I haven't read anything in this section of the site, so I don't know if this has been covered. I've read articles about terraforming Mars, and it's been said that Mars gravity, at 38% of Earth is "strong enough to hold an atmosphere". Yeah, but what if it isn't? What if a real good storm gets going, or some sort of solar event comes along, or an asteroid hits the planet? These things surely have happened on Earth with its much stronger gravity and we are still here, but on Mars, it might not turn out the same way. Might be a good thing to research a bit more before we go spending trillions fixing up the planet. No sense getting into it all if its new atmosphere can just be blown away into space one day.