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• Jon commented on 25 Jun 2010:

  Hi Adam – Daniel gave me a heads-up to comment on your question, even though I’m in another zone, because I work in the deep ocean.

  The comparison that’s often made is that “we know more about the surface of the Moon / Mars / Venus than we do about the ocean floor”.

  And that’s true, partly because of the budget reasons that Daniel mentions, and also because we can observe and map the surface of the Moon / Mars / Venus from spacecraft that we send to orbit them. In the case of Venus, there are dense clouds, but we can “see” through them with microwaves to map the surface below directly in great detail.

  But we can’t actually map the ocean floor directly from any satellites orbiting the Earth, because we can’t “see” through all the water (microwaves won’t go through it, unlike the clouds of Venus). Instead, we can “guess” at what the ocean floor looks like, by measuing variations in the Earth’s gravitational field (which is affected by variations in how far the rocks of the Earth’s crust are from the satellite).

  But the maps we get of the ocean floor from that technique are just estimates (they can be wrong, because you also get variations in gravitational field from differences in what the rocks are made of, as well as how far they are from your satellite). And the techniques can’t resolve any features smaller than a few miles across.

  So the only way to survey the ocean floor is to use sonar from ships – or even better, sonar from underwater vehicles that get even closer to the ocean floor. The closer you get to the target you are surveying, the better the resolution of the map you get.

  Here’s an example: last year my colleagues and I were exploring the ocean floor around Antarctica from our research ship. We found a crater, a couple of miles across and a mile deep, that wasn’t on any maps of the ocean floor produced by satellites. No-one knew it was there until we went there and turned on our sonars to survey the ocean floor beneath us. I find that amazing – there’s nowhere on land you could find a geographical feature that big that we didn’t know about before. But in the deep ocean, there are loads of them still waiting to be discovered…

  Even then, having a map doesn’t tell you what is actually down there, such as the species that live there. For that, you have to actually get there with cameras on an underwater vehicle. And then you only get to see a tiny part of the ocean floor at any one time, so it will take centuries for us to survey all of it.

  So it’s not that we don’t have the technology – it’s just that the unexplored area of the oceans is so vast that it will take us centuries to explore it, even working all the time with all the research ships we have. Sure, we could do it faster if we had more ships (but they cost $$$).

  But another way, that I’m very interested in (and going to a conference about next week) is getting small, cheap robots to do the initial survey work for us – and then tell us when they find something “interesting”, for us to then investigate with our ships and subs. But that means teaching robots how to recognise something “interesting” – and that’s the new challenge!

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  • Daniel commented on 25 Jun 2010:

    Thanks, Jon, for chiming in at this level of detail!

    I agree that the statement “we know more about the surface of the Moon / Mars / Venus than we do about the ocean floor” is probably true, though I still have difficulties quantifying either, and I tend to think that our knowledge of what is between the surface and the floor of the oceans may still outweigh what we know about space.

    there is more to what we know of the sea than the ocean floor, while what we know about

    I can imagine that there is more to the sea than the ocean floor that we know than there is to the surface of the Moon / Mars / Venus

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    • Daniel commented on 25 Jun 2010:

      The two dangling sentence fragments at the end of the comment above should not have remained there. Sorry.

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