NASA / Reuters

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.

My personal interest in interstellar travel was piqued not by an astrophysicist, but rather by a moral philosopher. A year ago, I was having drinks with William MacAskill, a professor at Oxford University and one of the founders of the effective altruism movement. Conversations with MacAskill often turn to radical utilitarianism and audacious plans to save the world. When I asked him what he considered the most moral endeavor in the world, he said it was difficult to choose between short-term term interventions and long-term projects. For example, buying 1,000 mosquito bed nets in areas affected by malaria is almost guaranteed to save some human lives. On the other hand, giving money to an environmental lobbyist might be a terrible waste, but if that consultant persuades key members of government to lead an international effort to fight climate change, the donation could be seen as saving millions of lives.

If you spin out this logic far enough, MacAskill continued, one of the most moral projects might be to prepare for interstellar travel. After all, if the Earth becomes inhabitable—whether in 200 years or in 200,000 years—the only known civilization in the history of the solar system will suddenly go extinct. But if the human species has already spread to other planets, we will escape this permanent eradication, thus saving millions—possibly trillions—of lives that can come into existence after the demise of our first planet.

I was thrilled by this argument, yet dizzy with its implications. So, in the last episode of this season of Crazy/Genius, I sought some assistance: I asked moral philosophers, a Mars futurist, and Ellen Stofan to walk me through the colonization of Mars. What would it take? What would life on the Red Planet actually look like? And is diverting billions of dollars to interplanetary travel the most important project in human history, or an incomprehensible waste of money at a time when there are so many terrestrial crises on this side of the ozone layer?

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