To understand why genetic engineering is the only way humanity can conquer Mars and the rest of the solar system, consider what the current version of Homo sapiens will have to endure on a trip to the Red Planet. Any crew dispatched on the 18-to-30-month mission to Mars will face highly elevated risks of cancer, tissue degradation, bone density loss, brain damage, pharmaceutical spoilage, and other health threats. The journey outside Earth's magnetic field will expose astronauts to solar flares and cosmic radiation at levels that have not been surveyed since the end of the Apollo missions (the longest of which lasted just 12 days). Arrival on Mars, a geologically inert body with one one-hundredth of Earth's atmosphere and no shielding from solar radiation, will provide little relief and will probably introduce some secondary radiation risk from solar rays reflected off the Martian surface. Still, writes Tim Cavanaugh, the romance of sitting on Mars is pretty powerful, and leading space entrepreneurs want to make it happen.