Filmmaker and deep-ocean enthusiast James Cameron (Avatar, Titanic, The Abyss, etc.) recently became only the third human being to visit the deepest point on Earth’s surface: the Challenger Deep in the Marianas Trench. The first humans to visit the bottom of the ocean were Don Wash and Jacques Piccard, who made the journey in the submersible Trieste in 1960. Cameron invested a significant amount of his own money in the construction of the new HOV (human occupied vehicle) Deep Challenger.

I am not particularly interested in the whole debate over whether Cameron’s voyage to the depths is merely a “rich man’s junket”, because frankly…if I had that kind of money, I might consider a trip like that myself. (My tip jar is at the right of the screen, on the off chance you want to send me to the bottom of the ocean. Insert jokes about bringing me back.) Exploration and adventure have always been strong motivators in human history, and personally I would rather see people going on trips like this than, say, traveling to a new land for the purpose of plundering it and enslaving its population (another strong motivator in human history).

However, another side of Cameron’s adventure was highlighted in two articles, both excellent:

• In “James Cameron’s Deep Sea Challenge: a scientific milestone or rich guy’s junket?” , Al Dove and Craig McClain (in Deep Sea News) argue that human-based exploration is necessary. They laments the lack of investment in manned deep-sea vehicles. Until Deep Challenger, the only functional deep-sea HOV is Alvin, built 48 years ago. (Bonus: they use the term “hooptie”.) See also “10 Reasons We Should Explore the Deep” by the same authors.

• “I sing the praise of my robot underlings, the workhorses of deep sea exploration” by Southern Fried Scientist (which is a great pseudonym!) points out that many of the greatest discoveries in recent years—thermal vents, deep-ocean reefs, etc.—have been made via ROVs (remotely operated vehicles) which don’t carry humans, although operators do steer them (if not always in real time).

A strong argument in favor of HOVs is that humans can dynamically steer the mission, reacting to things that are unanticipated in real time. In addition, the romance factor is significant: the personal accounts of Cameron and other explorers are thrilling. However, building ROVs is a lot easier: you don’t need to put in oxygen tanks, make reinforced pressurized hulls to withstand the extremely high water pressure (as much as a thousand times the sea-level atmospheric pressure!), and the like. ROVs don’t get “the bends”, the release of gas as the body decompresses during ascent, and if they fail, nobody dies.

The obvious parallel for me, given my interests, is space exploration, and the arguments for human-based spaceflight sound remarkably similar. There are significant differences as well: going into low-Earth orbit is simpler in many ways than going to the depths of the ocean, since the difference in pressure is one atmosphere (as opposed to hundreds or thousands of atmospheres). However, even a long deep-sea jaunt is measurable in hours, not days or months—as trips to the Moon or Mars must be. Nevertheless, the arguments for sending humans into space sound the same as those for HOVs: the romance of exploration, which inspires us to think beyond the everyday, and the flexibility of reaction if something new comes up. No real-time communication with robotic probes can happen: it takes minutes or hours for signals to travel from distant planets back to Earth, which means ROV probes ideally should have some degree of autonomy. If something goes wrong (as with Spirit), it may not be possible to intervene.

At the same time, there are things only robots can do. No human-occupied spacecraft could stay in orbit around Saturn as long as Cassini has, or endured on the surface of Mars as long as Opportunity. Any spaceship with humans aboard would never chart a course into interstellar space like the Pioneer or Voyager probes (at least without solving the major problems that currently prevent interstellar spaceflight!). We don’t know enough about micrometeors and other hazards astronauts heading to Mars or beyond might face.

However, long-time readers of this blog also know that I’m not immune to the allure of space travel: I applied to be an astronaut, after all. (In case you’re wondering, I haven’t heard back yet, either way. No one-way trips to Pluto for me just yet.) As with deep-sea exploration, there seems to be room for both human-based and robotic space adventures. Romance isn’t strictly the province of placing humans in danger, and if you don’t believe me, tell me the image of Saturn on the right isn’t romantic. The essential thing is to continue to invest, to push boundaries, to keep the spirit of exploration alive—this can and should include robotic probes and deep-sea ROVs.

Finally, as a final illustration of the intertwined interests of marine scientists and space exploration, here’s an amazing animation from NASA’s Goddard Space Flight Center of Earth’s ocean currents: