Dark Matter, AKA the Mystery of the Missing Mass, is the detective story of all detective stories. We think we know how the universe was created, and we have guesses about how old is might be...but we don't know what 90 percent of it is made of. In the 1930s, astronomer Fritz Zwicky determined the only way to explain the gravity you could see affecting stars and galaxies, was to conclude there must be far more mass out there than what is detected by our telescopes. Astronomers call this mass "Dark Matter" and have been searching for it ever since. Lately, that search has been heating up. Scientists have constructed maps of the universe showing where there are concentrations of dark matter.