Nereus carried out missions in the deepest parts of the oceans, where pressure can be as great as 16,000 pounds per square inch.

WHOI Advanced Imaging and Visualization Lab

Ocean researchers are mourning one of the most advanced craft they could use to probe the mysteries of the deep, with the loss over the weekend of Nereus.

Operated by the Woods Hole Oceanographic Institution (WHOI) in Massachusetts, Nereus could either be controlled remotely by scientists as it descended thousands of metres into the sea, or it could be dispatched to autonomously swim the depths.

On 10 May the unmanned vehicle was exploring the Kermadec Trench off New Zealand when it was lost 9,990 metres under water. Staff on the ship Thomas G. Thompson, which was operating Nereus, later recovered debris from the submersible floating on the surface. It is possible that one of the ceramic spheres that gave the craft buoyancy imploded under the pressure of thousands of metres of water.

“Nereus helped us explore places we’ve never seen before and ask questions we never thought to ask,” said WHOI biologist Timothy Shank in a statement.

Nereus cost more than US$8 million to build, and had been in operation since its first sea trials in 2009.

“It was a one-of-a-kind vehicle that even during its brief life. It brought us amazing insights into the unexplored deep ocean, addressing some of the most fundamental scientific problems of our time about life on Earth,” said Shank.