A computer on Mars doesn't need a whole different operating system. It just needs a different calendar and clock. Cory Doctorow wrote in his story Martian Chronicles about how computers needed to run on a Mars-specific operating system, to match the particular clock and calendar for that planet. It may also have been a point about the specific circumstances of that story, but it shouldn't really matter. You can run a different clock and calendar on the same operating system as everyone else. The computer doesn't mind, as long as there's a way to translate dates to and from a number of milliseconds. That's all it would need.
Mokalus of Borg
PS - This is one of those technical discussions that bugs me, deep down.
PPS - It's also one of those with very little impact on my life.