Into the deepest blue

A diver films the deep-sea explorer Nereus from the water during its second expedition in 2009 to investigate hydrothermal vents along Earth’s deepest mid-ocean ridge in the Cayman Trough. On May 31, 2009, the robotic vehicle successfully reached the deepest part of the world’s ocean — the Challenger Deep in the Mariana Trench in the western Pacific Ocean.

(Photo courtesy of Advanced Imaging and Visualization Laboratory, Woods Hole Oceanographic Institution)