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Astronomers Find 'Handed' Molecule in Space

Propylene oxide isn't flashy, but it may hold some deep answers about life on Earth.

by Michael Byrne
Jun 15 2016, 1:30pm

Image: B Saxton/NRAO/AUI/NSF

Astronomers from Caltech have for the first time identified a chiral molecule—organic molecules that have mirror-image versions of themselves—in interstellar space, a finding that may have implications for one of the nagging sub-mysteries of how the whole life-on-Earth thing worked out in the first place, and how it might work out on other planets.

The molecule in question, which was identified through an analysis of radio telescope data, is propylene oxide, which is commonly used here on Earth in making plastic and as a fumigant in almond processing. It can be found floating around in a large cloud of gas near the center of the Milky Way.

Propylene oxide isn't flashy, but the excitement is more about what it represents, which is this very special property called chirality. The chirality of molecules corresponds to "handedness"—that is, different versions of the same molecule can be oriented in different ways, in much the same way that you have a right and a left hand. You can't superimpose a right-handed chiral molecule on top of a left-handed chiral molecule, even though they are in fact the same molecule made from the same parts arranged in the same way, only flipped. As it turns out, right-handed and left-handed molecules don't always react with other molecules in the same way.

Pharmaceutical drugs often exhibit this phenomenon. Some molecular mirror-image twins do about the same thing, but a lot are entirely different beasts. Ketamine, for example, has a twin called esketamine that's about twice as strong. The left-handed version of methorphan is a powerful opioid painkiller while its right-handed twin is cough syrup; Aleve, aka naproxen, has an evil twin that causes liver poisoning and has no painkiller properties at all.

Anyhow, you get the idea. This difference winds up being pretty important for life on Earth. A property called homochirality, in which all of the molecules of some substance share the same chirality, is found all over biology. The amino acids found within biological life are all left-handed and we don't really know why. Their right-handed versions, which don't participate in biochemical reactions, are exceedingly rare on Earth.

I'll let the video finish explaining, but this is exciting stuff. Spotting chiral molecules in space may bring us closer to understanding how things wound up like this on Earth. We don't yet know what the chirality of the propylene oxide in question is, but future studies may be able to find out by looking at the polarization of light passing through its host gas clouds. This information should help scientists understand whether life started out with a left-right imbalance or if this is something that was selected for over time by the development of life.