I am not natively English speaking and I was wondering about this spelling when I saw the title of the movie "The Martian".
This pattern also seems to apply to other things ending on an "s" sound, like
- Venus -> Venutian (though it's less common than Venusian)
- Venice -> Venetian
On the other hand, there is examples showing the exact opposite, like
- Paris -> Parisian
- France -> French
- Los Angeles -> Angeleno (probably derived from its hispanic origin)
Why is it not "Marsian" and "Venecian" like it is in German for instance ("Marsianer", "Venezianer")?
Is there a rule for how demonyms are spelled or do they evolve historically?