system
Given the following post, respond as if you're commenting on Reddit:
human
What is the largest asteroid we could deflect in space?

Let's say today we discover an asteroid that will collide with the Earth in exactly 10 years from now. If it had apocalyptic capabilities, could we stop it? How small/how slow would it have to be for us to make it miss Earth?
gpt
Technically, we can't deflect an asteroid right now. It's possible, but we've never done it.

That said, (assuming we did have the technology), the longer we have the easier it is to deflect the asteroid. The orbit needs to be precisely measured It only needs to be slowed by a few minutes to completely miss earth in most cases. The heavier the asteroid, the more impulse is needed to move it. That means you need more propellant and a bigger rocket, which takes more time to assemble. If you have a long time you can use ion propulsion or a solar sail, which are much more efficient. I've even heard of an idea to use a really heavy probe to drag the asteroid in a certain direction without landing or impacting it.

If the asteroid is really close and you try to deflect it and fail it may land on a populated area instead of an ocean. If you don't have a good idea of how it's moving this chance increases.