Woods Hole Oceanographic Institute (WHOI) says its deep sea unmanned submersible 'Nereus' has gone missing 10km down while exploring one of the world's deepest spots – the  Kermadec Trench, located north east of New Zealand. Surface debris was found, suggesting the vessel suffered a catastrophic implosion as a result of the immense pressures where it was operating.

The WHOI apprises that everything was going fine, then the camera feeds abruptly went dark, and the researchers lost communication with the vehicle.

Apparently they were not particularly worried: it had happened before and the vehicle designers had planned for something like this. Whenever Nereus lost contact with the surface, it was programmed to wait 30 minutes so that the ship could be moved a safe distance away before the sub dropped its ascent weights.

Eventually, one of the ship’s crew spotted some white objects in the water. Then more. The rescue boat went in and three crew members began scouring the surface with nets as more and more white dots appeared. By then it became clear that Nereus was gone.

The US$8-million robot was built in 2008 and could operate in an autonomous mode or remotely controlled via a tether to a support ship to explore the Earth's deepest oceanic trenches, and was a flagship ocean explorer for US oceanographers.
 
Source: WHOI