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Friday, March 20, 1998

Is the sky falling? Let's check the math first

By PAULINE ARRILLAGA / Associated Press Writer

HOUSTON (AP) -- A week after coming off like Chicken Little with a Ph.D., some astronomers have resolved to make sure they're right the next time they announce the sky might be falling.

At a meeting this week in Houston, 15 astronomers from around the country agreed to form a committee that will use its combined expertise to calculate the risks to Earth when an asteroid looks like a threat.

"This group would be charged with assessing the threat and reaching a consensus and a clearer plan for defining the nature of the threat," said Donald Yeomans, a scientist with NASA's Jet Propulsion Laboratory.

"We don't cry wolf. If it's a real threat, the announcement will be made and steps will be taken to mitigate the threat."

Last week, it appeared a group of astronomers, the International Astronomical Union, had cried wolf when they issued an alert saying an asteroid would pass within 30,000 miles of Earth -- and might even collide with it -- on Thursday, Oct. 26, 2028, around 1:30 p.m. EST.

The next day, Yeomans -- citing new data -- said the asteroid would pass no closer than 600,000 miles and had no chance whatsoever of hitting the planet.

All parties seem to agree the gaffe could have been avoided had the International Astronomical Union and NASA communicated earlier.

"It's in our best interest to try to get harmonious again," said Brian Marsden, the distinguished Harvard astronomer who made the IAU calculations.

Mardsen and Yeomans were among the astronomers who met Tuesday at Houston's Lunar and Planetary Institute and decided to form the peer review committee.

When an astronomer discovers that an asteroid could threaten the Earth, the committee will review the data and do its own calculations to determine how serious the threat is.

"Within a matter of a day or two, the situation will become far more clear and it will either become a nonevent or some appropriate announcement will be made -- but not until this committee's had a chance to chew on it for a bit," Yeomans said.

The committee members have not yet been selected, but they are likely to include both Marsden and Yeomans.

Marsden admitted the entire asteroid episode "left a nasty taste in my mouth."

Marsden said he made his calculations based on all the data available at the time. In Marsden's 40 years of tracking asteroids, the space rock was the first with the potential of coming so close to the Earth. He said he decided to make an announcement to try to obtain additional data.

Eleanor Helin of the Jet Propulsion Laboratory immediately called Marsden and said that based upon his data, she had found 1990 telescopic images of the asteroid that could be helpful.

Using those pictures and recent observations, Ms. Helin's group calculated the asteroid's new position and forwarded the information to Marsden and her colleague, Yeomans. Yeomans simply beat Marsden to the punch by releasing the information, she said.

"I'm very disappointed in how this unfolded," Ms. Helin said. "It appears that people are trying to pit (Marsden's group) against NASA and vice versa when, really, we're all friends."

What's been lost in all the sniping, said Ms. Helin, is the fact that 1997 XF 11 is still a potentially dangerous asteroid.

"The public actually thinks that this went from being a serious risk one day to never mind it's no problem the next," she said. "OK, so it's under 600,000 miles now. The point is it's coming close, and it's big."