As an incubator of life, Earth has a lot going for it, something we often fail to appreciate fully from within its nurturing bounds. Merely sending probes and rovers to the moon and Mars won’t do. For various reasons — adventure! apocalypse! commerce! — we insist upon taking our corporeal selves off-world too. Multiple private companies have announced plans to put hotels in space soon. NASA is aiming to 3-D-print lunar neighborhoods within a couple of decades. And while it will probably take longer than that to build and populate an outpost on Mars, preparations are being made: This summer, four NASA crew members began a 378-day stay in simulated Martian housing at the Johnson Space Center in Houston. Here’s some of what we know about how Earthlings fare beyond the safety of our home world.