I always see lots of information about asteroid impacts, but very little is said about comet impacts. As I see, a long period comet impact is much more dangerous because a) we wouldn't have time to prepare for it, and b) even small bodies would have high kinetic energy, equivalent to large asteroids.
On the flip side, I think that a long period comet would have trouble hitting the Earth, as it wouldn't have time to interact with our planet as an asteroid does. It would just hit us if, by chance, it was crossing the ecliptic plane at 1 AU from the Sun and we happened to be at the same place as well. So, my question boils down to the following:
- Do long period comets cross the ecliptic plane at a preferential distance from the sun (or: what is the chance of them crossing at approximately 1 AU)?
- What is the area of the hitting plane, versus the cross section of our planet?
- Does the assumption that a comet wouldn't have time to interact with us holds?