ONE OF only four submersible vehicles in history to reach the deepest part of the ocean in the Marianas Trench, the remotely operated vehicle (ROV) Nereus, has been lost at sea while exploring the Kermadec Trench, northeast of New Zealand.

The ROV was confirmed lost at a depth of 9,990 metres, the Woods Hole Oceanographic Institution (WHOI) wrote in May, with scientists saying a portion of the vessel likely imploded under pressure as great at 16,000 psi.

At the time it was lost, it was 30 days into a 40-day expedition on board the research vessel Thomas G. Thompson to carry out the first-ever, systematic study of a deep-ocean trench as part of the US National Science Foundation-sponsored Hadal Ecosystems Study (HADES) project.

Researchers on the Thompson lost contact with the vehicle seven hours into a planned nine-hour dive at the deepest extent of the trench.

The researchers spotted debris from the Nereus during a search near the dive site, saying initial indications suggested a catastrophic implosion of the vehicle.

Built in 2008 by the Deep Submergence Lab at WHOI with primary funding from the NSF, the ROV could descend to the deepest parts of the ocean and operate either autonomously or be controlled remotely from the surface.

Nereus WHOI engineers incorporated a number of novel technologies into its design for use in remote operations, including an optical fiber tether for use in remote operations, ceramic flotation, and lithium-ion batteries.

NSF chief scientist Timothy Shank said the Nereus helped researchers explore places never before seen.

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

The vessel had been scheduled to return to the Mariana Trench in November as part of the second HADES expedition.

It had previously explored the world’s deepest known hydrothermal vents along the Cayman Rise in the Caribbean Sea.

On the first HADES cruise, Nereus had brought back to the surface specimens of animals previously unknown to science and seafloor sediment destined to help reveal the physical, chemical, and biological processes that shape the deep-ocean ecosystems in ocean trenches, which are unlike almost any others on the planet, WHOI said.