JPL WATCHING ASTEROID NEAR EARTH'S ORBIT.

Byline: Eric Wahlgren Daily News Staff Writer

Scientists have discovered an asteroid as wide as three football fields that they said Friday belongs to a class more likely to hit Earth than other known galactic rocks.

A computer-driven camera on Maui, Hawaii, operated remotely by National Aeronautics and Space Administration's Jet Propulsion Laboratory in Pasadena, first spotted the asteroid Jan. 10, sending astronomers scrambling to plot its trajectory.

So far they are not sure when it will slam into Earth, if ever.

``But it is moving very closely around the Earth as it orbits the sun,'' said Eleanor Helin, a JPL planetary astronomer. ``The question is, how much closer is it going to get? These are the objects that we do not like to see come this close.''

Particularly, she said, because this rock, dubbed 1997 AC11, is hurtling close to 50,000 mph and is believed to measure up to 1,000 feet in diameter.

It most recently crossed the Earth's orbit Jan. 22 and 23, missing the green planet by 10 million miles, which astronomers say is a pretty close call. The asteroid will continue to slice through Earth's orbit every 9-1/2 months or so as it courses around the sun.

Helin said the hulking piece of cosmic debris is one of 24 so-called ``Aten'' asteroids, putting it in a small class of asteroids that frequently cross the Earth's orbit. Aten is the name for the sun god in Egyptian mythology.

Scientists estimate the odds of any large asteroid slamming into the Earth are extremely low, amounting to one collision every 300,000 years. So far, they have documented about 415 near-Earth asteroids, those that intersect with the Earth's orbit.

This newest asteroid is up to 50 percent more likely to hit Earth than other types of asteroids, said Helin, who pioneered the study of Aten asteroids in the 1970s.

And that's not a good thing, she said.

The galactic intruder is perhaps 10 times larger than the asteroid that struck Arizona more than 25,000 years ago and formed the famed 4,000-foot-wide, 700-foot-deep Meteor Crater.

``Given the size of (1997 AC11), there would certainly be a large area of destruction,'' Helin said. ``If something like this falls into the ocean relatively close to the coastline, it produces very dangerous tsunamis with waves several hundred feet high.''

Smaller rocks fall to Earth more often, Helin said, citing an incident in Peekskill, N.Y., in 1995 when a 27-pound meteorite hit a woman's car that was parked in her driveway.

``She rushed out only to see the rear end of her car was crushed and there was this big rock still warm to the touch,'' Helin said. ``These things happen.''

The arrival of 1997 AC11 helps further blur the line between TV and reality; a four-hour television miniseries called ``Asteroid'' is set to air in February on NBC.

In the two-night action-thriller, a Colorado astronomer discovers asteroids that are on a collision course with the Earth, including one that later takes out part of Kansas City.

The producers call ``Asteroid'' `` `science faction' and not science fiction,'' said NBC spokeswoman Cathryn Boxberger. ``They were always aware that an asteroid hitting the Earth is a possibility.''

Helin prefers to play down the threat of asteroids hitting the Earth. After all, there would be little that people could do to avoid disaster, she said.

Even if astronomers knew about an asteroid's impending impact months in advance, Helin said, it would be hard to evacuate cities or predict where it would land.

Some scientists have suggested using an airborne laser to cut up asteroids, while others have talked about obliterating the mass altogether with a nuclear missile.

JPL snapped pictures of the asteroid using its Near-Earth Asteroid Tracking system at Mount Haleakala in Maui, which beams the information to Pasadena.

The telescope, on loan from the Air Force, is designed to spot objects of military significance.

Along with the asteroid, scientists Jan. 10 also identified a new comet named 1997 A1. It will come closest to Earth on Thursday, when it passes at a distance of about 370 million miles.

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