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Asteroid to cross paths with Earth

A newly found asteroid, large enough to wreak worldwide destruction, will cross Earth's path in 2019, and although the chance of a collision is slim, astronomers cannot yet rule it out.

If the asteroid, named 2002 NT7, were to hit, it would be on Feb. 1, 2019. The odds of that happening are less than 1-in-200,000, NASA's Jet Propulsion Laboratory calculated Wednesday.

That is roughly the same chance that an unknown, as yet unseen meteor will hit Earth between now and then. Scientists expect the 1-in-200,000 odds to grow longer as they learn more about the asteroid's orbit.

On the zero to 10 Torino scale describing asteroid hazards, 2002 NT7 currently ranks a "1," meriting careful monitoring but with the chance of impact judged extremely unlikely. A "0" means no danger; a "10" means certain impact with worldwide devastation.

In earlier asteroid scares, astronomers quickly ruled out any chance of impact, or the potential impact remained so far in the future that it was impossible to accurately judge the risk.

Astronomers first spotted 2002 NT7 on July 9. With two weeks of observations, they have mapped out its orbit fairly precisely: It circles around the sun once every 837 days at a steep tilt of 42 degrees compared to the general orbits of the planets.

But astronomers have not yet pinned down the asteroid's current location, which means their predictions of where it will be on Feb. 1, 2019, may be off by tens of millions of miles.

"It's the old train on the track problem," said Donald K. Yeomans of the Jet Propulsion Laboratory. "You don't know when the train is going to arrive at the crossing point."

If NT7, which is 1\ miles wide, does strike Earth at 60,000 mph, the impact would gouge a crater tens of miles wide, wiping out the better part of a continent and possibly causing long-lasting climate change.

It would enter the atmosphere at nearly 64,000 mph and strike with the explosive energy of 1.2-million megatons of TNT, according to JPL estimates.

On average, an asteroid of NT7's size hits Earth once every few million years. The meteor that killed off the dinosaurs 65-million years ago was 6 to 9 miles wide.

After 2019, NT7 will have three more close passes by Earth, in 2044, 2060 and 2078. Yeomans said that with a few more weeks of observations, astronomers will probably be able to rule out any chance of impact for all of them.