I know this may be a controversial topic to raise, but could it be that Elon's goal to very soon populate Mars is a foolish goal? My main reasons for thinking this: 1. I have never heard or read of any technological concept that would allow humans to live for extended periods of time on Mars without accumulating very high doses of ionizing radiation (due to more or less complete lack of atmosphere and the lack of magnetic field around the planet) which would make the development of cancerous tumors almost inevitable at an earlier age than on earth and in nearly 100% of the people living there. And what about children growing up, or pregnant women? I've never heard Elon touch on this subject. The only solution I could envision is living under ground for but a few hours per day, or living behind very thick walls of radiation blocking materials (which come from where???). 2. Is it really smart to contaminate the surface or Mars with earth life, before having properly explored the planet? Any biological life found on mars after a Mars lander with humans have set foot and made camp will inevitably be impossible to distinguish from contamination. This could later prove to be a huge mistake. Mars might have more value to us as a means of understanding the evolution of life, or lack thereof, on other planets. I also believe sending a manned mission to Mars would be in direct violation of the COSPAR treaty: https://en.wikipedia.org/wiki/Planetary_protection Seeing how actually establishing self sustaining life on Mars seems to realistically be very far off in to the future, would it not be better to build large space colonies closer to earth? Perhaps a proof-of-concept base on the Moon? Even if earth was hit with a very big asteroid, or if we seriously screw up the environment, our chances of surviving as a species on earth is still bigger than on Mars. If the Earth was somehow terribly messed up, our chances of being able to terraform earth back to habitability is also far greater than that of terraforming Mars, right?