Let’s say it is a starship/probe. I doubt there is anything we could do about it. Launch a nuke? Potential suicide. And if it is a Von Neumann type probe, it’s probably not the first by a long shot and may decide not to mess with the aliens that already arrived here hundreds, thousands, or millions of years ago. Just accelerate on to its next target star system.
I doubt there is anything we could do about it. Launch a nuke?
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No tto worry nothing we could launch would be able to catch up with it.