Bad Astronomy. Misconceptions and Misuses Revealed, from Astrology to the Moon Landing 'Hoax'

asteroids do indeed exist.) In the same year, the movie Deep Impact depicted a comet getting shattered by a bomb shortly before it entered the Earth’s atmosphere. That’s even worse! Instead of a single impact yielding an explosion of billions of megatons, you’d get a billion impacts each exploding with a yield of many megatons. In his fascinating book, Rain of Iron and Ice (New York, Helix Books, 1996), University of Arizona planetologist John Lewis calculates that breaking up a moderately sized asteroid can actually increase the devastation by a factor of four to ten. You’d spread the disaster out over a much larger area of the Earth, causing more damage.

If we cannot blow it up, then what? Of course, the best option is for it to miss us in the first place, so we’d have to shove it aside. The orbit of an asteroid can be altered by applying a force to it. If enough time is available, like decades, the amount of force can be small. A larger force is needed if time is short.

There are several plans for pushing such rocks out of the way. One is to land rockets on the surface and erect a giant solar sail. The sail, made of very thin Mylar with an area of hundreds of square kilometers, would catch the solar wind and also react to the minute pressure of sunlight. It would impart a gentle but constant force, moving the rock into a safer trajectory.

Another plan is more blunt: attach rockets to the asteroid and use them to push it. This has the engineering difficulty of just how you’d strap boosters to a rock in the first place.

Ironically, Hollywood came close to another good plan. Instead of blowing the rock up, we use nuclear weapons to heat the asteroid. Again, in Rain of Iron and Ice, Lewis finds that a small nuclear explosion (he implies a yield of about 100 kilotons) would suffice. Exploded a few kilometers above the surface, the intense heat of the explosion would vaporize material off the surface of the asteroid. This material would expand outward, and, like a rocket, push the asteroid in the other direction. Lewis mentions that this has two benefits: it prevents the impact, and also removes a nuclear weapon from the Earth. This is the favored method of all the people who have studied it.

All of these methods have a subtle assumption attached, that we understand the structure of asteroids and comets. In reality, we don’t. Asteroids come in many flavors; some are iron, some stony. Others appear to be no more than loose piles of rubble, barely held together by their own gravity. Without knowing even the most basic information about asteroids, we are literally shooting in the dark.

As with most problems, our best weapon is science itself. We need to study asteroids and comets, and study them up close, so that we can better understand how to divert them when the time comes. On February 14, 2000, the NASA probe Near Earth Asteroid Rendezvous entered orbit around the asteroid Eros. The amount learned from the mission is astounding, such as the surface structures and mineral composition of the asteroid. More probes are planned, some of which are ambitious enough to actually land on asteroids and determine their internal structure. We may yet learn how to handle dangerous ones when the time comes.

There is an interesting corollary to all this. If we can learn how to divert an asteroid instead of merely blowing it up, that means we can steer it. It may be possible to put a dangerous asteroid into a safe orbit around the Earth. From there we could actually set up mining operations. Based on spectroscopic observations of meteorites and asteroids, Lewis estimates that an asteroid 500 meters across would be worth about $4 trillion in cobalt, nickel, iron, and platinum. The metal is pure and in its raw form, making mining relatively easy, and the profit from such a venture would be more than enough to pay off any initial investment. And that’s a small asteroid. Bigger ones abound.

Science fiction author Larry Niven once commented that the reason the dinosaurs became extinct is that they didn’t have a space program. We do, and if we have enough ambition and enough reach, we can turn these potential weapons of extinction into a literal gold mine for humanity.

Until then, we don’t have too many options. Maybe we can divert the big one when the time comes, but for now all we can do is imagine what an impact might be like. Unfortunately, movies have had their own impact. Anytime an unexplained phenomenon involves something falling from the sky, meteors are usually blamed.

Which brings us back to the Ayoubs, still searching for a meteorite in their backyard in Salisbury, New Hampshire. Initially, this night visitor sure did sound like the usual description of a meteorite. But my knowledge of their behavior was telling me otherwise. As I said, meteorites won’t cause fires unless they are very big. But other things didn’t add up, either. The path was described as an arc, while a meteor’s trajectory would have been straight down. Also, no meteorite was ever found, despite a dedicated search. I mentioned to the property owner that meteorites can be sold for quite a bit of money, so he had strong incentive to find it. I never heard of anyone finding anything.

In the end, these events usually have some mundane, terrestrial cause. I would bet money that it was someone setting off fireworks in the thick woods near the Ayoubs’ house. This is a guess on my part, and it may be wrong. We may never know what started those fires, but we know what it wasn’t. We can blame Hollywood for our mistaken understanding of meteorites, but we can’t blame everything else on the poor things themselves.

16. When the Universe Throws You a Curve: Misunderstanding the Beginning of It All

Astronomy sometimes has a way of making people feel small.

For most of our history we humans have been pretty self-important. We believe that the gods pay special attention to us, even intervening in our daily affairs. We claim territory for ourselves, and ignore what goes on outside those borders. Why, we’ve even said the whole universe revolves around us!

But the universe is under no obligation to listen to our petty boasts. Not only are we not at the center, but also there really isn’t a center at all. To see why, we need to look into the past a bit, back into our own history.

For thousands of years it was thought that the Earth was the center of the universe and the heavens spun around us. Certainly, observations support that belief. If you go outside and look up for even a few minutes, you’ll see that the whole sky is moving. But you don’t feel any movement, so clearly the Earth is fixed, and the sky moves.

Even today, when we know better, we still talk as though this is the way things are: our vocabulary reflects the geocentric universe. “The Sun rose at 6:30 this morning” is less accurate that saying, “From my fixed location on the surface of the spherical Earth, the horizon moved below the apparent position of the Sun at 6:30 this morning.” But it is easier to say.

This Earth-centered model was fine-tuned by the Greek astronomer Ptolemy around a.d. 150 or so. People used it to predict planet positions, but the planets stubbornly refused to follow the model. The model was “refined” — that is, made more complicated — but it never quite made the grade.

Eventually, a series of discoveries over the centuries removed the Earth from the center of the universe. First, Nicolaus Copernicus presented a model of the solar system in which the Earth went around the Sun, rather than vice-versa. His model wasn’t really all that much better than Ptolemy’s model at figuring out where the planets would be. But then Johannes Kepler came along a few centuries later and tweaked the model, discovering that the planets orbit in ellipses instead of circles, and things were a lot better.

So with Copernicus’s model it looked like the Sun was the center of the universe. That’s not as good as having the Earth there, but it’s not too bad.

Then around the turn of the twentieth century, Jacobus Kapteyn tried to figure out how big the universe was. He did this in a simple way: he counted stars. He assumed that the universe had some sort of shape, and that it was evenly distributed with stars. If you saw more stars in one direction, then the universe stretched farther that way.

He found an amazing thing: the Sun really was the center of the universe! When he mapped out the stars, the universe was blobby, like an amoeba, but it seemed to be fairly well centered on the Sun. Maybe the ancients were right after all.

Or not. What Kapteyn didn’t realize is that space is filled with gas and dust, which obscures our view. Imagine standing in the middle of a vast, smoke-filled room, like an airplane hangar. You can only see, say, 20