As if there weren't enough earthly worries these days, fifty or so people gathered on campus November 7 to hear about an altogether different kind of threat - the peril posed to life on earth by objects from space. The wake-up call came from Sir Crispin Tickell, a genteel, silver-haired former British permanent representative to the United Nations and coauthor of the recent report "Potential Hazardous Near Earth Objects." The menace he described is frequently dramatized in movies - Deep Impact and Armageddon most recently - but Tickell cautioned that the danger of asteroids and comets is not just the stuff of fiction. ("Man-made satellites could be a nuisance," he told the audience, "but they're not going to blow up the earth.")

"We and all living creatures are living dangerously on the earth," Tickell said in a speech titled "Impacts from Space: Past, Present, and Future." "Only the shortness of our lives shields us from how vulnerable the earth is."

Tickell warned that the risk of being killed by an asteroid is only slightly lower than that of dying in a plane crash. And while the comparison may have gained resonance since September 11, Tickell admitted that the possibility remains extremely remote. Still, he called for a coordinated international effort to study the extent of the threat and ways to prevent major impacts. To fail to do so, he said, would be greatly irresponsible (not to mention that it would leave the human race vulnerable to the same fate that befell the dinosaurs). Tickell said he hopes it doesn't take a tragedy to focus attention on the destructive potential of extraterrestrial objects. But even disasters sometimes have benevolent effects.

"You don't want your catastrophe to be too big or too small, too fast or too slow or to affect anyone in this room," he said. "But catastrophes can help produce change.