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So 2001 PM9 will make 30 passes within the next 80 years? How many passes have we survived already? The recent fervor over asteriod impacts makes me shake my head. Has our danger increased simply because we can now see and identify lots of these rocks?

Offered by Michael.

Asteroid No Threat, Despite Rumors of Earth Impact
Space.COM, August 23, 2001

A newly discovered asteroid whose orbit around the Sun had only been tentatively investigated was rumored last weekend to be on a collision course with Earth. As with similar cases in recent years, further scientific observations showed the asteroid, called 2001 PM9, poses no threat. But before these additional observations could be made, the initial data collected on the space rock was released on a public Web site called NEODyS, which is run by scientists who hunt for and study potentially hazardous asteroids. The site is intended to inform other astronomers of newly found asteroids, in part so that additional observations can be made. However, when 2001 PM9 was announced on NEODyS (Near Earth Objects Dynamic Site) on Friday, Aug. 17, it included odds of a possible impact in 2005 and 2007 that were better than 1-in-a-million. Slim, but not none. By early this week, the odds had been revised to none. Yet over the weekend, a handful of other Web sites disseminated the earlier information, some adding personal fears to their reports.

On a Web site called The Hot Sheets, a visitor posted details of the asteroid that included this warning: "Dear Readers, following are some facts that ought to set you right back in your chair, grow you some grey hairs - or cause a certain amount of lost sleep." Not the first time. While not widely published in the popular press, the case of 2001 PM9 mirrors other instances in which the public was warned of possible Earth impacts that later turned out to be no threat at all. The first and most infamous was asteroid 1997 XF11, which in 1998 was said to be on a course that might hit the planet in 2040. Most major news organizations reported the threat, which scientists later withdrew. The scenario was repeated in 1999, when asteroid 1999 AN10 was said to have a small chance to hit Earth in 2039. The release of that data, and subsequent publication by some media outlets, was criticized by researchers who still had a 1997 XF11 hangover and worried that their credibility was being eroded. NEODyS was created by a group of researchers at the University of Pisa in Italy - the same researchers who published the initial data about 1999 AN10. One goal was to provide better communication between scientists regarding asteroids, so that asteroid scares could be avoided.

But anyone can access the information, and other NEO (Near Earth Object) organizations also reported the initial 2001 PM9 data. The first reports of 2001 PM9 were disseminated by NASA's Jet Propulsion Laboratory (JPL) and another research group called Spaceguard Foundation. However, Donald Yeomans at JPL said his organization did nothing wrong. Though data on 2001 PM9 first appeared on JPL's Potentially Hazardous Asteroid list on Aug. 13, Yeomans said it was a "routine posting of orbital data and certainly not an announcement of any type of threat." No impact probabilities were listed on the JPL site, he said. "At no time did JPL formally or informally release any announcement about asteroid 2001 PM9," Yeomans said. "Our activities were restricted to requesting new data, soliciting archival data and working to compute updated orbits so the results could show, as quickly as possible, that this object was not a threat. We were rather proud that these activities took place so rapidly that by last Friday, the computations showed no real threat. That is exactly how things are supposed to work."

Brian Marsden is director of the International Astronomical Union's Minor Planet Center, which serves as the ultimate clearinghouse for data and names of asteroids and other small objects in the solar system. Marsden said scientists' ability to properly deal with early asteroid data has not improved since 1998, and the problem stems from how information is communicated. "This is not to say that NEODyS, or any other professionals working in the area, is doing bad science," Marsden said in comments today on a newsletter called CCNet, which provides a forum for discussing asteroid hazards. "It is very clear, however, that our community continues to flounder in the way such information is made public." Marsden was particularly critical of the fact that after the risk was found to be nil, a "risk page" about the asteroid was removed from the NEODyS site, rather than being updated to reflect the change. "Illogical though it may seem to us, some people tend to assume that such removal means that the object has in fact become more dangerous, not less, and that the astronomers are involved in a cover-up," Marsden said. "A simple posting to confirm that the object is no longer dangerous would work wonders."

Benny Peiser, a researcher at Liverpool John Moores University and the moderator of CCNet, said, "I wonder how many more asteroid scares it will take before the NEO community will heed the recurring calls for adjustment and make a determined effort to resolve this thorny issue." Efforts have been made. In 1999, the NEO community developed the Torino scale, a hazard index structured something like the Richter Scale for earthquake magnitude. The Torino scale was intended to improve definitions and communications between scientists, as well as their ability to communicate potential threats to the press and the public. But so far the Torino scale has been nearly nonexistent as far as the public is concerned.

According to scientists at NASA's Jet Propulsion Laboratory, there are currently 315 known "potentially hazardous asteroids," or PHAs. Each appears to be on a course that will one day bring it close to Earth's orbit, but scientists stress that none of them are known to be on a collision course with the planet. Many other asteroids that might be listed as PHAs are thought to be out there but not yet found. An asteroid capable of global disaster would have to be more than a quarter-mile wide, researchers say. Asteroids that large strike Earth only once every 1,000 centuries on average, according to NASA officials. Other estimates range widely, reflecting the fact that researchers don't know how many asteroids are out there, let alone how many might eventually cross the path of Earth. Smaller asteroids that are believed to strike Earth every 1,000 to 10,000 years could destroy a city or cause devastating tsunamis. Scientists have in recent years called on governments to begin making plans for how to defend the planet against such impacts.