A robotic sub called Nereus has reached the deepest-known part of the ocean. The dive to 10,902m (6.8 miles) took place on 31 May, at the Challenger Deep in the Marianas Trench, located in the western Pacific Ocean. This makes Nereus the deepest-diving vehicle currently in service and the first vehicle to explore the Marianas Trench since 1998. The unmanned vehicle is remotely operated by pilots aboard a surface ship via a lightweight tether. Its thin, fibre-optic tether to the research vessel Kilo Moana allows the submersible to make deep dives and be highly manoeuvrable. THE NEREUS SUBMERSIBLE Weight on...