I've been a forum lurker for some time now, and I have decided to make my first post. The topic of getting city lights on random planets has interested me, and I've carried out an experiment to figure out the real conditions for a planet with city lights to appear.
To begin the experiment, I started a new simulation. I placed the Sun in the center, and surrounded it with 100 random rocky planets (while on pause). All of the rocky planets were in the center of the green area in the habitable zone.
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RESULTS:After checking every planet, 7/100 had city lights. I deleted the rest of the planets without lights.
The masses of the lighted planets ranged from 0.40 Earths to 2.72 Earths.
The radii ranged from 4642km to 8125km.
The materials ranged from 2.88% iron/97.1% silicate, to 95% iron/5% silicate.
The atmospheric densities ranged from 0.715atm, to 1.99atm. Every atmosphere was bluish.
The temperatures do not seem to matter, they ranged from -34.5 to -17.8.
Curiously, none of the planets had any water. All were 0%.
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IMAGES:All 100 planets around the Sun.
http://i.imgur.com/CkRXzks.pngThe 7 planets with city lights after deleting the other planets.
http://i.imgur.com/dQoWjMW.pngA view of all 7 planets from the nightside, all with city lights.
http://i.imgur.com/Pv50We6.jpgA closeup of the city lights on one planet. They are just tiny glowing dots.
http://i.imgur.com/ubT01FZ.pngA view of all 7 waterless surfaces.
http://i.imgur.com/1XdJclP.jpg----------------------------------------------------------------------------------------------------------
Unfortunately, city lights are not persistent through saves, so saving the simulation and reloading it will remove the city lights. Deleting a lighted planet and bringing it back with Ctrl-Z will also remove city lights. Saving objects to place again will not save city lights either. Adding water will cover some/all lights, but will not remove them.
I will do more tests sooner or later, testing more conditions, such as the kind of stars required, and effects of impacts.