system
Given the following post, respond as if you're commenting on Reddit:
human
If we were to harvest asteroids, could we simply slow them down enough to just drop them into our oceans without causing significant damage?

Given advancements in propulsion technology, I can't imagine dropping a huge asteroid near terminal velocity would be that devastating to the ocean or cause massive tidal waves. We used to test nukes in the ocean and they didn't destroy the land around them right?
gpt
If we slow down an asteroid so that it plummets onto the Earth, it will hit the Earth at something like escape velocity - about 11 km/s. It may slow down a bit during reentry, but that just means the kinetic energy is being transferred to the air directly instead of to the ground - the energy reaches the Earth's surface and atmosphere and causes damage regardless.

11 km/s means a kinetic energy of about 60 GJ/tonne. A megaton of TNT equivalent is about 4,000,000 GJ. So if the asteroid is around 100,000 tonnes of weight of less, its impact is in the range of megaton atomic bombs. But that is what you might expect from a typical near-Earth object, maybe <50m in size.

However, there is a wide range of asteroid sizes, and a significant number that are quite big - over 1 km in size. These easily get into the gigaton range of TNT equivalent, hundreds or thousands of times more powerful than the most powerful atomic bomb. These are not the most common type of asteroid, but there's a decent number of them. They're what we really need to watch out for.

Intentionally dropping smaller asteroids still probably is not *great* for the environment, but there we're getting into policy decisions rather than physics.