supposedly inevitable extinction. It's a great time to be living," Schmitt said.