Granted, it might not seem like such a big deal when astronomers find some of the missing mass in the universe, since there's very little that isn't missing. Roughly 95 percent of the cosmos is either dark matter or dark energy. About five percent of the universe is made up of the normal mass we're familiar with—baryonic matter. Yet by adding up the known stars and galaxies and gas, astronomers have only accounted for about half of that five percent.