Danger zones. Values 8, 9, and 10 represent a certain impact.

And Now, the Asteroid Forecast ...

Astronomers have devised a scale to rate the danger posed by asteroids headed for Earth, comparable to the Richter scale of earthquake fame. The so-called Torino scale, which ranges from 0 (no collision) to 10 (certain collision causing Earth-wide devastation), was developed by Richard Binzel of the Massachusetts Institute of Technology and presented to colleagues during a June workshop in Turin (Torino), Italy. The International Astronomical Union will endorse it in a statement tomorrow.

The topic of asteroids is "prone to sensationalism," says Binzel; twice in recent years a media hype erupted after astronomers discovered a rock that had a remote possibility of slamming into Earth within 50 years (ScienceNOW, 11 March 1998 and 20 April 1999). "It's very hard to communicate extremely low probabilities to the general public," says Binzel. "The new scale gives us a common lexicon."

The scale, which Binzel had been working on since 1994, takes into account the chances an asteroid will hit as well as the possible collision's kinetic energy, which is determined by the asteroid's size and speed relative to Earth. Torino scale values of 8, 9, and 10 refer to certain collisions, with local, regional, and global consequences respectively. Just as no Californian would be alarmed by the prospect of an earthquake registering 1 on the Richter scale, "the average citizen shouldn't be concerned about an asteroid with a Torino value of 1," says Binzel. The two recently discovered asteroids both would have been rated 1 after they were first discovered, but subsequent observations would have placed them firmly in the 0 category.

The scale hasn't been tested with the general public, but Binzel says he was advised by science writers Kelly Beatty of Sky & Telescope and David Chandler of The Boston Globe. "In formulating the scale, we tried to be sociologists as well as scientists," he says.

But will astronomers adopt the new scale? "This will have to sink in a little bit," says Tom Gehrels of the Lunar and Planetary Laboratory of the University of Arizona, who heads one of the projects searching for near-Earth objects. "I think we ought to use it," he adds. Carl Pilcher of NASA's Office of Space Science calls the Torino Scale "a major advance in our ability to explain the hazard posed by a particular [object]." In the end, Binzel hopes that it may also raise public awareness and lead to more funding for asteroid searches. "Already, we're beyond the giggle factor."