BBC: Japan says it has successfully extracted natural gas from frozen methane hydrate off its central coast, in a world first.
Methane hydrates, or clathrates, are a type of frozen "cage" of molecules of methane and water.
The gas field is about 50km away from Japan's main island, in the Nankai Trough.
Researchers say it could provide an alternative energy source for Japan which imports all its energy needs.
Other countries including Canada, the US and China have been looking into ways of...