Like an ice that burns, methane hydrate is cold, white and would light up like a gas stove if held to a flame. And so much of the frozen fuel naturally blankets the seabeds off Japan and elsewhere that scientists say it could power the world for centuries.
Yet, as soon as researchers plumb the depths and pull the potentially revolutionary energy source to the surface, the frosty crystalized methane starts to fizz and bubble into oblivion as it warms up, gasifies and then dissolves into the ocean.
Most nations don't even bother exploring offshore reserves for lack of harvesting technology. But in resource-poor Japan, plucking the deep-sea bounty off its shores is more than science fiction -- it is a national initiative that the government hopes becomes reality in 15 years.