Cheng said that on any registry of rogue asteroids considered the most dangerous, Eros should be on that list. "Not for the immediate future, but a hundred million years from now," he said.

"Eros is one of the guys that could have our name on it."

It turns out that Eros traces a chaotic orbit in its space trek around the sun. While the more than 20-mile- (33-kilometer-) long asteroid does not swing out that far into deep space, the path it does pursue is influenced by giant Jupiter, the largest planet in the solar system. And those gravitational twists and tugs on Eros make plotting its exact whereabouts difficult.

"Eros is one of the most likely asteroids that will hit the Earth, and that's only recently been discovered," Cheng said.

Predicting certain asteroids with Earth orbit-crossing trajectories that can be diverted by gravity fields of other planets is a real issue, said Roald Sagdeev, professor at the University of Maryland in College Park. He is the former director of the Institute for Space Research, part of the Russian Academy of Sciences in Moscow.

"New technologies will be needed to deflect asteroids from our planet," Sagdeev told SPACE.com.

"The earlier you discover that an asteroid is dangerous, the smaller the force needed to change its trajectory," he said. "If we learn that an asteroid is moving and in 10 years would hit us, it would be too late. The only resource would be to bring a hydrogen warhead and explode it there. I think this project, and these type of studies, would help us to understand what can be done with asteroids."

In the Earth-defense scheme of things, the biggest threat is not only which asteroid's orbit will intersect with our planet, but how fast that object is coming, said Lucy-Ann McFadden a NEAR science team member from the University of Maryland.

McFadden said NEAR could give Earthlings a heads-up on how to battle an incoming threat from afar. "We've never orbited an asteroid before," she said. "We are getting valuable experience in navigating NEAR. If we do have planetary defense, we need to learn how to sidle up to an asteroid, give it a nudge and change its orbit so it'll miss us."

But Eros is a whopper when contrasted to other cosmic flotsam. A much smaller fraction of objects less than a mile in diameter are also part of the heavens above. They are much tougher to detect, said Jack Hills, a scientist with Los Alamos National Laboratory in New Mexico. His research suggests that these "swords of Damocles" can strike Earth at any time, with almost no warning.

Objects just a few hundred feet across, for example, would create blast waves that could reduce to rubble the largest cities on Earth if they impacted near them.

A "snag and tag" philosophy is advocated by physicist Edward Tagliaferri, president of ET Space Systems in Camarillo, California. He argues that precise tracking of Earth intimidating asteroids is a must. Changes in the trajectories of objects that cross Earth's orbit are not fully understood. Therefore, an asteroid once viewed as non-threatening to Earth may later be found to be dead-on target. For those pesky planetoids rated as worrisome, they would be outfitted with a beacon.

"There really are threatening objects out there. We've been ignoring that factand to my mind, that's not playing it smart," Tagliaferri said.

Meanwhile, NEAR scientists are gathering here as images of asteroid Eros stream in from space. On Valentine's Day, NEAR is set to begin a year-long mission orbiting this rock of ages.