"So I'm afraid we'd have to choose one or the other"<p>We could terraform Mars and turn Deimos and Phobos into a nice ring. By the time we finish, I guess we will have fast and cheap interplanetary travel, so, you could live on Mars with rings and spend your weekend on Earth, with a nice moon.<p>And while we are at it, we could also terraform Venus, increase its rate of rotation, give it a magnetic field (we would have the same problem on Mars - read <a href="http://thelazysci-fiauthor.blogspot.com/2007/04/ding.html" rel="nofollow">http://thelazysci-fiauthor.blogspot.com/2007/04/ding.html</a>). We could use repeated impacts to increase the rotation and build a ring out of the ejecta at the same time.<p>Planetary sculpture will be a hot hobby in the coming million years...