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Asteroid "Near" Miss: False Alarm or Wake Up Call?

     March 11, the day my last column ran, will no doubt be remembered as one of the most significant dates in science this year. The importance of this date, of course, has nothing to do with my column. At the same time one or two of you may have been reading Relatively Speaking, It's All About Time, members of the press around the world were reading a disturbing release written by Dr. Brian G. Marsden of the International Astronomical Union. Orbit calculations for a recently discovered asteroid predicted that on October 26, 2028, the mile-wide asteroid would pass within 50,000 kilometers of Earth (closer than the moon), possibly even colliding with Earth. Such a collision would likely be the worst disaster ever to strike humankind!

      The very next day, though, NASA's Jet Propulsion Laboratory released a statement saying new calculations had shown that in 2028 the asteroid would miss Earth by nearly a million kilometers, so there was no chance of a collision. Many headlines around the world were not kind to scientists after this "false" alarm--Is the sky falling? Let's check the math first (Houston Chronicle), Asteroid experts postpone the end of the world (The London Times), Okay, so they were a little off (U.S. News), Big asteroid, even bigger mistake (SF Examiner). How could the first release have been so wrong? 

Science and the Press

      Well, actually, it wasn't. Orbit calculations are based on measurements of certain observations. The more observations we have of an object in space, the greater the accuracy of orbit calculations based on those observations. The asteroid was just discovered this past December, so the observations were somewhat limited. The calculations (unless they truly contained an error), were the most accurate available at that time. In the original release, Marsden suggested that the asteroid may have been noticable in certain past years but had gone undetected; older photographs might give more accurate data. The next day, following the suggestion, NASA scientists found the asteroid in 1990 photos and included that data to calculate the more accurate orbit.

      The press tended to report the more sensational parts of the original release. Emphasized were a collision "is not entirely out of the question," and "The object could come significantly closer than 30,000 miles." Seldom reported were the phrases "The chance of an actual collision is small," and "There is still some uncertainty to the computation." The image then, portrayed by many (but not all) media was that scientists had bungled calculations and scared everybody with a fasle alarm.

      On the contrary, though, I think this is a good example of how science works. Observations were made about something in the natural world. A conclusion was made based on the observations. New observations, which would support or invalidate the original conclusion were suggested. Those observations led to a new, more reliable conclusion. This is how science is supposed to work.

      Scientists are human, of course, and must take some of the blame for the "Chicken Little" take on the asteroid story. Sometimes, the competitive nature of scientists (there is much glory in being the first to discover something of scientific importance) causes scientists to rush to release preliminary findings. This asteroid was not due for thirty years, what harm would there have been in checking for prediscovery observations before issuing an official press release? Finally, the response of the press, right or wrong, was predictable. Press releases could be written in a manner that maintains the "factual" nature of the information but anticipates and minimizes potential sensational responses.

      But enough commentary on the nature of science, scientists, and the press. Let's get back to asteroids. 

How real is the threat?

      A large, massively destructive asteroid impact is very unlikely in our lifetime. Yet in the long run, such an event is a certainty! A pair of binoculars and a full moon are all that are needed to confirm this. Unlike the Earth, the moon has a stable surface. With no atmosphere, the moon's surface is not subjected to the erosive forces of wind and water. The moon has been geologically stable for three billion years (no new mountains formed, no major faulting or shifting on the surface).

      About one-sixth of the moon's surface consists of smooth regions known as "seas." These seas show a visible record of surface disturbances over time. Impact craters from five asteroids big enough to destroy much of life as we know it on Earth can be clearly seen in these seas. Since such collisions are random, it is reasonable to assume that around thirty (five per sixth) major asteroids have hit the moon since its surface stabilized. And the moon is a much smaller target than the Earth!  

The Danger of Asteroids

      The real danger with a potential asteroid collision is the speed with which asteroids travel. Truly faster than a speeding bullet, a large asteroid would release enough energy in its explosion to cause a tremendous loss of life. Convincing evidence indicates such an impact was responsible for the extinction of the dinosaurs 65 million years ago. In fact, a major asteroid may hit the Earth on average every ten million years. Although slim, those are better odds than some lottery players face! 

Detecting Asteroids

      Astronomers are focusing now more than ever on finding and mapping potential hazardous asteroids. Only a small percentage have been discovered, and the process is slow. The recent public focus on the possibility of an asteroid impact, though, may lead to more funding for asteroid detection research. Two upcoming summer movies, Armageddon and Deep Impact (basic plots: big-hearted heroes versus bigger asteroids) attest to the timeliness of planning for the possibility of an asteroid collision. 

Can We Stop an Asteroid?

      Suppose scientists discover an asteroid that really is likely to collide with Earth. What can we do to stop it? No one really knows, but there are two lines of thought: move it or destroy it. Perhaps, by landing on it and attaching rockets to it or bombarding it with rockets from the side, we can push the asteroid  off course enough to miss us. Or, if that does not work, then perhaps we would try to destroy the asteroid with nuclear weapons. In all likelihood, we will test some of these ideas on a close-approaching asteroid sometime in the future.

       We can look at the moon and count the impact craters. The fossil record whispers to us about an asteroid that may have killed the dinosaurs. Other mass extinctions in Earth's history hint of asteroid involvement. We all saw comet Shoemaker-Levy 9 crash into Jupiter. In 1989, an asteroid surprised scientists with a close pass by the Earth. We do not need to panic, but we do need to be prepared. Let me paraphrase a leading astronomical group's position paper on the potential threat of an asteroid impact: What greater feat could there be than to perhaps someday alter the course of an asteroid to prevent an impending disaster? And what greater tragedy, given our knowledge and abilities, than to be caught unprepared?

2006  Dirk Oden



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