Very interesting.
My 6yo ds is very interested in weather -- a few months ago, he was very worried about tornadoes, hurricanes, tsunamis, etc. We live in Illinois! But it was still hard to get across to him that there was little/no danger of hurricanes in our part of the country; he was very concerned whenever he saw "cumulonimbus" on the horizon.
We got him several large and detailed books aimed at adults -- picture-heavy but also information heavy -- about inclimate weather, and he was hooked. Now he knows where hurricanes are likely to strike, why a tsunami won't get us in Illinois, etc. He's totally into it. He likes to cite statistics about the costliest weather disasters, the deadliest, etc., to anyone who will even half listen. And this is a kid who used to be terrified of that stuff.
I think his fear was a manifestation of what a hold that sort of weather had over his imagination, and that's why he likes it -- he relates to it in some way, and can confront his fear with knowledge. He still worries about tornadoes, but now he knows how to spot one and what the "danger signs" are, so he's less worried. He says he wants to be a "storm chaser" when he grows up.
From my experience, I would provide information -- lots of statistics about how very rarely big meteors hit the earth, and how scientists are working on the problem, and what he can do to help. The telescope is a great idea, I think! I'm guessing he can look to his heart's content and not spot the next "big one."
I'd get it for him! And then I'd supplement that with all sorts of other space information, if that's what he seems drawn to. Check out the adult section of bookstores or libraries; there are great photo- and information-heavy books on science subjects that work for HG+ kids at this age, who typically aren't satisfied with books aimed at their age group.
As acs said, it might make his fear worse ... but in my experience, the more info, the better.
