1) Day Night cycles aren't limited only to DX10; I've played on numerous DX9 servers on Crysis with online Day/night cycles full of people and continuously stable.
2) What kind of gaseous atmosphere does this planet have? It appears to be some kind of methane or neon, maybe yttrium (thus, the GORGEOUS purple hue)? I'm actually poking a bit in the dark here, since I'm trying to recall the descriptions of planet colors (and their corresponding gaseous compositions) from Mass Effect. I went on Wikipedia (albeit for ANOTHER particular science fiction universe; this is not actual astronomical data) just now and apparently it could probably be florescent;
http://wiki.uqm.stack.nl/List_of_planet_typesWould like to know if the devs had any planet type in mind or just liked violet

I certainly do.