The Torino scale, developed in 1999 by Rick Binzel of the Massachusetts Institute of Technology, is used to inform the public about potential impacts. It rates an asteroid's threat on a scale of 0 to 10, based on its speed, size and probability of impact with Earth (see Graphic).No asteroid has ever exceeded a hazard rating of 1- the same chance as a random object of the same size hitting Earth in the next few decades.
Despite that, last week's category-1 asteroid made headlines. And as searches for near-Earth asteroids grow more systematic, sightings of potentially dangerous rocks are becoming routine. Even as the commotion over QQ47 was dying down, astronomers found another, even larger asteroid that earned a similar hazard rating. QQ104 is 2.7 kilometres across, and for a couple of days last week looked to be heading for a possible impact as early as 2009.
While journalists insist they reported the information on QQ47 accurately, astronomers feel they were misrepresented. "That was certainly much ado about nothing," says Steve Chesley of NASA's Jet Propulsion Laboratory in Pasadena, California. "It was like a virus solely within the realm of the press."
Binzel himself is so upset by the press coverage of asteroid scares that he is toning down the scale's wording. Instead of "requiring careful monitoring", a category-1 event will now be described as "normal". Brian Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, worries that the public will stop taking the asteroid threat seriously if false alarms continue. He says altering the scale isn't enough: "It's time we got rid of it." At the moment, newly discovered "threats" tend to start higher on the scale, when astronomers still have little information on them, and then drop down as further observations rule out the hazard.
Marsden says incorporating a measure of how long the asteroid has been tracked would help prevent false alarms. His colleague John Remo also believes the Torino and related Palermo scales have got it wrong. "They are scare indexes," he says. "They tend to create anxiety."
Rather than quantify the damage an asteroid will cause on impact, Remo says it would be more positive to rate how difficult an asteroid would be to deflect into a safe orbit.
But despite disagreements over how best to avoid crying wolf too often, astronomers insist keeping the data secret is not an option. "I hope people take away the idea that if there is actual news, it will be out in the open," says Binzel.
New Scientist issue: 20 September 2003.
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