It’s the risk that comes with exploring the unknown: Saturday afternoon, 6 miles under the sea, a remote-controlled robot probing one of the coldest, deepest ocean trenches on Earth blew apart.
The one-of-a-kind Nereus, built by Woods Hole Oceanographic Institution, had just embarked on a three-year project to explore deep-sea ecosystems and the weird, unknown critters that inhabit the ocean’s most remote trenches. Researchers said the loss of the $8 million sub is a huge disappointment for the expedition’s scientists and a major setback for ocean science, with a next-generation rover capable of probing such depths still in the design stages.
“Without Nereus, we currently have nothing that will enable us to reach that part of the ocean,” said Larry Madin, director of research at Woods Hole.
Scientists still don’t know exactly what happened to Nereus at the Kermadec Trench, the fifth-deepest ocean trench, which is off the coast of New Zealand. But they have a good guess: 6.2 miles below the surface, pressures 1,000 times greater than the ones at sea level probably led to the implosion of one of Nereus’s pressure housings, chambers that protect sensitive electronics and other gear from the extreme pressures. The force would have set off a chain reaction, causing the submarine to fail. Bits of debris from the robot have been recovered at the surface.
“It’s an ever-present risk,” Madin said. “The way things go down there, everything’s operating normally and suddenly everything goes dark, and when it’s 6 miles down in the ocean, you don’t have a good way of knowing what’s happened — you can only make inferences based on what you know of the system and the forces that could be acting on it.”
The failure certainly wasn’t anticipated: Nereus, launched in 2008, is one of only four underwater vehicles to have ever visited an even deeper spot in the ocean — the Challenger Deep, which is 6.9 miles below the surface at the Mariana Trench. Brian Midson, of the Submersible Support Program at the National Science Foundation, which funded most of the project, said parts of Nereus had been pressure-tested at twice the pressures it experienced.
But seven hours into a nine-hour exploration and three-quarters through the robot’s 40-day expedition, the scientific team on the ship lost contact with Nereus.
“This is a tight community,” said Midson, who learned of the failure in a late night phone call. “It affects people’s research, careers, employment. It has deeply felt impacts for the community and the operators.”
The robot was a key part of the Hadal Ecosystem Studies Project, a federally sponsored effort to systematically study life deep in ocean trenches. The extremes of the deep ocean, including intense pressures and uninterrupted darkness, have become an area of scientific interest because understanding the ecosystems that have evolved in such environments might provide insight into how life emerged on Earth.
“We’re always interested in where and how life survives on the planet. This is really the last frontier of exploration,” Midson said. “You may hear about how underexplored the oceans are, and this would be the least explored of the underexplored parts.”
Now, the future of that program is in question. Scientists are still out at sea collecting the data they can with other instruments, but Midson said that when they return, project directors will need to decide how to move forward without their most valuable tool.
The underwater explorer incorporated novel engineering features that were seen as major improvements over previous robots. It was powered by more than 4,000 lithium-ion batteries, allowing it to forego a heavy and long power cord that had limited the range of previous deep-sea rovers and required a much larger ship as a launch platform.
Using a mechanical arm, it could take samples that could be returned to the surface, as well as video and photos. Nereus was also able to operate autonomously or by remote control, tethered only by a fiber-optic cable.
Midson said it was difficult to estimate the typical life span of a roving undersea vehicle. The manned submarine Alvin has been in use for nearly 50 years. In 2010, an unmanned robotic vehicle called ABE was lost at sea, probably due to a similar implosion. But the legacy of Nereus may be the discoveries it made on dives right before it failed.
Nereus had collected sediment samples, biological specimens, and images that appear to represent previously unknown species — the discoveries are so new, Madin said, that the scientists are not yet sure what to make of them.
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