> The main reason for Mars is that it is not on Earth The main reason cited is usually one of species resilience. “Not Earth” is an arbitrary requirement bolte

> The main reason for Mars is that it is not on Earth The main reason cited is usually one of species resilience. “Not Earth” is an arbitrary requirement bolted on. The main risk is that of an extinction-level event, such as large meteor impacts, substantial tectonic activity, or a worldwide nuclear disaster. All of those would likely have minimal impact on an autonomous underground city with a complete, mostly hermetic air filtering system, with three redundant power sources (say, nuclear, solar, and geothermal). That would also be substantially easier to build than a >1K self-sustaining Martian base.