Robotic Mission Dives to Deepest Part of Ocean

By Rosanne Skirble Washington, D.C. 19 June 2009

Prior to the test run of a new robotic vehicle last month, underwater research vehicles operated no deeper than 6,000 meters. Nereus changed that.

The newly developed hybrid ROV Nereus is launched from the RV Kilo Moana during a test cruise in 2007 off Hawaii

The robotic craft, developed and operated by Woods Hole Oceanographic Institution, dove to 10,902 meters in the western Pacific, pushing the frontiers of exploration into unknown depths, says Andy Bowen, project manager for the Nereus Robot Development Program.

"Nereus is a tool which we hope the scientific community will use to make important discoveries about that final 4,000 meters of the ocean," he says.

Bowen says the hybrid design allows Nereus to be operated remotely while tethered to its mother ship or to run as a free-swimming craft controlled by onboard computers.

Nereus's specialized manipulator arm samples sediment from the deepest part of the world's ocean - the Mariana Trench

"It performs a series of routine surveys gathering routine information about the sea floor, using sensors such as sonar and digital photography to map out the area of interest in great detail."

Using these maps, scientists onboard the surface ship direct Nereus in its tethered mode through a fiber-optic cable. Bowen explains this lighter cable replaces the steel reinforced copper wire cables used by traditional robotic systems.

"We are able then to go in with a mechanical arm and high-quality cameras and actually interact directly with the sea floor under human control."

Because the 40-kilometer-long tether is so light - it weighs less than a kilogram and is nearly as thin as a human hair - it does not snap under its own weight and can withstand the crushing pressure of the deep ocean. The cable uncoils from both ends - a canister onboard the robot and one attached to the surface vessel.

WHOI biologist Tim Shank (at right) and Patty Fryer (left), a geologist with the University of Hawaii, examine the samples retrieved from the Mariana Trench

"And so as the vehicle goes about its business, it is essentially trailing a piece of glass fiber behind it, which allows us to range freely while remaining in contact with the surface ship. And that's really the big breakthrough with the Nereus system. At the end of the mission, we actually cut the fiber and then bring the end onboard the ship and dispose of it and recharge the batteries, and we're ready to go again."

Nereus weighs 3 tons and is just over 4 meters long and 2 meters wide. It is powered by 4,000 lithium batteries. The craft carries ballast weights in its descent to 11,000 meters, diving at 20 to 30 meters a minute for eight hours. The weights, Bowen says, are dropped on the sea floor.

"It really neither sinks or floats and using its propulsion system, which is a series of small propellers, we can actually drive the vehicle around near the sea floor much in the same way you might think of a helicopter. And that driving is done by a pilot 7 miles [11 kilometers] away on the surface vessel through a joystick."

The Challenger Deep in the Mariana Trench is located near the island of Guam in the west Pacific. It is the deepest abyss on Earth at 11,000 meters

Last month, Nereus dove nearly twice as deep as previous submersibles to reach Challenger Deep in the Mariana Trench, the deepest known place on earth. It's here near the Island of Guam in the Western Pacific that many of the world's volcanic eruptions and earthquakes occur. Andy Bowen says the mission's success paves the way for new scientific discoveries and ocean theories.

"Certainly, the role, for example, of the trench in the carbon cycle; how carbon is recycled within the [earth's] crust. Things such as earthquakes, various other chemical processes are an important part of coloring in a picture about the ocean that is critically important to our understanding of the global environment."

During its 10-hour dive to Challenger Deep, Nereus sent back high-quality video, gathered rocks and samples of deep ocean sediments and returned with microbes and small worms that live in extreme depths. But, Bowen says, Nereus has barely scratched the surface of the ocean floor, and he expects a research team to mount an expedition with Nereus within a year.