The launch of preparatory drilling for methane hydrate off Aichi Prefecture last month drew public attention amid hopes it will become an alternative to nuclear power at a time when Japan's self-sufficiency rate in energy is a meager 4 percent.

While the potential of methane hydrate is still unclear, the government aims to establish technical bases for commercial use in fiscal 2018. Here are some basic questions and answers about methane hydrate and Japan's efforts to develop it as an energy source.

What is methane hydrate?