the sky is falling! The sky is falling! Well, at least during the month of February -- television's sweeps month. The tube is suffering from major apocalyptic-impact overload these days, what with NBC's four-hour "Asteroid" concluding Monday night, a cheery Valentine's Day special titled "Doomsday, What Can We Do?" on Fox, an earlier Discovery Channel broadcast of a British documentary called "Three Minutes to Impact" and an upcoming National Geographic special on big-rocks-hit-Earth. There's even talk that Steven Spielberg is at work on a film called "Deep Impact," based on the Arthur C. Clarke novel "Hammer of God."
Network programmers and editors (The New Yorker ran a cover story by science writer Timothy Ferris on asteroids) have just discovered a subject that has fascinated astronomers even before they realized that it was a space rock crashing into Earth that killed off the dinosaurs millions of years ago. These days, astronomers call comets and asteroids -- the garbage left over from the big bang -- "Near Earth Objects." And since comet Shoemaker-Levy blasted the surface of Jupiter in a series of fireballs two years ago, their interest in these unwelcome chunks of astral matter has become a bit less theoretical.
Are we really in for the really big disaster? Should we be building a Star Wars weapon to knock a speeding asteroid off course? In an attempt to find out if the truth really is out there, Salon spoke with Dr. David Morrison of the Office of Space at NASA Ames Research Center in Mountain View, Calif.
All these movies and documentaries on asteroids -- are they millennium hysteria, or should we be heading for the hills?
We should be concerned about it because it is a very real, natural hazard and one that we need to understand. There's no question, over time, that Earth will be hit many times by objects large and small, including ones as large as the one that did in the dinosaurs. The survival of humanity depends on us understanding and protecting ourselves from such impact.
We're already receiving small hits on a regular basis?
We get hit by something with the energy of the Hiroshima atom bomb about every week or two. Fortunately, these all break up and explode high in the atmosphere, so they do no damage on the ground. They blow up very high and are observed regularly by the Defense Department's satellite. Something that does real damage to us happens, on average, every few hundred years.
Including this century?
Yes, in Tunguska in Siberia. In 1908 a stony meteorite of about 15 megatons blasted more than a 1,000-square-mile area and killed one person. It would have killed more, but it was a place where nobody lived. The unlucky victim was picked up by the blast wave, smashed into a tree and pierced by a limb on the tree.
Statistically, when could we be in for a similar-sized event?
Any time. You don't have a grace period following an impact. The chances in any one year that we'll be hit by one large enough to produce a global catastrophe -- but smaller than the one that destroyed the dinosaurs -- is about one in a million.
What kind of damage would it cause?
It would not produce a global firestorm and mass extinction, but it would produce a climate fluctuation that would lead to crop loss and mass starvation, perhaps killing a billion people.
Leaving human civilization as we know it ...
Not in very good shape.
What do scientists believe wiped out the dinosaurs 65 million years ago?
An object about 10 miles across landed in shallow water in the Yucatan area, creating an immediate impact 150 miles across. It also created a large tsunami wave which contributed to the destruction. But the big effects were not local, they were global. The plume of ejected material fell back down over the whole planet and in re-entering the Earth's atmosphere was heated to incandescence and produced a global firestorm. Nearly all the grasslands and forests of the Earth caught fire. The dinosaurs were probably made extinct in half an hour. The dust that was injected into the atmosphere lasted about a year, blocking out sunlight and causing a drop in temperature. The whole chain of food production stopped.
Like a nuclear winter.
Only worse.
Do you think there's more cause for alarm now, after Shoemaker-Levy?
I would not use the term alarm. Concern is a little more like it. We don't know of any object heading toward the Earth right now, and the chances that there will be a catastrophe next year are quite small. But it would be prudent to carry out a survey and see if there really is anything headed our way.
Actually watching 20 pieces of a comet crash into Jupiter and seeing the dramatic effects of those impacts was a sobering thing for scientists and should be for lay people as well.
What do we know about what's cutting through our orbit now?
There are about 50,000 pieces that are 300 meters in size, the size of three football fields. There are some as big as 10 miles in size, and others in between.
You've spoken of the need for more study of what's out there. How many astronomers are engaged in this work now?
A handful. My usual phrase is less than the staff of a McDonald's restaurant. There are two international teams operating, one in Arizona and one on Maui.
In your work as chair of the Spaceguard Survey in 1992, you reported to Congress that we would need three or four telescopes scanning the heavens at a cost of about $5 million a year for 10 years to do a complete study. Assuming this work was funded, what do you think you'd find?
Chances are we'd find that none of those objects pose us any threat. But we won't know until we look.
And if we found a rather large object ...
If we found an object that did threaten us, then I have no doubt that we would use our technology to develop a defense system and would actually use nuclear explosives to change its orbit so it would miss the planet entirely. This is the only natural hazard that we know how to protect against. The debate is whether we should go ahead and develop such a defense system in advance of discovering such an object.
The late Carl Sagan, for one, was opposed to it.
Sagan said if you have the technology to steer an asteroid away from the Earth then you would also implicitly have the technology to place one into an Earth collision orbit -- if such a technology fell into the hands of a madman.
The counter-argument, which I feel is correct, is that the technology we're talking about is very crude. You could not characterize it as "steering" an asteroid. So there's no danger of that technology being used to precisely adjust the orbit of an asteroid to make it into a weapon. Maybe, long in the future, if we really ever did have the technology to make these minute adjustments in orbit, Sagan's concerns would be legitimate, but it's not relevant to the concerns we have right now.
And you feel that our technology is good enough as it is to avert catastrophe?
Yes.
Some people have suggested that a Near Earth Object was responsible for the crash of TWA flight 800.
Certainly there's a chance. Given all the uncertainties around the TWA crash I don't think we can exclude the possibility that it was hit by a meteorite. That's not very likely, but it seems that they haven't had much luck with the other hypotheses either. I think it's reasonable to at least ask the question of whether that might have happened.
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