In 1992, instruments aboard the Cosmic Background Explorer (COBE) satellite showed that 99.97 percent of the energy of the universe was released within the first year of its origin. This evidence seems to confirm(证实)the Big Bang theory, which holds that the universe originated from a single violent explosion (a big bang) of a very small amount of matter of extremely high density and temperature. Astronomers also theorize that 99% of the matter in the universe is invisible， or dark matter， composed of some kind of matter that they cannot yet detect.