the current patch has brought in a new idea, search based planet bonuses. currently there are a few (and they arent bad, I like porous core!) but theres no harm in throwing together some ideas for the devs. so here are a few of my own

Heavy Metal Core (d): opposite of porous core, a bigger gravity well
Thin Atmosphere (d): resistant to being nuked, but lower populace limit
Strong Ionosphere (d): propoganda takes longer to expand near planet, decays more rapidly
Intelligent Populace (s): functions as an extra military or civilian lab
(if there are gas giants) Protostar (d): hard to detect entering/exiting gas giant's gravity well
Hydrocarbon Atmosphere (d): increase in exports, prone to nuking
Pirate Base (d): increase in trade, greater populace limit, much greater infrastructure health
Hostile Conditions (d): slightly lower populace limit
Crystal Deposits (s): slow to mine, but infinite source of crystal found within planet
Metal Deposits (s): slow to mine, but infinite source of metal found within planet.

(s) : indicates found upon search
(d) : indicates known upon discovery of planet

obviously the benefits cant be too powerful (explods upon culture switch!)