Unmanned sub touches deepest part of world's ocean Explores Mariana Trench, more than 10 kilometres below surface of Pacific Ocean
Nereus was tested in the waters off the dock of the Woods Hole Oceanographic Institution in Massachusetts in April before being sent to the spot known as Challenger Deep in the Pacific's Mariana Trench. At 11,000 metres below sea level, more than 1,600 metres deeper than Mount Everest is high, Challenger Deep is arguably one of the most remote locations on Earth. (Tom Kleindinst/Woods Hole Oceanographic Institution) Nereus was tested in the waters off the dock of the Woods Hole Oceanographic Institution in Massachusetts in April before being sent to the spot known as Challenger Deep in the Pacific's Mariana Trench. At 11,000 metres below sea level, more than 1,600 metres deeper than Mount Everest is high, Challenger Deep is arguably one of the most remote locations on Earth. (Tom Kleindinst/Woods Hole Oceanographic Institution)
An unmanned robotic vehicle has successfully touched the deepest known part of the ocean floor, U.S. researchers revealed on Wednesday.
On May 31, the Nereus was launched off the research vessel Kilo Moana in the western Pacific Ocean, between Papua New Guinea and Japan.
The unmanned aquatic vessel descended 10,902 metres into a part of the Mariana Trench known as Challenger Deep. It is the first vessel to explore the remote area in more than a decade.
"It's the deepest known part of the ocean," said Andy Bowen, project manager of the Woods Hole Oceanographic Institution, which led the dive. "The trench is virtually unexplored, and I am absolutely certain Nereus will enable new discoveries."
With a budget of $8 million US, the Nereus dive was the first voyage into the trench since a Japanese-built robot named Kaiko attempted a voyage in 1998. That robot disappeared when the cable connecting it snapped on a dive during a typhoon in 2003.
Measuring a little more than four metres in length, Nereus was able to take pictures and video of the ocean floor and bring back samples of sea life, including shrimp and a sea cucumber.
"The samples collected by the vehicle include sediment from the subducting and overriding tectonic plates that meet at the trench," said Patty Fryer, a geologist with the University of Hawaii.
Water pressure in the trench is more than 1,000 times what it is on land at sea level. The nearly 11,000 metres that Nereus was able to dive is approximately the same as the cruising altitude of a commercial airliner and roughly two kilometres more than the summit of the tallest point on earth, Mount Everest.
Researchers are excited about the potential to investigate such extreme conditions.
"The ocean's deepest regions [were] previously inaccessible" said Julie Morris, the ocean sciences division director of the U.S. National Science Foundation. "We're very pleased with the success of these sea trials."
Connecting tether was the width of a human hair
Nereus was able to succeed where other devices had failed because of a unique new design, researchers say. The unmanned vehicle is remotely operated by pilots aboard a surface ship via a lightweight, micro-thin, fibre optic tether. But Nereus can also be turned into a free-swimming, autonomous vehicle even at great depths.
Conventional diving systems use steel-reinforced cables to maintain control of the probe, but such systems would snap under their own weight in the pressure conditions of the Mariana Trench. The tether the Nereus used during its 10-hour stint on the ocean floor used a combination of fibre optic cables and plastic sheath and was roughly the same diameter as a human hair.
Testing will continue over the next few days, and the team will return to port on June 5.
A Woods Hole Oceanographic Institution (WHOI) remotely operated vehicle touched down 10,902 meters (35,767 feet) in the Mariana Trench near the island of Guam.
Mariana Trench 

On Sunday, May 31, Nereus dove into the Pacific Ocean and began its descent into Challenger Deep the deepest area of the Mariana Trench.

"It's the deepest known part of the ocean. The trench is virtually unexplored, and I am absolutely certain Nereus will enable new discoveries," said Andy Bowen, project manager of WHOI, "Reaching such extreme depths is the pinnacle of technical challenges. The team is pleased that Nereus has been successful in reaching the very bottom of the ocean to return imagery and samples from such a hostile world. With a robot like Nereus we can now explore anywhere in the ocean. The trenches are virtually unexplored, and Nereus will enable new discoveries there. Nereus marks the start of a new era in ocean exploration."

However, this is not the first time that a mission was sent into the trench. In 1998, the Japanese robot Kaiko was launched. In 1960 a two man bathyscaphe vehicle, the Trieste descended 10,916 meters (35,813 feet) to the ocean floor.

Nereus can be operated remotely or it can run as an autonomous underwater vehicle AUV. It is currently attached to the mother ship via an optic tether the diameter of a human hair.

"Much of the ocean's depths remain unexplored. Ocean scientists now have a unique tool to gather images, data and samples from everywhere in the oceans, rather than those parts shallower than 6,500 meters (4 miles). With its innovative technology, Nereus allows us to study and understand previously inaccessible ocean regions," said Julie Morris, director of the National Science Foundation (NSF)'s Division of Ocean Sciences.  NSF assisted with the US$8 million project funding.

Nereus will send videos and collect samples on the ocean floor at the trench's subduction zone and area during its mission.

"The samples collected by the vehicle include sediment from the tectonic plates that meet at the trench and, for the first time, rocks from deep exposures of the Earth's crust close to mantle depths south of the Challenger Deep. We will know the full story once shore-based analyses are completed back in the laboratory this summer. We can integrate them with the new mapping data to tell a story of plate collision in greater detail than ever before accomplished in the world's oceans," said geologist Patty Fryer of the University of Hawaii.