When Comet Shoemaker-Levy 9 broke apart and slammed into Jupiter in 1994, earthlings had front-row seats to a spectacle their own planet hadn't seen in 65 million years.
Now, a growing number of astronomers are asking that people start giving serious thought to how to deal with the threat of an impact on Earth.
Researchers have made substantial progress in identifying larger near-Earth asteroids. They now are contemplating building a telescope that would allow them to spot smaller near-Earth asteroids - space rocks that could inflict substantial regional damage if they struck.
But to Daniel Durda, an astronomer with the Southwest Research Institute, it's time to focus on dealing with the threat - from identifying which official or agency gets the first phone call when a threatening object is identified to establishing plans for coping with the aftermath of an impact.
"Scientists have focused on physical and technical issues" surrounding the threat from near-Earth asteroids (NEAs), says Dr. Durda. "But there's been a hole in the discussion - the human aspects of the threat."
As if to underscore the havoc that impact events can wreak, researchers from the University of Washington and the University of Rochester recently published a study concluding that a giant asteroid or comet probably contributed to the largest mass extinction in Earth's history.
The extinction marked the transition from the Permian to the Triassic period 250 million years ago. More than 90 percent of all marine species vanished. On land, widespread extinctions cleared the way for the rise of dinosaurs - themselves done in by an impactor 65 million years ago.
The team's "smoking guns" lie within tiny soccer-ball shaped formations of carbon found in 250 million-year-old rock. The formations trapped forms of helium and argon more similar to those found in meteorites than in Earth's rocks.
Durda acknowledges the difficulty of trying to focus public and political attention on a natural hazard that is rare, but devastating. "People know an impact is going to happen, but not tomorrow," he says. "This gives them the weasel room to put off thinking about it."
Even near misses can pose challenges.
In a recent report, Durda and Clark Chapman, also of the SWRI, and Robert Gold of Johns Hopkins University, note that a close brush with a comet's tail could destroy many of the communication satellites orbiting Earth - satellites critical to economic activity worldwide.
Nor are US scientists alone in calling for national and international efforts to develop approaches to dealing with the threat or the aftermath of an impact.
Last year, Britain's Parliament established a scientific commission to look at the near-Earth objects (NEOs) issue. And last month, the government responded to the commission's report by promising to work more closely with the European Space Agency on the issue. It apparently declined, however, to pay for a new telescope to search for near-Earth objects or to establish a center for them.
The lion's share of search work is done by the US, and more "glass" is being applied to the effort. Last fall, the Spacewatch program, headquartered at the University of Arizona, finished work on a 1.8 meter telescope on the summit of Kitt Peak, near Tucson. Astronomers also have given a high priority to building an 8.4 meter telescope that, among other projects, would attempt to catalog 90 percent of near-Earth asteroids greater than 300 meters across within a decade.
Astronomers have been working to catalog NEAs that are 1 kilometer across or larger. So far, they have found approximately 50 percent of these asteroids, according to David Morrison, with the National Aeronautics and Space Administration's Ames Research Center in Mountain View, Calif.
Dr. Chapman, Durda, and Dr. Gold argue that it's time to augment these surveys with efforts to plan for the day when astronomers discover a speeding space rock with Earth's name on it. One critical step, they say, is to be prepared to send unmanned probes to the asteroid to study its composition and structure. The recently concluded Near Earth Asteroid Rendezvous mission represents the kind of effort that would be needed, they say.
Armed with such information, researchers would be in a better position to recommend ways to deflect or even destroy the asteroid.
The trio holds that the key to coping lies in bringing a broader range of expertise to bear on the issue and not just leaving it to astronomers. Climate modelers, seismologists, meteorologists, emergency response planners, and other groups have expertise that would bear on attempts to prepare for an impact.
"The dinosaurs could not evaluate and mitigate the natural forces that exterminated them," the authors write, "but human beings have the intelligence to do so."
(c) Copyright 2001. The Christian Science Monitor