Six Miles of Ocean Imploded a Robot Submarine

Twenty days into a 30-day mission, seven hours into a nine-hour deep dive, scientists aboard the Thomas G. Thompson research ship the lost contact with their remotely operated robotic submarine.

The unmanned vehicle, Nereus, was exploring the Karmadec Trench northeast of New Zealand, going as deep as 11,000 meters—almost seven miles below the surface. After emergency recovery protocols failed to bring Nereus back, the scientists began searching near the dive site. From the Thompson, the scientists spotted debris floating on the surface. It was from Nereus. At 2PM Saturday, the robo-sub was confirmed as lost.

"Nereus helped us explore places we've never seen before and ask questions we never thought to ask," said the mission's chief scientist Timothy Shank, a biologist from Woods Hole Oceanographic Institution (WHOI) in a press release about the missing sub. "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."

The WHOI is a leader in the development of autonomous robotic vehicles for exploring the ocean. The BBC's Jonathan Amos called Nereus “a flagship ocean explorer for the US science community.”

It was a hybrid vehicle that could work as either a remotely operated vehicle via an optical fiber tether or as a free-swimming autonomous vehicle. Built in 2008 for $8 million, it was one of only four submersibles in history to reach the deepest part of the ocean in the Challenger Deep of the Marianas Trench, which it did on its first mission in June 2009.

The scientists are still collecting as much debris as they can find to better understand what happened to Nereus. It was lost at 9,990 meters, or 6.2 miles down, where the pressure can be as great as 16,000 pounds per square inch. They believe that Nereus was felled by a “catastrophic implosion.”

But most are taking this opportunity to remember the good times. Why, it seems like it was just the other day when Nereus was successfully coming up from a 6.8 miles-deep dive with sediment it collected from the bottom of the Marianas Trench with its robo-arm. Andy Bowen, project manager and the sub's principle developer at WHOI, sounded so proud as he told the BBC, “With a robot like Nereus, we can now explore virtually anywhere in the ocean.”

The press release, functioning as a sort of eulogy from the WHOI, stated, “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.”

It also dived down to the deepest known undersea vents along the Mid-Caymen Rise in a mission sponsored by NASA. Information the Nereus collected about extremophiles living by the vents was intended to aid in the search for extraterrestrial life. It's a cliché these days to say that we know as much about the surface of Mars as we do about the hadal zones of the world's oceans, but Nereus was a probe built to close that gap.

Jonathan Copley, a senior lecturer in marine ecology at University of Southampton, put up a nice piece on the multitude of robotic explorers that have been lost to the ocean. It's sort of a glimpse of a future world of robotic coworkers—or alternatively it may be just a glimpse into a present world where researchers rely on a really nice equipment to do things they've never been able to do before:

The loss of a remotely operated vehicle (ROV) or autonomous underwater vehicle (AUV) is utterly crushing for those aboard a research expedition and their colleagues ashore. But whenever we send something into the ocean depths, there is never an absolute guarantee that it will come back. There is always a risk involved, although we minimise risk through preparation and manage it in our expedition plans.

The only way to avoid risk completely is not to go at all; some risk will always be there, and that means that sometimes the dice will not roll in our favour.

It's quite possible Nereus rolled the old “16,000 pound per square inch” snake eyes and imploded. In a way, the danger of the kind of pressure that can crush a robotic sub really underscores why it's a good thing we have remotely operated and autonomous submarines in the first place.

"We are grateful to our partners for helping build such a breakthrough technological innovation in deep-ocean exploration and to the many engineers, technicians, and scientists at WHOI and around the world who helped realize our vision of a full-ocean-depth research vehicle," said WHOI President and Director Susan Avery. "Nereus may be gone, but the discoveries it enabled and the things it helped us learn will be an indelible part of its legacy."