1. Musk E (2014) Interviewed by Ross Andersson for the article Exodus. Aeon Magazine, 30 Sept 2014. http://www.aeon.co/magazine/technology/the-elon-musk-interview-on-mars/
2. Cf. Hender M (2009) A permanent habitat for the colonization of Mars. Masters thesis, University of Adelaide School of Mechanical Engineering, Aug 2009, in which the author makes a compelling argument for Mars being the best option. His prime reason is perhaps that the issues associated with a Mars habitat still potentially make for an easier life than that elsewhere in space, for instance on a space station, due to its similar gravity, day/night cycle, and plentiful local surface resources
3. The danger is that either by accident or design, we create a virus that destroys us. I don’t think the human race will survive the next thousand years, unless we spread into space. Roger Highfield, Colonies in space may be only hope, says Hawking. Article in The Telegraph, 16 Oct 2001. http://www.telegraph.co.uk/news/uknews/1359562/Colonies-in-space-may-be-only-hope-says-Hawking.html
4. Musk/Andersson, ibid
5. For more reasons, see Pass J, Dudley-Rowley M (2006) The cultural imperative to colonize space: an astrosociological perspective. Space 2006, San Jose, California, AIAA 2006-7488, 19–21 Sept 2006