'Deep Impact' in Real Life: Scientists Track Asteroid Threats

Giant asteroids smashing into Earth and other planets isn't just the stuff of sci-fi movies like Deep Impact and Armageddon -- it's a reality that researchers at the Near Earth Object (NEO) Program (http://neo.jpl.nasa.gov/) of NASA's Jet Propulsion Laboratory take seriously every day.

In fact, scientists at the program will be watching the skies with great interest next month, as they track a newly discovered asteroid that could be headed straight for an impact with Mars.

First observed on Nov. 20, the 160-foot-wide asteroid known as 2007 WD5 currently has a one-in-75 chance of striking Mars. The impact, if it occurs, would take place on Jan. 30 around 5:55 a.m. Eastern Standard Time.

While the odds of 2007 WD5 slamming into Mars aren't great, those numbers could change before the predicted impact date. The asteroid is in an area of the sky that makes it hard to observe right now, but it should become visible to astronomers again early in January. Scientists will then be able to take new measurements to help refine their orbit models. When that happens, they'll have a better idea of whether to expect a Mars-shattering crash at the end of the month.

The asteroid came as close as 5 million miles from Earth on Nov. 1. If it misses Mars, it could eventually pass by Earth again -- maybe in a few years, maybe in decades -- but researchers don't believe the current path makes it a hazard to our own planet.

Near Earth Objects (NEOs) have struck Earth many times throughout the course of its 4.5-billion-year history. Asteroids, in fact, are the leftover bits of the material that came together to form the rocky planets, and they bombarded the Earth and other planets heavily in the early years of the solar system. While those early collisions made our planet inhospitable, later, less frequent impacts might have brought the water and carbon-based materials that enabled early life to develop.

Another impact believed to have occurred 65 million years ago, causing the dinosaurs to die out, probably helped pave the way for a wide variety of mammals and, eventually, humans.

Asteroids don't have to be large to cause Earth-shattering, literally, damage, either. Earlier this month, researchers at Sandia National Laboratories reported that a supercomputer simulation indicated the Tunguska impact nearly a century ago probably involved a body much smaller than previously thought.

The collision on June 30, 1908, devastated huge swaths of forests in the remote Tunguska region of Siberia.

The computer simulation indicates that as an incoming asteroid heats up in Earth's atmosphere, it explodes and sends out a fireball of hot gas that causes greater damage than a simple impact alone would. The researchers' findings suggest the Tunguska explosion was only three to five megatons, not the 10 to 20 megatons once thought.

"That such a small object can do this kind of destruction suggests that smaller asteroids are something to consider," said Mark Boslough, a principal investigator at Sandia. "Their smaller size indicates such collisions are not as improbable as we had believed."

NASA's Near Earth Object Program estimates that asteroids 50 meters (164 feet) strike the Earth on average of every 100 years, causing local disasters or tidal waves. Bodies more than a kilometer (0.62 miles) across can be expected to impact the planet every few hundred thousand years or so. Researchers at the program regularly keep data on objects that have come close to Earth or are expected to. They say any oncoming threat could be deflected away from Earth using nuclear fusion weapons to nudge the body out of its orbit. Blowing up an approaching asteroid isn't a recommended solution, though: all the resulting smaller bits would still be headed for a collision with Earth.