I have now played two matches with multiple planets in which there are celestial bodies in different orbits and it would not allow me to use nukes on planets in a different orbit as mine like in the screenshot provided. I was able to nuke my nearby moon but was unable to nuke any of the inner planets.
Nukes won't orbit the sun they work from planet to moon or moon to planet. Not Planet to planet. for that matter I don't even think you can fire from one moon to another moon of the same planet (at least you couldn't in the beta).
you can fire moon to moon, right? planets no. Don't play on single orbit planets, campfest. At least till you can move moons around other moons. Then you can move your nuke battery into orbit reguardless.
Good to know, I guess next time I'll have to spam orbital fighters and the defensive unit built by orbital fabs.