Tim Macdonald is used to enormous pressure. Much of his training has been specifically about dealing with it. That’s because the Australian engineer and submarine pilot is vitally involved in researching the least understood parts of our world, which is to say those in the hadal zone.

Named after Hades, Greek god of the underworld, these are the dark, cold, mysterious areas of the ocean below 6000 metres. Last year, Macdonald and Kiwi Rob McCallum joined submarining’s most exclusive club when they took the $US30 million ($42.7 million) vessel Limiting Factor down 10,925 metres to Challenger Deep, the lowest part of the Mariana Trench.