Donkey Kong Country: Tropical Freeze is all about snow; that much should be obvious from the game's title, even for those who have yet to play Retro Studios' excellent platformer.
According to a recent interview from KiwiTalkz in which he chats with former Retro artists Eric Kozlowsky and Ted Anderson, however, early development included a potential martian theme for the game. This was only briefly considered, as the studio was pretty set on the Snowmad enemies at the time, but the gist would be that aliens living on the moon would invade Donkey Kong Island after DK punched it at the end of Returns.
Very few pieces of concept art were produced for the idea, and Kozlowsky and Anderson describe the whole experiment as "superfluous" in terms of its overall impact on development, but it's certainly an interesting glimpse into what could have been had the studio decided to run with it.
The direct quote, which can be found at 50:41 in the above video, reads:
"I think early on, I think it might have been discussed like were we going to do the snow theme or like a martian theme where because DK punched the moon at the end of returns, the aliens living on the moon were going to be the invaders."
All told, we're pretty thrilled with what we eventually got with Tropical Freeze, but if Nintendo wants to bring back the martian theme for a potential future title, we'd be all for it.