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 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.
"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.
"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."
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.
