Another commonly used trope in science fiction, especially the disaster movie, is the massive asteroid coming toward Earth. In this trope there is either nothing we can do about it, or we make every effort to avert disaster. The second response leads to either destruction of the Earth or salvation for the human species. And from the last, either the whole situation is resolved and life returns to normal, or some find a way to survive and the human race goes on. Now getting hit by an asteroid, or its colder cousin, the comet, is not a good way to start the day. It all has to do with the amount of force generated by a moving object, or the formula ½ M(mass kilograms) X Velocity (meters per second) Squared. As you can see by the formula, velocity is the most important component (squared after all is a big deal). Double the weight of the object and you double the force. Double the velocity and you do a whole lot more than double, you quadruple the force. A big rock hitting the Earth at a leisurely thousand meters a second is not such a big deal, unless you happen to be right underneath it. I use this as a threat in one of my novels, as an asteroid is supposed to be eased into Earth orbit and is set to drop on North America. Bad day for the United States, but the rest of the world (minus some coastlines) will come out of it A-OK. A really massive rock striking at hundreds of kilometers a second is an unmitigated disaster for everyone within thousands of kilometers. Want to know how big a disaster? Do the formula for kinetic energy, which gives the answer in joules, then figure how many joules make a big blast, something like a nuclear explosion. One megaton equals 4.18 X 10 to the 15th Joules. The bombs that leveled Hiroshima and Nagasaki, killing about a hundred thousand people each, were about one fiftieth this strength. A billion metric ton rock hitting at a hundred kilometers a second would be 5 X 10 to the 17th Joules, or 100 times the power of a one megaton bomb. The Dinosaur killer that hit the Yucatan Peninsula 65 million years ago was quite a bit bigger, much faster, and provided much more energy.
Now the best way to stop a large object from striking the Earth is to get out there and deflect its path so it doesn’t hit us. The further out the less energy actually needed, as the deflection is less. See, if the object is pushed a small distance off course that distance will multiply over time. If the object is close to Earth we have to use a lot more force to move it off course. So what does that mean as far as the trope is concerned that we see so often in movies and books?
The trope works very well in books from the past, like Lucifer’s Hammer and others, when space tech was still too primitive to do much. It even works well today, when we still aren’t able to do more than send some fragile probes out of the Earth-Moon system. Despite movies like Deep Impact and Armageddon, we would probably be toast if a big rock or iceball came flying at us out of the depths of space. But as soon as we are flying around the solar system or beyond on a regular basis, I really don’t think random rocks coming out of nowhere will be much of a threat. First of all we will see them coming. Second, we will be able to get to them and divert them at some distance from the Earth. I recently read a book in which colony ships were sent out to other solar systems to save humanity from an asteroid. Pure nonsense. If we could send a dozen ships out to other solar systems we would be able to move any asteroid, even one the size of Ceres, out of the way. And I also asked the question about other colonies in the solar system, or the establishment of such, given that the tech could get us to another star. The trope just doesn’t work with advanced tech. Unless someone is throwing multiple rocks at us as an attack. But that’s a different story.
I have actually thought of using the trope of the asteroid in a different manner in a novel, but it will have to wait for a different time, probably. What if a colony was to be established in another Solar System, and by the time they got there (slower than light you know) the perfect planet had been superheated and scoured of life by an asteroid hit. Now the colonists are faced with having to establish the kind of colony they weren’t equipped to do, like on an asteroid or lifeless moon. That would be something different in the hard science fiction realm.