James Cameron recently touched down at Challenger Deep while Virgin empire chief Richard Branson and former Google CEO Eric Schmidt are funding other deep ocean submersibles. Last week, Amazon CEO Jeff Bezos announced that he would be dredging up Apollo 11’s engines from the deep Atlantic.

The first question I’ve got – one that seemed largely ignored as the news broke – is: Why? What is the value of recovering a twisted mass of unrecognizable metal? And where does this process stop; why not track down other used engines? Would jettisoned components of Sputnik’s, Yuri Gagarin’s, or Alan Shepard’s rockets be any of any less historical interest?

Bezos’ mission may be particularly quixotic, but it highlights a growing trend. So what is it about the deep sea that is so alluring to today’s billionaires?