Do I say anything?

How do you know that your GD hasn't had conversations about planets with her GF? They may have a joint interest in astronomy and why not?

Or not, as the case may be.

The trouble with a framed picture is that you can't easily trace it, you can't take it to school and pore over it at your desk, show your friends etc.

It's just going to be stuck there, on the wall.

Why intervene? as been said it wont be hanging on the wall forever, my younger grandaughter would have loved receiving that when she was younger. Perhaps your gd asked her grandad for that for her birthday because she knew no one else would buy it for her.

An eight year old girl will most likely want to decorate her room in a completely different manner. Anyway, blu tack is the usual method of attaching that kind of thing to walls at that age.

Be ruthless. Tell him to ditch the frame, or not be surprised if GD keeps it under the bed. Or in the shed.

Not fair on anyone really. Men! Why do they have this tunnel vision?!

Would be a lovely present, presented rolled, as a reference map.

Say nowt. This is not really a problem and I agree that a bit of over-thinking is going on. I would simply be delighted if my OH bought my GC anything at all - so far it has all been left to me!

Sorry, but I think you are over thinking things.
If I bought my GS a present I wouldn't expect it to be displayed forever.
If he is an eight year old I would hope he could arrange his bedroom as he wished and he would be more than capable of getting it out of the frame if he wanted.
Give it to him as is and let him decide.

hmmmn, tricky one! Is your DGD interested particularly in planets, the solar system etc?If so, she may like it, but if not.....
A well meaning but misguided present perhaps.I would not say anything to your DH though today to spoil things, but later have a quiet word with your DD.