Earth may have underground 'ocean' three times that on surface

Here's the discussion: https://news.ycombinator.com/item?id=7885641

Here are other submissions:

https://news.ycombinator.com/item?id=7887576

https://news.ycombinator.com/item?id=7888125

https://news.ycombinator.com/item?id=7888473

https://news.ycombinator.com/item?id=7891348