First, this goes under the heading of 'don't break the shared world'. It's common sense. If you try to break the earth, other authors are going to be unhappy. So there's already a rule for this.
Second, if somebody starts launching asteroids at earth, there will be a lot of people who notice. NASA keeps a close watch on the nearby sky. Amateur astrology is probably getting a huge boost with all the activity in the solar system. And there happens to be a significant population now orbiting the planet, including a bunch of over-active (and often bored) AIs. SOMEONE will notice the asteroids before they get here. And someone else will be more than happy to haul them into orbit for mining ('cause mining closer to your customers is more prophitable) instead of letting them go to waste by smashing into the giant gravity well (Earth/Mars/Venus/etc.).
If we're talking asteroids accelerated to extreme velocities (higher than .1c), then we have to ask: Who did it, and HOW? Accelerating something close to C is REALLY, REALLY tough. Doing it away from the sun, over a distance of lightyears, can be accomplished with solar sails and nifty engineering. Through the vastness of interstellar space, you can collect and use interstellar hydrogen. If you're trying to do it within the confines of this solar system, you're going to need LOTS OF ENERGY. Somebody's going to notice something like that BEFORE the asteroids start flying.
In other words, if somebody comes along and says, 'Oh, I'll just use accelerated asteroids', then someone (most likely Sirocco) will be right there to raise a fuss.
"Not this again!" Minerva said. "Albus, it was You-Know-Who, not you, who marked Harry as his equal. There is no possible way that the prophecy could be talking about you!" - Harry Potter and the Method of Rationality, Chapter 84
Second, if somebody starts launching asteroids at earth, there will be a lot of people who notice. NASA keeps a close watch on the nearby sky. Amateur astrology is probably getting a huge boost with all the activity in the solar system. And there happens to be a significant population now orbiting the planet, including a bunch of over-active (and often bored) AIs. SOMEONE will notice the asteroids before they get here. And someone else will be more than happy to haul them into orbit for mining ('cause mining closer to your customers is more prophitable) instead of letting them go to waste by smashing into the giant gravity well (Earth/Mars/Venus/etc.).
If we're talking asteroids accelerated to extreme velocities (higher than .1c), then we have to ask: Who did it, and HOW? Accelerating something close to C is REALLY, REALLY tough. Doing it away from the sun, over a distance of lightyears, can be accomplished with solar sails and nifty engineering. Through the vastness of interstellar space, you can collect and use interstellar hydrogen. If you're trying to do it within the confines of this solar system, you're going to need LOTS OF ENERGY. Somebody's going to notice something like that BEFORE the asteroids start flying.
In other words, if somebody comes along and says, 'Oh, I'll just use accelerated asteroids', then someone (most likely Sirocco) will be right there to raise a fuss.
"Not this again!" Minerva said. "Albus, it was You-Know-Who, not you, who marked Harry as his equal. There is no possible way that the prophecy could be talking about you!" - Harry Potter and the Method of Rationality, Chapter 84