WASHINGTON (Reuters) - An asteroid that is headed toward Earth is not going to hit us after all, NASA said Thursday.

It would miss the planet by 600,000 miles, NASA researchers said.

The International Astronomical Union (IAU), which keeps track of such objects, said late Wednesday that an asteroid would pass very close to the Earth in the year 2028 and might conceivably hit it.

The IAU appealed for astronomers to have a look at the asteroid, dubbed 1997 XF11, and see if they could get more information about its size and orbit.

NASA spokesman Don Savage said a team at the space agency's Jet Propulsion Laboratory (JPL) had done just that.

"The latest numbers are in -- 600,000 miles from the Earth is the latest determination of the orbit," Savage said.

That is far outside the orbit of the moon, which is about 240,000 miles from the Earth.

"It's all in a day's work," said Don Yeomans, a senior scientist at NASA's JPL, who helped make the calculation that saved the Earth from possible destruction.

He and colleague Paul Chodas took a second look at the data on 1997 XF11, which was first spotted last December. Even at that time, they predicted the probability of a collision would be zero.

But to be sure, they went through old photographs that astronomers had taken of the sky, some of which showed the asteroid, which no one noticed at the time.

"We re-did the analysis and the close approach distance moved way out 600,000 miles, which is 2-1/2 times the lunar orbit," Yeomans said in a telephone interview.

"Nobody can argue with it. This sort of puts the nail in the coffin."

Chodas said just to be sure, the JPL team was not saying XF11 would definitely not collide with the Earth.

"The probability of impact, we don't want to say that it's absolutely zero. I think we are going to rework our computation of the number," Chodas said.

"But it is very, very tiny and the impact is extremely unlikely."

Chodas said the asteroid was in an elliptical orbit around the sun just slightly, about four degrees, at an angle to Earth's. It takes about 21 months to complete an orbit.

That brings it into Earth's orbit regularly.

"We are performing a dance," Chodas said."The Earth's going around the sun and this thing is going around in its orbit."

Asteroids have hit the Earth in the past. A 5-mile wide asteroid that hit what is now the Yucatan Peninsula in Mexico 65 million years ago is believed to have caused worldwide disturbances that sent the dinosaurs into extinction.

Either a small asteroid or a large meteorite caused an explosion in 1908 near Tunguska, Siberia. Whatever it was vaporized before it hit the ground but it flattened hundreds of square miles of trees.

Experts say a large bomb could probably be used to deflect any asteroid heading toward Earth.

"Yeah, we could do it," Yeomans said."We would send out a spacecraft with a nuclear weapon probably...we would set it off one asteroid radius from the surface. It would slow the asteroid just enough so that in 30 years it would miss the Earth."

Yeomans did not understand why the IAU announced the possible near-miss Wednesday."Why did they put out a press release before putting out the data and consulting with our colleagues? I don't know," he said.

A group of experts would meet in Houston next week to discuss such issues and to talk about better ways to announce the discovery of near-Earth objects. "We can't go through this again," Yeomans said.