Fresh from becoming the first private US company to deliver cargo to the International Space Station, the billionaire founder and CEO of SpaceX, Elon Musk, is now eyeing even further afield. According to Space.com, he's been speaking about his plans to start-up a colony (of around 80,000 people) on Mars in the not-too-distant future, with tickets to the planet likely to cost around half a million dollars each.