Image: Remarkably, there is no definite measurement for the Challenger Deep, the deepest part of the Mariana Trench. Measurements taken from the surface using sonar are calculated using the speed of sound traveling through water—but that speed varies depending on the water’s temperature and salinity. The best sonar reading to date, taken in 2011, put the trench’s lowest point at 10 994 meters.
As the battered little boat slides down a 3-meter ocean swell into the next trough, Chris Welsh grits his teeth and peers out into the storm. Sheets of rain pummel the dark windows of the bridge, and a Micronesian sailor wrestles with the wheel. It’s past midnight on a July night and we’re bobbing over the almost 11 kilometers of water that fill the deepest abyss on Earth, the Mariana Trench. Welsh is leading a small party of engineers, scientists, and adventurers under the banner of Virgin Oceanic; they’ve chugged out here aboard a 20-year-old ferryboat to test some unmanned deep-diving probes. It’s the first step in what they hope will be a glorious high-tech adventure, in which a man—Welsh, specifically—will visit the bottom of the trench before the end of this year.
But right now, most of us would be happy just to make it back to Guam, 130 km (81 miles) to the north. Another wave breaks over the boat and crashes down on the cabin house, dousing the upper deck. I recall a plaque mounted on a table in the main cabin that admonishes, “No passengers more than 20 miles from shore.” This 20-meter-long vessel is what oceanographers call a “ship of opportunity,” which means it was pressed into service for the mission basically because it was available. Welsh turns to the captain, who lives in the Mariana Islands, and asks, “In your experience, what usually happens in a storm like this? Does it get better? Does it get worse?”
The captain keeps the boat’s prow pointed firmly into the waves. “I don’t know,” he says. “I’ve never seen it like this.” It occurs to me that if the boat sinks, it will take 3 hours to reach the seafloor.
Of course, it wouldn’t be real adventure if there wasn’t any danger. Like the South Pole, the peak of Mount Everest, and the moon, the Mariana Trench is a singular place that looms large in the human psyche. Countless ordinary people have imagined what it would be like to be there, and a very few extraordinary people have actually managed to go. Of all those singular places, the bottom of the Mariana Trench has had the fewest visitors—precisely two. In 1960, U.S. Navy lieutenant Don Walsh and Swiss engineer Jacques Piccard rode down in a primitive vehicle called a bathyscaphe (essentially a small metal sphere attached to an enormous bag of buoyant gasoline). No one has been there since, although three unmanned vehicles took the plunge in the 1990s and 2000s.
If Walsh and Piccard’s bathyscaphe was a dirigible, the sleek experimental vehicle being built for Welsh is a fighter jet. Welsh plans to pilot it on the world’s first solo dive to the trench bottom. He’ll be accompanied by an entourage of robotic landers, the prototype of which we’re now testing in this stormy sea. We dropped the lander 6 hours ago, and by now it has completed its round trip to the seafloor and is bobbing somewhere out there on the dark waves. The researchers on board dearly want it back, with its payload of deep-sea water samples. But the radio beacon attached to the probe isn’t sending out its location signal, and there’s no sign of the instrument’s flashing strobe light in the storm. If an unmanned probe carrying only electronics can run into this much trouble in the Mariana Trench, what difficulties will confront the actual sub, with its cargo of human life? …