Titanic sub: What debris has been found and what does it mean?

The US Coast Guard has announced that a field of debris has been found on the seabed near the wreck of the Titanic.

A robotic diving vehicle found major fragments of the sub on the seafloor about 1,600ft (480m) from the Titanic shipwreck on Thursday.

According to dive expert David Mearns, the debris includes “a landing frame and a rear cover from the submersible”.

The BBC’s science correspondent, Jonathan Amos leads us through what these findings suggest.