A robotic submarine named Nereus has become the third craft in history to reach the deepest part of the world's oceans, at the bottom of the Mariana Trench in the western Pacific Ocean.

The dive to Challenger Deep, an abyss within the Mariana Trench that reaches 11,000 metres beneath the waves, was completed on 31 May by a team from the Woods Hole Oceanographic Institution (WHOI), Massachussetts, US.

For the expedition, the team had to build a new breed of remotely-operated submarine, called Nereus, which is capable of going deeper than any other while still filming and collecting samples. Sunday's dive makes it the world's deepest-diving vehicle, and the first vehicle to explore the Mariana Trench since 1998.

So far only a single picture taken by Nereus at the bottom of the trench has been released,

Vast explorations

"Nereus is like no other deep submergence vehicle," says oceanographer Tim Shank of WHOI.

"It allows vast areas to be explored with great effectiveness. Our true achievement is not just getting to the deepest point in our ocean, but unleashing a capability that enables deep exploration, unencumbered by a heavy tether and surface ship, to investigate some of the richest systems on Earth."

"With a robot like Nereus, we can now explore virtually anywhere in the ocean," adds project manager Andy Bowen.

Third in line

Only two other vehicles have ever reached the bottom of Challenger Deep: US bathyscaphe Trieste, which carried Jacques Piccard and Don Walsh in 1960, and the Japanese robot Kaiko, which made three unmanned expeditions to the trench between 1995 and 1998. Trieste was retired in 1966, and Kaiko was lost at sea in 2003.