A decade ago, Slovic and some colleagues conducted a test. They provided a group of university students with information about the threat from beyond, explaining that a giant asteroid was thought to have killed off the dinosaurs, and others would surely hit the planet at statistically determined intervals. Then they surveyed the students to determine how they assessed the risk. The students recognized the threat, but chose not to worry about it.

"They're expectation was, well, it's not going to happen in my lifetime," Slovic says.

If astronomers were to announce an imminent collision, asteroids would suddenly develop a high Dread Factor, Slovic figures. But because none of us has any direct experience whatsoever with deadly space rocks, "People don't get worked up about it. There's too many things to worry about."

Scientists find it similarly difficult to generate much public worry for other potential calamities, like horrible storms, droughts and coastal flooding that might result over the next century due to climate change, but which are seen as remote in time.

Many astronomers, it must be noted, believe present asteroid search efforts are fairly adequate, notwithstanding the lack of a southern telescope. With time, they say, the worst threats will be rooted out, which is to say the largest asteroids. And, they argue, the odds are that if any globally destructive object is found to be on a collision course with Earth, there will probably be years of warning.

A more vocal group of astronomers and other proponents of increased spending tend to worry about smaller asteroids that could cause regional devastation. And they tend to make more frightening statements. Here are just a few that have come from the mouths of respected experts just in the past 10 days:

"If it were over a populated area, like Atlanta, it would have basically flattened it," asteroid cataloguer Gareth Williams told CNN in discussing the potential of asteroid 2002 EM7.

"We live in a cosmic shooting gallery," said Duncan Steel of Salford University.

"We're talking about a million megaton explosion," said author and physicist Paul Davies of Macquarie University, in discussing a typical impact on another recent television program. "That's a million city-bursting bombs all going off at once."

While such statements are often softened with the reminder that the world probably won't end tonight -- Davies said in the next breath, "I don't want people to lie awake at night worrying about it" -- the effort is clear: Get you and the politicians to act on this threat.

Yet in a world remade by a single day of terrorism, fear may be doomed as a sales pitch, just as it was in Australia.

Fear is not something that can necessarily be instilled by scientists. Instead, it tends to be generated by whatever rears its ugly head and shouts loudest, explains Robert Butterworth, a psychologist at International Trauma Associates in Los Angeles. Nothing right now, globally speaking, can measure up to the fear of terrorism and the associated potential of a nuclear attack.

While there are plenty of things for a 21st Century human to worry about, we all have our limits.

"In order for us not to have these things on our minds, we use a device that's been maligned in last few years, which is denial and repression," Butterworth says. "We push it back, because we couldn't function if we didn't."

Asteroids, like a fear of bugs or concern over a missed appointment, can be lost in a shuffle of frightening thoughts. Some things just aren't as significant as they seemed last summer.

Butterworth puts it this way: "If we had been walking with a limp and all of a sudden were shot in the stomach, the limp fades away."

No place has been hit in the stomach like New York City. Psychologist Janice Yamins, whose patients include victims of the terrorist attacks, says residents are stunned by their own change in views, such as newfound support for defense spending "instead of other things that won't help preserve our world."

Where fear leaves off, anger and revenge step in.

Natural disasters don't generate similar sea changes in philosophy. Californians suffer tremendously from earthquakes every few years. They pick up and move on. Southeast coastal residents rebuild time and again after hurricanes. People there shrug off the threat. Butterworth figures an asteroid impact would generate similar reactions.

"What do we do, shake our fist at God?" he asks. "Who can we be angry at?"

All this psychology lends support to a notion that has already formed in the heads of many astronomers: Their call for more funding will fall on a whole lot of deaf ears until another asteroid makes real noise.

The last serious impact was in 1908, when a rock about the same size as 2002 EM7 exploded above the surface of Siberia. Roughly 1,200 square miles (3,108 square kilometers) of forest were flattened in a remote region known as Tunguska. There were no known deaths, because almost no one lived there.

The odds of a similar event, which could easily destroy a large city or a small state with miles of extra destruction to boot, are about 1-in-20 over the next 50 years.

In the past decade, about 500 very large space rocks have been found to wander near the space shared by Earth's orbit. These so-called Near Earth Asteroids, all larger than 1 kilometer (0.6 miles), represent about half the expected total. Millions of smaller asteroids are almost entirely uncatalogued.

The larger rocks are the ones many scientists fear most. If one hit Earth, civilization would be pushed to the brink and perhaps beyond. Deaths could easily be counted in millions, possibly even billions. Many species of plants and animals would disappear.

As more asteroids are discovered and publicized, public awareness of the threat grows. But the information is not always accurate.

In a couple of high-profile cases, most prominently four years ago with an asteroid called 1997 XF11, the public was warned of potentially devastating impacts before further calculations showed the newly found rocks to be no threat at all.

Worse, late-night radio programs and various web sites spout all sorts of unscientific claims of impending asteroid doom, reports that spread like tsunami radiating outward from an ocean impact. Any reporter who covers the subject has gotten more than a few frantic e-mails from concerned citizens who heard this or that and were worried about the planet-destroyer coming next June, or whenever.

Movies like Armageddon only enhance "wild inaccuracies" in some minds, says Taylor of the Probability Research Group.

All of this -- the fact, the fiction, the unfounded fears and the genuine threats that some people don't fear at all -- create a gulf of apathy and misunderstanding that may well prevent asteroid experts from convincing you to see the world as they see it.

Several dozen professional astronomers, meanwhile, maintain a nightly vigil in the Northern Hemisphere, scanning immense and dark skies for tiny points of light, then struggling to observe often minor movements against the background of stars in order to determine a trajectory, an ultimate destination.

Always on their minds: Will this one hit Earth?

"It isn't a matter of if one of these things is going to hit the Earth," said Duncan Steel on the 60 Minutes broadcast. "It's just a matter of when. Either we can expect 23 years warning or six or seven seconds."

For those in the know, the asteroid Dread Factor is off the charts.