Letters

Bustin' Asteroids
The article by Tony Ortega ("Eclipsed," February 25) has a devious distortion of an interview. Our LINEAR colleagues have been reporting on their detectors for the U.S. Air Force for more than a decade, freely and in detail. I told Ortega this, and I told him all of the following. Whenever I heard a presentation by Grant Stokes and his colleagues at a conference, I made it a point to encourage them to prove their detectors by finding asteroids near the Earth. They are doing that now, and I think it is great. Their advance and great success have helped us to obtain better detectors for Spacewatch, too.

Tom Gehrels
Tucson

As someone deeply involved in the science of the impact hazard, I want to say a couple of things about your story about Tom Gehrels, LINEAR, etc. First, it was fun to read and was basically accurate.

There is one important area, however, that it misrepresents, through a combination of some simple and common mistakes and possibly because of some hype on the part of people you interviewed.

You say that a one-kilometer-size asteroid is large enough to cause a "mass extinction." This, of course, is not true. The well-documented mass extinction 65 million years ago was because of an asteroid (or comet) roughly 10 times as big (or 1,000 times more mass, hence, 1,000 times the energy).

It is generally accepted that a global environmental disaster might be caused by the impact of a mile-wide (1.5-kilometer) asteroid or larger--one that might threaten worldwide agriculture and possibly destabilize civilization, resulting perhaps in a billion deaths. Gehrels exaggerates a bit, I believe, in reducing this "threshold size" asteroid to just a kilometer. But you make a mistake in the implicit assumption that such a global environmental disaster would kill everyone on Earth, which is what you do when you assume that an individual will necessarily die if such an impact happens and compare it with the risk of death in more common accidents.

David Morrison (of NASA Ames) and I have estimated that a quarter (not all) of the world's population might die in an impact by an asteroid larger than 1.5 kilometers. That turns out to imply a chance of dying by impact of about 1 in 20,000, which is approximately the risk of dying in an airplane crash.

Another mistake you make is in assigning the probability of dying in an automobile crash at 1 in 5,000. It is actually much greater for the average American, about 1 in 100. By associating the impact hazard and automobile hazards, you make the impact hazard seem much greater than it really is.

And it takes a fantastically larger (and much more unlikely) impact to actually cause a "mass extinction," which is the total and permanent wipeout of many species of plant and animal life.

These enormous consequences and minuscule probabilities are difficult for people to understand, and you are hardly alone in getting a bit mixed up about the numbers. However, if society is to make some rational decisions about how seriously to take this threat from the skies, it is important not to make mistakes of a factor of 50 (in the automobile death rate) or 1,000 (in the case of the difference between a civilization-threatening impact and a mass-extinction event).

Clark R. Chapman
Southwest Research Institute
Boulder, Colorado

I laud Tony Ortega's recent article regarding the search for asteroids potentially threatening Earth. The article was well-researched and well-put-together. This type of in-depth journalism is what New Times does best. To do it on subjects related to the natural world in addition to your usual grist of politics, dirty corporations and the arts is refreshing and greatly appreciated. Thanks for the great effort. I look forward to more.

John Gunn
Mesa

In your apparent quest to alarm the public, you have suggested that the likelihood of a person being killed by an asteroid is similar to the likelihood of a person being killed in an auto accident. However, the reality is that you compared the odds of a person being killed at any time during his 66-year life span by an asteroid with the odds of a person being killed in an auto accident during one particular year. A person is 66 times as likely to die in an auto accident as he is to die by virtue of a killer asteroid striking the Earth. Rather less frightening than your claim.

Dana Weick
via Internet

The story of Brian Skiff and the asteroid hunters was very good! Kudos to a story well done!

Tracy Wilson
Atlanta, Georgia

I'm puzzled about the purpose of the asteroid story by Tony Ortega as well as not much impressed by the quality of his writing.

Is the purpose to suggest there is some sinister plot by sneaky folks in New Mexico to undermine the work of upstanding Arizona residents? That argument is similar to moaning about computers and word-processing software replacing typewriters. Some still have not adjusted to the perceived great injustices inflicted by technological advances. I don't see any difference between typewriters being replaced and a more efficient way of finding asteroids coming into use. But for some reason, New Times thought that old saw was worth a cover story. Did I miss something? Was there some other purpose in the story?

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