Unmanned Sub Dives the Marianas Trench on a Hair-Thin Tether

Nereus becomes the third craft to explore the bottom of the Marianas Trench

On May 31, the unmanned submersible Nereus became only the third craft ever to reach the full depth of the Marianas Trench, 35,770 feet below sea level. Built by the Woods Hole Oceanographic Institution, the sub is a hybrid of a remotely operated vehicle (ROV) and autonomous underwater vehicle (AUV). The Nereus runs on its own battery power, but researchers on a mother ship send it commands over a single hair-thin fiber-optic line that’s 25 miles long but weighs just 1.35 pounds.

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