Researchers at the University of Colorado at Boulder have solved a major galactic mystery that may help astronomers in their quest to develop a detailed picture of the chemical evolution of the Milky Way galaxy. Speaking at the 204th meeting of the American Astronomical Society held May 30 - June 3 in Denver, the researchers reported that the abundance of deuterium, a heavy form of hydrogen, in the Milky Way galaxy today shows a consistent pattern that can be simply explained, lifting a veil of uncertainty that has long plagued astronomers.