The Earth and Mars are a bit like fraternal twins that slowly grew apart. Four billion years ago, both planets were warm, sheathed by protective atmospheres, and carved with rivers and pools of liquid water. But today, Mars is an irradiated desert enveloped by a thick miasma of carbon dioxide, while its twin is a sensationally fertile orb and, for all we know, the universe’s cosmic jackpot of life.
These divergent stories make scientists immensely curious: Can we discover evidence of a fecund past in the Martian ground? We’re closer than ever to finding out. Ellen Stofan, the former chief scientist of NASA and current head of the National Air and Space Museum, has predicted that we will find evidence of past life on Mars in as little as a decade.
Others have more audacious goals. They see Mars not just as a planetary mausoleum of dead microbes, but as humankind’s next planetary home. Some time in the future, they point out, the Earth will be uninhabitable, whether due to climbing temperatures, rising seas, global nuclear war, an inauspiciously precise comet, or the inevitable transformation of our sun into a planet-swallowing red giant. Scientists and aeronautical engineers are already preparing for this cataclysm by building ever larger rockets and setting up simulations of human life on Mars on a Hawaiian volcano, with uneven results.