How deep has man gone in the sea? The bottom of the Challenger Deep at the southern end of the crescent-shaped Mariana Trench isn’t the sort of place people most would choose to spend their vacation. At 35,853 feet at its deepest point, it’s a cold 34oF, pitch dark, and exerts a pressure more than 1,071 times that at sea level. Yet the world’s deepest place exerts a strong pull for explorers, similar in many ways to the magnetic attraction of Mount Everest. Speaking of which, if you were to drop Everest into the Challenger Deep, its peak would be submerged by more than 1.2 miles. Undersea Exploration Methods Through History Technology has come a long way since mariners first began sounding the depths with a weighted line. And recently, OceanGate’s submarine, the Titan, has reignited discussions of the technology necessary for deep-sea exploration. Sounding weight: Essentially a sinker on a cable, this instrument has been used for centuries by sailors to chart the depths of unknown waters and avoid running aground. By the 1800s, interest in deep-sea exploration led to the development of long submarine cables. British explorer Sir James Clark Ross used a sounding weight to survey to a depth of 12,139 feet in 1840, collecting jellyfish and worms at 6,500 feet. Baille sounding machine: Similar to a sounding weight, this device included a tube that drove into the sediment on the seabed to allow the collection of specimens, including marine life. This was the main instrument used by the British laboratory ship HMS Challenger, which surveyed 68,927 nautical miles between 1872 and 1876, collected 4,700 new species of marine life, and provided the first exhaustive map of the deep ocean basins. Echo-sounding: This determines the depth of water and maps the seabed using an acoustic echo or a pulse of sound sent from the ship to the seabed and back up to the ship. Bathysphere: William Beebe and Otis Barton developed this manned steel submersible on the end of a cable that allowed them to reach a depth of 1,427 feet in 1930; 3,028 feet in 1934; and 4,495 feet in 1948. The submersible’s passengers faced the nightmarish prospect of the cable breaking and the bathysphere plunging to the depths to be crushed under pressure. Bathyscaphe: Developed by Swiss physicist Auguste Piccard, it could withstand the pressure at 4,600 feet. Auguste’s son Jacques Piccard famously used an improved bathyscaphe (Trieste) to descend with U.S. Navy Lieutenant Donald Walsh to the bottom of the Challenger Deep, reaching 35,810 feet in 1960. Manned submarines: These can take three people as deep as 11,811 feet, and come equipped with lights, cameras, and robotic arms for collecting samples. An example of these is the A\VIN Unmanned submersibles: These originally resembled steel spheres (benthographs) equipped with lights and cameras in the 1950s. Today, scientists use remote operated vehicles (ROVs) piloted via a cable connected to the ship above. Autonomous underwater vehicles (AUVs) are robotic submarines that are programmed in advance rather than piloted during the mission.