CHALLENGE ACCEPTED

It’s a bright summer morning on the seemingly infinite expanse of the western Pacific Ocean, a bit over two hundred miles southeast of the island of Guam. From the deck of the DSSV Pressure Drop, nothing but the lightly rolling waters is visible as far as the eye can see in any direction—that is, except for a specific spot off the stern of the ship, where an observer might make out an unusual, curvilinear white object just slipping beneath the sparkling surface.

Though at first glance it might appear to be something out of a mid-20 ^th -century science fiction film, this object is far from an anachronism. It’s actually one of the most advanced underwater vessels ever devised, the DSV Limiting Factor. And this patch of sea, otherwise indistinguishable amidst the vastness of the Pacific, is special, too: It’s directly above—by nearly seven miles—the deepest point in all of Earth’s oceans, a notch in the Mariana Trench known as  Challenger Deep .

The Limiting Factor is the first and only vehicle to make multiple descents to Challenger Deep with human beings aboard. Prior to its initial visit to Challenger Deep in 2019, only two other human-piloted expeditions had ever made it to such depths, but on this fine day a little over three years later, the Limiting Factor is embarking on its nineteenth such dive. It’s an indication of how far deep-sea exploration has come in such a short span of time that a trek to what was once the most difficult-to-reach place on the entire planet is now starting to feel almost routine.

And yet there is nothing ordinary about this particular dive, especially not for the two blue jumpsuit-clad people who are sealed inside the submersible’s Smart Car-sized cockpit. One of them, Victor Vescovo, is responsible for maneuvering the vessel on its way to and from the bottom of the sea. It was his quest, hatched over a half-decade ago now, to personally visit the deepest point in every ocean, that led to his formation of  Caladan Oceanic , a science and technology firm dedicated to increasing humanity’s understanding of the sea. He’s piloted the Limiting Factor on 15 of its trips to Challenger Deep, but there’s a chance this may be the last time he performs that feat.

Victor’s companion on this descent is Dawn Wright. The chief scientist of Esri, the world's leading Geographic Information Systems software firm, Dawn has dedicated her life to learning about the ocean—and working to ensure that knowledge of it is made widely accessible. Needless to say, experiencing Challenger Deep first-hand would be the opportunity of a lifetime for her.

Darkness comes quickly beneath the ocean's surface. Sunlight penetrates only the uppermost 400 meters of water, a threshold the Limiting Factor blows through within minutes of sinking under the waves. The next 600 meters are fittingly called the “Twilight Zone.” It’s believed that this region is home to more marine life than the entire remainder of the ocean—and much of it provides its own radiance to make up for the lack of natural light.

As the Limiting Factor nears the lower extent of the Twilight Zone, a glow appears through Victor’s porthole, off to the sub’s left. Believing the source to be some kind of bioluminescent life form, probably jellyfish or siphonophores (a worm-like organism), Victor flashes the sub’s lights. Much to the delight of their human observers, the creatures respond in kind. This conversation of sorts between nature and machine serves as a fleeting example of the magic of the ocean. Dawn has deeply felt this magic for practically her whole life, ever since her childhood in Hawaii.

The ocean has always just been such a natural part of my life...it's a sacred place to me. When I'm in the ocean, I feel as though I am part of the ocean. —Dawn Wright

Dawn's participation in this dive is about so much more than checking an item off a personal bucket list. Her primary motivation is the pursuit of the lofty goal of mapping the entirety of the world’s oceans. Though cartographic visualizations may tempt us into thinking otherwise, only about a quarter of the seafloor has been mapped in high resolution.

On this mission, Dawn is acting as a flagbearer for three initiatives:

1.  Seabed 2030 , an international effort that aims to map every inch of the ocean by the year 2030.
2.  Map the Gaps , a non-profit that seeks to increase awareness, accessibility, and equity in ocean mapping.
3. Adding data and maps from the deepest ocean to the  ArcGIS Living Atlas of the World 's extensive collection.

Victor and Caladan are no strangers to such efforts themselves; they’ve donated over 1.5 million square kilometers of bathymetric data collected across  four years of expeditions .

And then, of course, there’s the fact of who Dawn is: She’s the first Black person and just the fifth woman ever to make the descent to Challenger Deep. She's acutely aware of the significance of that fact, and she hopes it will serve to inspire women and people of color to enter realms of science and exploration that were once all but inaccessible to them, by common practice if not by policy. Dawn is heartened, though, by the number of women who have made, and continue to make, enormous contributions to Caladan's efforts and to Dawn's dive, specifically. However, she still notes that only seven of the 43 people aboard the Pressure Drop during this expedition are women, so there's still plenty of room for improvement when it comes to encouraging and providing access to science and technology education for previously underserved groups of people.

If not for its running lights, the Limiting Factor would be engulfed in total darkness for the four-hour descent to the seafloor. The sub traverses three more vertical zones, each with an increasingly foreboding name: the Midnight Zone (down to 4,000 meters), the Abyssal Zone (to 6,000 meters), and finally, the Hadal Zone, occupying anything below that. This is the most tedious part of the adventure, but fortunately, there’s plenty to talk about. Some of it critical to the mission, such as making sure Dawn is familiar with the basic controls of the Limiting Factor in the unlikely event that Victor should become incapacitated.

Dawn is well versed in submersibles, having done her PhD work studying mid-ocean ridges, so she's able to approach a dive of this magnitude like she would any other, as a professional. Perhaps as a result of that mental approach, Dawn barely notices when the Limiting Factor floats past the 2,500 meter mark, making this now the deepest she has ever been.

The major difference in preparation compared to her shallower dives was a fasting regimen, given that there's no latrine aboard the Limiting Factor. The round trip to and from Challenger Deep can often take a half day or more, so Dawn had to reduce her food consumption over two days, with a final snack and sip of water a few hours prior to launch.

Apart from that, there is little difference about the process of the descent itself from a sensory standpoint. If anything, it’s actually more comfortable than her past experiences, given the length of the dives the Limiting Factor has been designed for. Even the pressure outside the sub, increasing to almost unimaginable levels, is imperceptible to the occupants of the Limiting Factor. At the full depth of Challenger Deep, it’s as though there’s a school bus sitting on top of every cubic inch of water, but Dawn and Victor, protected inside the meticulously engineered chamber of the sub, would never know that.

Some of Dawn and Victor’s traveling companions, however, are less safe from the effects of the deepest sea. A handful of Styrofoam cups, each bearing colorful doodles, remain just outside the hatch of the Limiting Factor in a mesh bag. As the sub descends, the cups are fully exposed to the crushing water pressure. When the sub returns to the surface, the cups are retrieved—badly warped and a fraction of their original size, but, amazingly, mostly intact.

The expedition's symbolic importance aside, Dawn's dive has an immediate, tangible goal: pushing the science of seafloor data collection to new limits.

Multibeam sonar systems, such as the one affixed to the bottom of the Pressure Drop, are effective for capturing the bathymetry (depth data) of large swaths of the ocean floor. Portable sidescan sonar systems, on the other hand, are frequently used to produce more detailed images of the seafloor. These sidescan devices are often deployed closer to the seafloor and can thus more accurately read differences in material and texture by measuring the intensity of the return signals, rather than merely the time it takes for the signal to bounce back. This makes sidescan particularly effective for purposes such as finding shipwrecks, determining the state of underwater infrastructure, or locating mineral deposits.

Portable sidescan sonar, though, has never been deployed deeper than 6,800 meters; its circuitry generally doesn’t hold up well against the immense pressure of the deepest sea. But now, a Mauritius-based company called  Deep Ocean Search  has recently developed a sidescan sonar apparatus that is designed to withstand the pressure and work at full ocean depth. Victor and Dawn have arranged for this new device to be attached to the outer shell of the Limiting Factor; if it functions successfully in Challenger Deep, it will represent a game-changer in the field of seafloor mapping.

At about 10,450 meters, still roughly half a kilometer above the floor of the trench, the moment of truth arrives. Cradling a laptop computer in her lap, Dawn powers up the sidescan for the first time. Much to her relief, the sonar’s signals are reading clearly.

There’s hardly time to celebrate the success of the sidescan’s operation before the bottom of Challenger Deep is upon Dawn and Victor. As the seafloor rises up to meet the Limiting Factor, they are greeted by an unusual, green, cylindrical object. As they get closer to the object, they realize that it’s no natural formation.

“It’s a freaking bottle,” Victor remarks, with some trace of disgust. He’s seen evidence of human life down here before—mainly gnarled cables, presumably left behind by previous deployments of scientific vehicles—but it never fails to serve as a sobering reminder that human activity is impacting every corner of the globe.

For Dawn, at least, the disappointment of stumbling upon the bottle is quickly replaced by a more positive emotion—elation. She's made it to the deepest point in the world, after all.

The mid-ocean ridges are very active, very exciting...Challenger Deep is not like that—it's a barren, forbidding landscape. But it's Challenger Deep! At the same time, that's extremely exciting, too. —Dawn Wright

Within a few minutes, the Limiting Factor reaches its maxmium depth for this expedition: 10,919 meters. Dawn and Victor take note of some holothurians (sea cucumbers) nestled on the seabed. It’s something of an antidote to the bottle episode; there’s a certain comfort in the realization that forms of life have been surviving even in these most inhospitable places since long before our species evolved, and they’ll likely continue to exist long after we’re gone.

Challenger Deep contains three distinct “pools” within it that drop below that magic 10,900 meter mark. The absolute deepest points are located in the Eastern Pool, which has been the destination for most of the Limiting Factor’s descents. On this dive, though, Victor and Dawn are targeting the relatively unexplored Western Pool. In fact, their planned sidescan survey route will take them through completely new territory; they will be the first people ever to set eyes on the ground they’re about to cover.

Their track takes them along the floor of the Western Pool and then gradually climbs the “wall” of the trench. All the while, the sidescan pings away. Though the data it’s obtaining may not amount to a major scientific breakthrough, its continued operation in this environment is a massive victory.

At any rate, the most interesting observations are made visually by Dawn and Victor. Dawn is able to witness first-hand the results of geologic processes she has made a career out of studying. For instance, fields of angular, blocky boulders have been left in the wake of tectonic plates that have been colliding over millions of years. She christens one particularly impressive outcropping "Flintstone's Quarry."

After nearly two and a half hours exploring Challenger Deep’s Western Pool, the time has come to begin the ascent back to the surface. For all of the Limiting Factor’s technological wizardry, this process simply involves discarding several metal weights. (“They’ll dissolve at this depth,” Dawn points out, to comfort those of us still fretting about that errant bottle.)

With the sub now appreciably less heavy, the return journey is about an hour shorter than the descent. Now is the time to decompress, both literally and figuratively. Victor’s smartphone comes in handy here, as he's downloaded a couple of pre-selected movies onto it.

Dawn’s pick is “Star Wars Episode 1: The Phantom Menace.” It might seem a curious choice, at least until she cites the memorable scene that takes place in an underwater vehicle. Then there’s still enough time left for Victor to run through some hand-picked scenes from “The Life Aquatic with Steve Zissou.” Before Dawn knows it, the water outside the viewports starts to take on a lighter gradient. At last, after exactly ten hours beneath the waves, the Limiting Factor bobs serenely to the surface.

There’s still plenty of daylight when the Limiting Factor peeks above the water, though the sun has migrated most of the way across the watercolor sky. A man in a fluorescent yellow vest dives into the ocean from a Zodiac raft and swims over to manually attach a tow cable to the submersible so that it can be brought back aboard the Pressure Drop. His name is Shane, but he’s affectionately known as “Speedo.”

Speedo’s duty, as straightforward as it seems, represents just one of many crucial roles that have enabled Caladan’s missions over the past half-decade. These range from the engineers and technicians responsible for the ground-breaking technology used throughout these expeditions, to the cartographers and scientists who are able to contextualize discoveries, to the crew that keeps the Pressure Drop running, even including the on-ship cooks.

Upon being pulled from the Limiting Factor, exhausted but still running on adrenaline, Dawn is more than ready for a hot meal prepared by those cooks. She has to keep her game face on a little longer to indulge the media crew that’s there to document her achievement, but soon she’s able to join Victor in the galley for a plate of spaghetti and meat sauce. It’s past dinner hour for the rest of the ship, so they’re able to share a quiet moment together in reflection.

For Victor, it’s possible that this is the final time he’ll ever pilot the Limiting Factor to the bottom of Challenger Deep, which makes the moment especially poignant. Since the start, he’s largely financed Caladan and its operations out of his own pocket, with the occasional infusion from “trench tourists” who are able to pay a hefty fee to visit the deepest point on Earth. Now, though, he has found a buyer for the whole Hadal Exploration System—including the sub, the ship, and all the trimmings, which leaves him looking for his next adventure.

For Dawn, the work continues. Where once the mysteries of the deep sea were met with a collective shrug by the general public save for the alien-like creatures that can be found there, there’s now a growing understanding of the practical benefits of the knowledge that these discoveries can provide.

Undersea infrastructure, for example, already has a massive, invisible hand in our everyday life in this era of ever-increasing globalization. Fiberoptic cables enable communication from one end of the earth to the other, while pipelines conveying oil and gas power our cities. Naturally, such critical foundations of the functioning of our society also carry enormous national security implications. Without expertise on the bottom of the sea, it isn't possible to know where all of this infrastructure is, where more can be added, and what might pose a threat to it.

Then, of course, there's the question of resource extraction. While Dawn acknowledges that deep-sea mining will likely be a going concern in the not too distant future, it will be all the more crucial that there are people who are positioned to ensure such activities are carried out responsibly.

It will be people like Dawn—possibly even those she's directly inspired—who are vital to maximizing the potential of the human race as we navigate an uncertain future together.