Mars is spelled with capital 'M'

also is not preceeded with 'the'.
Same would apply to Earth, Saturn, etc.
But not 'the moon', 'the asteroids'.
There are various known moons, asteroids, suns/stars -> preceded with
'the' and lower-case.
There is only one Earth, Saturn, Pluto etc. -> no 'the' and capitalized.

privs/layers.lua

@@ -12,7 +12,7 @@ minetest.register_privilege("asteroids_access", {
 })
 
 minetest.register_privilege("mars_access", {
-	description = "Can travel to the mars",
+	description = "Can travel to Mars",
 	otp_keep = true
 })
 

travel/travel.lua

@@ -22,7 +22,7 @@ pandorabox.can_travel = function(player, pos)
 
 	-- mars
 	if pos.y > 10000 and pos.y < 17000 and not minetest.check_player_privs(player, "mars_access") then
-		return false, "You need the 'mars_access' priv to go to the mars!"
+		return false, "You need the 'mars_access' priv to go to Mars!"
 	end
 
 	-- warzone