system
Given the following post, respond as if you're commenting on Reddit:
human
[General Sci Fi] Planetary defense against relativistic kinetic weapons?

Relativistic kinetic weapons (also known as relativistic kill vehicles or RKVs) are a hypothetical means of interstellar warfare. An RKV is simply a heavy mass (say a car-sized hunk of steel) that is accelerated to close to the speed of light and aimed at a planet. Each such object will have a COLOSSAL amount of kinetic energy and, depending on its mass and speed, will hit the planet with the energy of a nuclear bomb, a dinosaur killer asteroid, or worse. Hundreds or thousands of these could be fired at a planet. Their small size combined with their extreme speed would make their interception or even detection exceptionally difficult.

RKVs are featured in a novel called *The Killing Star* wherein Earth is the target of a massive RKV attack. It does not go well for the earthlings.

My question is **how do you defend a planet against relativistic kinetic weapons?**
gpt
Large gravitational forces would be your safest bet.. Say objects the size of the moon placed between you and the incoming attack could exert enough gravitational pull to cause the weapon to miss but you'd need to have that object dangerously close to earth or be able to deploy it after the weapon is targeted and fired but before it can be adjusted to compensate which would be unrealistic. If you have the technology to move a moon sized object to redirect gravity it'd be easier to use that tech to stop the incoming weapon than to move a moon.  

Second option would be to intercept the incoming weapon with either one of your own or possibly a large object with enough density to alter it's course.  Either shoot a similar enough object to halt it's momentum at a safe distance which being near light speed would be only a few moments to notice the incoming weapon target it and fire at it which is possible but highly unlikely.  You could fill the space around earths orbit with massive shield objects or ships but you'd need to anticipate where it was coming from or fill the entire orbital path with objects and you'd still have massive holes in coverage.  

If technology is available create a blackhole the size of a softball in orbit around pluto it's gravitational pull should interfere enough to make extrasolar targeting near impossible without causing too much damage to our solar system in the next thousand years.