Of course, Cousteau comes from a family of aquaphiles. His father Jean-Michel, his sister Céline, and cousins Philippe and Alexandra have all dedicated their lives to ocean exploration and advocacy. His famous grandfather Jacques-Yves Cousteau believed that one day humans would build and inhabit underwater cities. He built the first underwater habitat, called Conshelf I (short for "Continental Shelf Station"), in 1962. Then came Conshelf II and Conshelf III. Jacques made history by spending 30 days under the Red Sea aboard Conshelf II. Fabien Cousteau will, if all goes well, break his grandfather's record by one day—and by several meters. For the rest of us, the biggest difference this time around is that the entire adventure is being broadcast live. Cousteau has been telling reporters to think of the mission like "an underwater Truman Show."

He and his fellow aquanauts will communicate with the reporters and science teachers and students around the world every day via email and Skype. They plan to spend hours each day outside Aquarius, taking rocket-pack-assisted swims around the habitat and roving the continental shelf on motorbikes.

There is, of course, much to explore. Ocean scientists have made enormous strides in underwater research, but the 20th century's love affair with outer space means we know far more about the moon than we do about the sea floor. Cousteau sees Earth as a "little brown veneer," compared with the vastness of the sea—and he gets frustrated when people marvel at the Earth's oceans by saying that 70 percent of the planet is covered by water.

"[That's] talking about the world in a two-dimensional way, and the planet is three-dimensional," he said. "So if you’re talking about a three-dimensional system, the oceans represent 99 percent of our world's living space. And yet we’ve explored less than 5 percent of it."

This is something of a sore subject for ocean scientists, who point out that public funding for space exploration dwarfs the money that undersea researchers get. The United States government spends over 100 times more on space exploration than ocean exploration. Astronauts outnumber aquanauts by a similarly huge factor. But, Cousteau argues, the ocean has as much to do with the future of mankind as Mars does. "Space exploration is equally important, but if we don’t take care and understand our life support system first and foremost, then how can we imagine going beyond this little planet which sustains all life that we know?" (Or, as submarine designer Graham Hawkes puts it: "Your rockets are pointed in the wrong goddamn direction!")

Mission 31 is concerned with how the oceans are changing—namely, what we humans are doing to them. We've been using them as a carbon sink, a garbage dump, and simultaneously, a garden from which to harvest. Three broad subjects of study for the Mission 31 scientists are ocean acidification (as it relates to climate change), ocean pollution (with an emphasis on the effects of plastics), and declining biodiversity (attributed to overfishing). This is a bona fide research expedition, but it's also a publicity stunt. Cousteau wants to drum up enthusiasm for the sea, which helps explain why he's letting celebrities like rapper will.i.am and billionaire entrepreneur Richard Branson dive down to Aquarius for short 45-minute visits, and auctioning off similar experiences to the highest bidders. The idea, Cousteau says, is to spark the interest of a population of people who haven't previously gotten excited about the ocean—and to change the way they think about the planet.