I've forgotten most of my Earth Science knowledge, but to keep a "realistic" feel on the science-fiction project I have I need to create a realistic planet. My imagination of the planet is a frigid and barren land, yet inhabited by creatures that can survive its temperatures. The problem is humans, who will come into contact with the alien species. Giving room for technological advancement, what do you think the coldest temperatures are that a human (with proper space gear on) could survive on another planet? And how far from a sun-sized star would this planet be? Another question: Is it possible (realistically) for a planet to be in permanent darkness, or at least semi-permanent (3/4 of the day)?