Mars is a floating ball of rock sitting in the orbit of the Sun. The only difference between this lump of floating rock and the other lumps of floating rock in our Solar System is the fact that this one is red. This instantly makes it more well known and more likely to be used in science fiction than any other planet. Mars is the home planet of a bunch of reptilian warrior creatures known as the
Silurians Ice Warriors, polluted water than turns people into zombies, and... no, that's pretty much it. Is anyone really surprised that there are two main aliens on Mars though? I mean, look at it, it's a lump of floating rock, it doesn't even have anything else on it, it's literally rock. That's the most boring thing a planet can be. Mars has made several appearances in Doctor Who before, but I'll be damned if I'm going to list them all here. Go and research it yourself mate.
Oh yeah, and apparently some English soldiers get stuck there in Series 10 and have to fight Ice Warriors. I don't know, they episode hasn't aired yet.