Astronomers have discovered the first chiral molecule in interstellar space (Science 2016, DOI: 10.1126/science.aae0328). The discovery of propylene oxide in an interstellar cloud sets the stage for astronomers to explore chemical processes that led to the preference of one enantiomer over another in the formation of biomolecules on Earth.
All organisms on Earth build their proteins almost entirely from left-handed enantiomers of amino acids. Scientists have long searched for the reason why life picked left-handed chirality over right-handed.
The famous Murchison meteorite, which formed around the same time as our sun and landed in Australia in 1969, contains an abundance of amino acids, a slight excess of which are left-handed. This is significant because only a few percent excess of one enantiomer would be enough to push life in a direction of exclusive left or right handedness.
Scientists want to know how far back this chiral preference extends in the history of the galaxy.
A multi-institutional team led by Geoffrey A. Blake of Caltech announced the discovery of interstellar propylene oxide at a press conference at the American Astronomical Society meeting in San Diego on June 14.
The group detected the molecule in the interstellar cloud Sagittarius B2 North, in which scientists have found one-third of the 180 known interstellar molecules. They found three characteristic radio frequency absorbance lines that definitively identify propylene oxide.
However, these observations don’t distinguish between enantiomers. So, the team said, the next step will be more extensive observations that are sensitive to circularly polarized light because different enantiomers preferentially absorb left- or right-circularly polarized light.
“This is a very exciting discovery for astrobiology,” says Stefanie N. Milam, an astrochemist at the Goddard Space Flight Center. “The detection of complex organic molecules in the interstellar medium, comets, and meteorites gives us tremendous insight into the ubiquity of organic or prebiotic chemistry across the galaxy.”