The idea of humans living on Mars is closer to reality than it’s ever been. On Feb. 13, Elon Musk’s SpaceX ferried an international crew of four astronauts to the International Space Station, another sign that private companies can now routinely carry people into orbit. The company continues testing its massive Starship rocket, which it hopes will one day carry crew and cargo to the moon and Mars. NASA, meanwhile, is pressing ahead with its Artemis program , designed to return astronauts to the