March 13, 1998 in Nation/World

In The Year 2028, Earth Will Still Survive New Evidence Shows Asteroid Will Not Be A Smash Hit

Alexandra Witze Dallas Morning News
 

Cancel the asteroid insurance.

The space rock that looked as if it might smash into Earth in 30 years will instead miss by a safe 600,000 miles, astronomers said Thursday.

Two pictures of the asteroid, found Thursday in a photographic archive from 1990, allowed scientists to predict its orbit more precisely, leaving Earthlings plenty of breathing room on Oct. 26, 2028.

That’s the date astronomers expected asteroid 1997 XF11 to swing a mere 26,000 miles from Earth’s surface, according to preliminary calculations released two days ago.

But, according to the new prediction, Earth is safe. “This is a non-event,” said Don Yeomans of the Jet Propulsion Laboratory in Pasadena, Calif.

Yeomans and colleagues have recalculated the mile-wide asteroid’s trajectory based on two pictures found by JPL scientist Eleanor Helin in her archive of asteroid photos. The pictures show where the asteroid was situated eight years ago - long before it was spotted in December and given the designation of a new asteroid.

Finding the 1990 photos gives astronomers better information on the asteroid’s positions eight years apart, rather than just the three-month period since its “discovery” in December. That new data allowed Yeomans and other astronomers to recalculate the orbit much more accurately than they could have just two days ago.

“XF11 is certainly not going to hit us in 2028,” said Gareth Williams, an astronomer at the International Astronomical Union’s Central Bureau for Astronomical Telegrams, which issued the initial alert.

That alert was an e-mail announcement like others routinely sent out when an unfamiliar or unusual object is discovered and needs more observation. The alerts serve as a warning for other scientists to get out their telescopes - or their old photographic plates - and start searching for the object.

Scientists knew future or past observations would help them refine the orbit predictions, but it’s not often such additional information is so quickly found in archival photos.

By calculating the object’s orbit back in time, Helin recognized the asteroid in her photographs was the right object. But its position in the newly found images was slightly different - enough to alter the forecast of where it would be in 30 years.

After hearing about Helin’s two photos, the International Astronomical Union group also re-calculated the asteroid’s orbit late Thursday afternoon. It also found that the asteroid would miss Earth by 600,000 miles, said Williams.

The International Astronomical Union, based in Cambridge, Mass., serves as a clearinghouse for astronomical discoveries.

Even before the discovery of Helin’s old photos, scientists hadn’t been in complete agreement about whether 1997 XF11 truly posed a threat to Earth.

Calculations by the International Astronomical Union, Yeomans and several other scientists showed Wednesday the asteroid would pass within 30,000 miles of Earth’s center, or 26,000 miles above Earth’s surface. That would have made it the closest asteroid ever known to have passed Earth.

But the Cambridge group said its calculations showed Earth lay within the margin of error of that orbit.

But Yeomans said the 30,000-mile margin of error encompassed a region shaped more like a long, skinny cigar than like a circle - and that Earth didn’t lie within that cigar. Even the initial calculations shouldn’t have indicated Earth may have been within the error zone, he said.

Although scientists now have a new number for the asteroid’s closest approach, they cautioned it too could still change after more observations.

“We say 600,000 miles, but that’s not set in stone either,” said Dan Green of the International Astronomical Union.

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