The deepest place in the World Ocean is 35,840 feet (nearly seven miles). This is the Challenger Deep in the Mariana Trench, about 200 miles southwest of the Pacific island of Guam. It was here in January 1960 that the U.S. Navy's bathyscaph Trieste dove to 35,800 feet.
Thirty-four years later, the unmanned Kaiko, Japan's newest remotely operated vehicle, returned to the site. It missed equaling the Trieste's record by only 14 feet. Since then, the Kaiko has made two other expeditions to this area but has not exceeded the manned record.
No human has returned to the deepest place in the sea since the two-man Navy team was there 42 years ago. Mount Everest, the highest place on our planet, has been climbed by more than 1,000 adventurers, and about the same number of astronauts have been in space. The moon's surface has been visited six times, and there is talk of a future manned mission to Mars. Yet, the greatest ocean depths on Earth are not accessible to manned inner spacecraft.
The topography of the global seafloor is hardly a flat-bottom plain. A world-girdling mid-ocean ridge system stretches for some 40,000 miles, the greatest mountain chain in the world. Extensive canyon systems or trenches, most miles deep, are carved into the seafloor. The greatest number are in the Pacific, but they also are found in the Atlantic, Indian, and Southem Oceans. Very few trenches have been investigated with either manned or unmanned submersibles.
After her 1960 dive, the Trieste was modified to go no deeper than 20,000 feet. The French Navy's bathyscaph Archimede, retired in 1977, was the last manned submersible capable of maximum depth. It has been a quarter of a century since a manned submersible has been capable of depths greater than 22,000 feet.
Why did this maximum-depth capability go away? It is not the old question of manned versus unmanned; manned submersibles are used regularly today for oceanographic research. Worldwide, at least a dozen are dedicated to this work. It is more likely a matter of economics—97% of the seafloor is accessible if you can dive to 20,000 feet. For engineers, bean counters, and policymakers, this is good enough.
The remaining 3% of the seafloor, however, represents an area equal to the entire United States (including Alaska and Hawaii) plus about half of Mexico. Imagine a chunk of land this large remaining unexplored.
The Navy's last bathyscaph, the Trieste II, was retired in 1982 and replaced by the modified Sea Cliff, which had been upgraded from a 6,000- to a 20,000-foot capability. Shortly thereafter, the French launched the Nautile. By the end of the 1980s, three more 20,000-foot submersibles had joined the club: two Soviet Mir vehicles built in Finland and Japan's Shinkai 6500 (now the world's deepest diving submersible, at 6,500 meters or 21,325 feet).
Four of the five still are operating (the Sea Cliff was retired four years ago without a replacement). The United States might not be out of the club for long, however. The National Science Foundation and National Oceanic and Atmospheric Administration have funded a serious study for a new manned submersible. A committee based at the Woods Hole Oceanographic Institution is developing a conceptual design for a 6,500-meter replacement for the venerable Alvin (13,500 feet). The group believes this capability can be achieved without significant technological or logistical problems. The preliminary cost estimate for this new vehicle is about $25 million.
Man must access, explore, and study all places on the planet Earth. In the deep oceans this capability has been missing since 1977. A single maximum-depth submersible, with a dedicated mother ship, is needed to investigate global ocean trench systems. This could be an international "inner space station," available to scientists of all nations. The United States is the most qualified sponsor of this initiative. With a 6,500-meter Alvin replacement likely, an 11,000meter manned submersible system would be a logical follow on. Compared to costs of space exploration, the national investment in this underwater system would be quite modest.