It might be weird to think about molecules as expressing "handedness." After all, molecules don't have hands. But there is a class of organic molecules known as chiral molecules that can be thought of as being either left-handed or right-handed, similar to the way we favor one appendage over the other.
Basically, chiral molecules with different handedness will share the same chemical structure, but with different geometries. They're essentially arranged as mirrors of one another, in such a way that they're non-superposable. So it's impossible to flip one to make it match the other.
"When you shake somebody's hand, your right hand shakes another right hand, and it forms that nice, interlocking gesture; if you try to shake a left hand with your right hand it's a little awkward because the interaction is different," explained Brett McGuire, a researcher at the National Radio Astronomy Observatory in Virginia. "Chiral molecules work the same way."
These molecules aren't just peculiar for their geometric diversity, but they're actually essential to all life on Earth. Even stranger, most chiral molecules exist largely in a single formation on Earth, even though when you create them chemically from scratch, both varieties will form. So for some bizarre reason, life on Earth seems to have a preference for left-handed chiral molecules.
Scientists aren't entirely sure why this is so, but some important clues might lie in a recent discovery, which found that chiral molecules essential to life on our planet can also be found in deep space, in regions near the center of the Milky Way, reports Space.com.
"This [discovery] is going to provide us with a laboratory to try to test theories about the role that chiral molecules played in the origins of life here on Earth and how that chirality might play a role in the origins of life elsewhere in the galaxy," said McGuire, who also co-authored on the study.
The research pinpointed the presence of the chiral molecule propylene oxide within a distant star-forming cloud of gas called Sagittarius B2 using the National Science Foundation's Green Bank Telescope in West Virginia and the Parkes radio telescope in Australia. Though the measurements don't yet indicate whether these distant molecules are right- or left-handed, future studies should be able to make that discernment.
If they do turn out to be predominantly left-handed, it could help explain life's preference here on Earth. If even a slight preference is found for left-handedness in the depths of the galaxy, perhaps life on Earth just glommed on to this bias and ran with it.
"If we want to understand where and how this started... we have to look at the gas clouds where these molecules formed from," explained Brandon Carroll, another co-author of the study.
Such a galactic bias could be unique to our Milky Way, and it's possible that alien lifeforms throughout our galaxy could also share our Earthly preference for left-handed chiral molecules. It's interesting to think about — a sort of chemical brotherhood that might exist, unifying all neighboring life.