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NASA: Asteroid to miss Earth by a wide margin


'Probability of an impact is zero'

In this story: March 12, 1998
Web posted at: 10:12 p.m. EST (0312 GMT)

WASHINGTON (CNN) -- Relax. That mile-wide asteroid that astronomers thought might be headed for a near-miss -- or a collision -- with Earth isn't going to come that close after all.

NASA scientists said Thursday there is no chance -- "zero" in the words of one astronomer -- that the asteroid known as 1997 XF11 will come any closer than 600,000 miles from Earth.

"We are saying now that the probability of an impact is zero," said Donald K. Yeomans of NASA's Jet Propulsion Laboratory.

The International Astronomical Union reported Wednesday that it appeared the asteroid would pass within just 30,000 miles of Earth and might even hit the planet in October 2028. The IAU appealed to other astronomers to study the asteroid and see if they could get more information about its size and orbit.

Yeomans said he and fellow astronomer Paul W. Chodas dug out some 1990 pictures taken by the Palomar Observatory telescope and found that the photos contained images of asteroid 1997 XF11, which was then just an unidentified point of light.

Using the 1990 pictures, along with recent observations of the streaking space rock, Yeomans and Chodas recalculated the orbital path of the asteroid and found that it would miss the Earth by 600,000 miles in its closest approach in October 2028.

JPL scientists had '8 years of data'

Carl Pilcher, NASA
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"How did NASA arrive at this new calculation?"
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    CNN's Judy Woodruff talks to NASA's Carl Pilcher about the asteroid

    The astronomers who made the original prediction could not immediately be reached for comment. But NASA spokesman Carl Pilcher defended them, in a sense, when he told CNN Thursday that those scientists used limited data.

    "They had only 90 days of data" after spotting the asteroid in December, Pilcher said. The scientists at JPL, however, had the benefit of that data "plus data from 1990. So, in essence, (Yeomans and Chodas) had eight years of data."

    With that additional data, Yeomans and Chodas projected a different trajectory for the asteroid that will carry it outside the orbit of the moon, posing "no threat to the Earth whatsoever."

    Brian G. Marsden of the IAU had issued the initial notice about the asteroid Wednesday to other astronomers. He said then that "the chance of an actual collision is small, but one is not entirely out of the question."

    "An object this size only hits Earth once every few hundred thousand years," Pilcher said Thursday, "so we wouldn't have expected this one to be on a collision course" with Earth.

    Pilcher said that while big asteroids like 1997 XF11 get all the attention, "smaller ones hit quite often."

    He mentioned one that struck Siberia in 1908. Although it vaporized before striking the ground, it flattened hundreds of square miles of trees.

    Such asteroids, he said, "happen once a century."

    'Something we should be conscious of'

    Pilcher said a 10-mile-wide asteroid that landed on what is now the Yucatan Peninsula in Mexico 65 million years ago caused the extinction of the dinosaurs.

    "They're something we should be conscious of and give some thought to," he said, "but not something that anybody has to be worried about for their safety next week."

    Last October, U.S. President Bill Clinton used his line-item veto to cut a $30 million "Clementine" Asteroid Intercept Technology Demonstrator from the federal budget. The project involved tracking three asteroids this year and next and sending spacecraft to intercept them.

    On Thursday Wisconsin Rep. James Sensenbrenner, who chairs the House Committee on Science, asked Clinton to reinstate the program.

    "This project would have been a low-cost proof of concept for any future attempt to protect our planet from an asteroid collision," said Sensenbrenner.

    Duncan Steel, a former astronomer at Australia's University of Adelaide, has been warning of the asteroid danger for years. He helped set up the Rome-based Spaceguard Foundation to heighten awareness of the asteroid danger and wants to set up a global chain of telescopes to watch for asteroids.

    Reuters contributed to this report.


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