all ideas are great. but for simplified coding make each planet have just 1 environment. but the day/night cycle works only for planets with oxygen. BUT with a space suit that doesn't matter.
what it should be done is make the temperature aside from any effect of the planet. and base the temperature hazard according to the distance from the star. you dont see pluto getting hot on the sunny side, its cold everywhere, just as mercury is almost always too hot.
this also should depend on the type of atmosphere, gaseous ones should retain the heat, and planets without much should be cold most of the time.
what i'd like:
damage for entering the atmosphere (depending on what type is) and get shield damage and after some hull damage.
make the atmosphere BIGGER so the time "burning" your entering shields is greater than just a second if your fast enough, talking of fast it should also change upon the velocity youre going into the atmosphere.
also it would be impossible to enter planets with considerate atmosphere on "foot"
render space mining null for ships too small in scale of the planet, so only bigger ships can actually mine from space. so as many said, give smaller ships that enter the planet value to mine inside, but they cant just enter with the core and start mining there, it should have a block threshold i.e. a too small mass ship on a too high atmosphere should destroy the ship and kill you, so you have to pick which planet you want to enter, this will also make planets good hiddings pots and good for HQs.
i have alot of more ideas but im tired and need to lay down. also apologizes if i couldn't transmit the idea how i wanted