1) A cloning mod (artifact)- can make one identical ship mod or ship artifact. example: can make a phaser if you only have one or a Thetacron Cannon with out paying it's cost. But you must have one of the artifact or ship mod to reproduce.
2)Planet destroyer- forever destroys a planet you control (100energy per size of planet) *adds (something)*
the something could be some rare artifact that was "lost" inside the planet long long ago, ctp, minerals, artifact points, or nothing
3) an artifact that can add pop to a planet like the other passive artifacts for planets
4)Other things when scanning-like black holes, nebulae, suns, asteroids, comets, ship debris and other space things... even a chance to find a whole solar system-- it's kinda odd just finding random rouge planets.
And each of those things could do different things.
For examples: Suns could add 100 energy with an 8 hour cool down time
asteroids could just contain xxxx of mining and once used disappear
nebulae- could add xxxx of research and once used disappear
ship debris- could find a "rare" mod
whole solar system-might take up 5-15 spots for planets but could add many more possibilities and reasons for doing such (leave that one open for debate)

Well you can't exactly "colonize" a star...

As for a passive population bonus, think of it realistically: Planets can have natural "attack" structures (e.g. volcanoes), defense structures (e.g. massive natural rock formations), and "cloak" (e.g. gas floating around the planet). However, a planet cannot have a natural population. The population is always changing on any colonized area; it cannot be controlled.

Your Cloning Artifact would make everything half as cheap basically.

Everything is seems pretty legit, but it would take a lot of more effort. It's multiplying a major focus of the game (planets) by like 5 to get more "planet"-like objects...

the passive pop is more like Android Helmsmans/ researchers only for the planet. if it add 5 pop per artifact... Just something new.

interesting, but probably unworkable. I do like the idea of instead of failing a scan, you find something like an asteroid or a nebula. So every time you scan but don't find a planet the game would be like "Awww, no new planet, but here, have 100 mineral points / research points / artifact points"