From Scientific American:
Although it is possible such an excess originated with meteors that brought mostly one type of molecule or another to Earth early in its history, another hypothesis suggests the origins of chirality are much older. As reported in Science, McGuire and his colleagues have discovered a chiral molecule in interstellar space. The compound, propylene oxide, exists in Sagittarius B2, a cloud of gas and dust near the center of the Milky Way.
The observation shows that chiral molecules were present “way before solar systems,” says P. Brandon Carroll of the California Institute of Technology and a co-author of the paper. If these types of molecules were mostly right-handed, they could have seeded the formation of other right-handed molecules, ultimately including DNA, long before our sun first shone. If so, that right-handed excess could have been baked into Earth’s chemistry as it was forming rather than being added by meteors after the fact.
NASA astrochemist Stefanie Milam says the implications are “huge” for astrobiology because they suggest that at least some of the complex chemistry associated with life is present elsewhere in the universe. Others are skeptical. Arizona State University biochemist Sandra Pizzarello, who has studied chiral molecules in meteorites, says connecting the observations to DNA chirality could be difficult. “We are still left wondering what happens” on the long path between molecular clouds and the origins of life, she says.
McGuire is now testing whether a majority of the propylene oxide molecules are right- or left-handed.