Nereus was a special type of robot submarine built by the Woods Hole Oceanographic Institution (WHOI). Designed for research, it could operate at depths of up to 11,000 meters (36,000 feet). Its purpose was to explore Challenger Deep, the deepest known point in the ocean. Nereus was named after a Greek sea god, chosen in a contest by high school and college students. It began its journey to Challenger Deep in May 2009 and reached the ocean floor on May 31, 2009.
During that dive, Nereus reached a depth of 35,768 feet (10,902 meters), making it the deepest-diving vehicle in use at that time. It was also the first vehicle since 1998 to explore the Mariana Trench, the deepest part of the ocean.
On May 10, 2014, Nereus was lost while exploring the Kermadec Trench at a depth of 9,900 meters (32,500 feet). Communication with the vehicle stopped around 2 p.m. local time. Later, debris found at the site showed that the vehicle was crushed by the extreme pressure at that depth.
Hybrid design
A hybrid ROV can operate either without being connected to a ship or with a thin optical fiber cable that links it to pilots on the ship. Using the cable allowed the vehicle to dive deeply while moving easily. The optical fiber cable is about as thick as a human hair and can support up to 4 kilograms (8.8 pounds). It is made of a thin plastic layer covering a glass fiber core. The vehicle carried about 40 kilometers (25 miles) of cable stored in two small containers. This cable is smaller, lighter, and less expensive than other types of cable.
Nereus weighed about 3 tons and measured 4.25 meters (14 feet) long and 2.3 meters (8 feet) wide. It used around 2,000 lithium-ion batteries for power. Instead of the heavy syntactic foam commonly used in submersible vehicles, Nereus used carefully designed ceramic spheres. Each part of the vehicle’s body contained between 700 and 800 hollow spheres, each 9 centimeters (3.5 inches) in size, to handle extreme pressure. The vehicle had a lightweight robotic arm that used hydraulic systems to collect samples, even under intense pressure.
As an alternative to using the cable, Nereus could operate independently as an autonomous vehicle to explore the ocean floor.
When designing Nereus, the team led by Andy Bowen at the Woods Hole Oceanographic Institution used experience from creating autonomous underwater vehicles and tethered robots. They built a hybrid ROV that could move quickly over large areas of the ocean floor like an aircraft and then switch to hovering over smaller areas to conduct experiments or collect rock and sea life samples.
Deepest dive
The Challenger Deep is located in the Western Pacific Ocean near the island of Guam in the Mariana Trench, which is the deepest known part of Earth's oceans and the deepest place on Earth. In May 2009, the vehicle Nereus reached a depth of 10,902 meters (35,768 feet), making it the deepest-diving vehicle in operation at that time. It was the first vehicle since 1998 to explore the Mariana Trench. To complete this dive, the vehicle had to handle pressures more than 1,000 times greater than the atmospheric pressure at Earth's surface. It remained above the trench for over 10 hours and sent live video to the mother ship.
Nereus is the third vehicle in the world to reach the bottom of the Pacific Ocean's Challenger Deep. The first was the crewed Bathyscaphe Trieste, which carried U.S. Navy Lieutenant Don Walsh and Swiss engineer Jacques Piccard. It reached the Challenger Deep on January 23, 1960. The Nereus dive aimed to reach the same location. On March 24, 1995, a Japanese robotic probe called Kaikō made the first uncrewed trip to the Challenger Deep.
Once at the bottom, Nereus collected liquid and rock samples. Patricia Fryer, co-chief scientist of the expedition, provided comments about the samples.
Loss
On May 10, 2014, at about 2 p.m. local time, the submersible Nereus was lost during a dive to a depth of 9,900 meters (32,500 feet) in the Kermadec Trench. Scientists believe this happened because of the extreme pressure at that depth, which reached up to 110 megapascals (16,000 psi).
Nereus was part of the NSF-sponsored Hadal Ecosystems Study (HADES) project, led by Timothy Shank, a biologist from the Woods Hole Oceanographic Institution (WHOI). The submersible was controlled from the Research Vessel Thomas G. Thompson. Thirty days into a 40-day mission, about seven hours into a nine-hour dive, contact with Nereus was lost. After standard emergency recovery steps failed, the team searched the area near the dive site. They later found debris on the surface, which was confirmed to be parts of Nereus. This suggested a sudden and severe failure. The ship’s crew collected the debris to learn more about the cause of the failure. Despite this loss, Larry Madin, WHOI’s Director of Research, stated that WHOI will continue to design, build, and operate underwater vehicles for ocean exploration.