Researchers say they’ve found the first evidence of mirror-image molecules in interstellar space – a discovery that relates to the chemistry that gave rise to life here on Earth.
The molecules of propylene oxide were detected in a huge cloud known as Sagittarius B2 North, about 28,000 light-years from Earth, during a scan that used the Green Bank Telescope in West Virginia.
Mirror-image molecules are notable because they come in left-handed or right-handed molecular orientations, like the molecules that serve as the building blocks for life on Earth. That “handedness” is known as chirality.
“This is the first molecule detected in interstellar space that has the property of chirality, making it a pioneering leap forward in our understanding of how prebiotic molecules are made in the universe and the effects they may have on the origins of life,” Brett McGuire, a chemist with the National Radio Astronomy Observatory, said in a news release.
McGuire is one of the authors of a paper on the discovery that was published by the journal Science and discussed today in San Diego at a meeting of the American Astronomical Society.
The orientation of chiral molecules plays a key role for life on Earth. For example, amino acids can theoretically take on a left-handed or a right-handed orientation, but all of the amino acids used by earthly life are of the left-handed variety. Sugars can also swing left or right, but living cells use only right-handed sugars. Left-handed sugars still taste sweet, but they pass through the body without being metabolized. (They’re also expensive to make, which explains why l-sucrose isn’t used as an artificial sweetener.)
Complex chiral molecules have been detected in meteorites as well as comets, but it’s not clear exactly how they formed. Scientists surmise that chiral molecules like propylene oxide may arise when particles collide with each other and chemically react within clouds of dust and gas like Sagittarius B2 North.
The presence of propylene oxide molecules was confirmed by analyzing spectral information gathered by the Green Bank Telescope as well as the Parkes Radio Telescope in Australia. The observations were conducted as part of a program known as the Prebiotic Interstellar Molecular Survey, or PRIMOS.
Although propylene oxide is a chiral chemical, it isn’t used by life as we know it. In fact, it’s considered a toxic gas with carcinogenic properties. Nevertheless, learning more about interstellar chirality could reveal why it is that life’s chemicals tend to stick with one hand or the other, a characteristic known as homochirality..
McGuire and his colleagues couldn’t get enough data to determine whether the molecules were left- or right-handed, but future analysis of the cloud’s effect on polarized light could tell the tale.
In addition to McGuire, the authors of “Discovery of the Interstellar Chiral Molecule Propylene Oxide (CH3CHCH2O)” include Brandon Carroll, Ryan Loomis, Ian Finneran, Philip Jewell, Anthony Remijan and Geoffrey Blake.
