Finding Chirality

The Sagittarius B2 North molecular cloud, seen rising over Lake Waiau on the summit of Mauna Kea, contains a chiral molecule. 

BRETT A. MCGUIRE

Many molecules on Earth that are otherwise identical come in two mirror image forms—like right and left hands. This property is known as chirality. For some molecules, singular handedness—known as homochirality—has been prevalent. The origin and the evolutionary advantage of molecules all conforming to the same orientation have been a mystery. For the first time, researchers have found evidence of a chiral molecule in space, indicating that chirality is not unique to Earth and hinting at its source in interstellar matter. 

A team from the National Radio Astronomy Observatory, the California Institute of Technology, and Harvard, led by astrochemists Brett McGuire and Brandon Carroll, looked for radio wave signatures of the chiral molecule propylene oxide in the frequently-studied Sagittarius B2 North molecular cloud, some 28,000 light years from Earth. They chose to search for propylene oxide because it is one of the simplest and lightest chiral molecules, making it easier to detect using radio astronomy. 

The molecular structure of propylene oxide causes a unique wavelength reading across three different radio frequencies. The Green Bank Telescope in West Virginia was able to measure two of the key frequencies, while the Parkes Radio Telescope in Australia contributed the third. In all three frequencies, researchers found wavelengths consistent with the presence of propylene oxide. Since the odds of three separate wavelengths showing signatures of the molecule in its absence are roughly one in seventeen million, the study’s authors concluded that propylene oxide is present in space. 

The next step will be to determine if propylene oxide’s left– or right-handed version is more prominent. Many chiral molecules involved in biological processes occur in only one form. For example, amino acids, which make up proteins, are nearly all left-handed, while right-handed amino acids are rare and found only in bacteria. According to McGuire and Carroll, an excess of one chiral form in space could “be the push that decided what handedness life on Earth uses, and what life in other parts of the universe may use.” (Science

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