DeFlip Side #171: Life’s First Handshake

DeFlip Side #171: Life’s First Handshake.mp3

Welcome everyone. I’m Christopher DeFilippis and this is DeFlip Side.

Earlier this week, scientists announced a discovery that may go a long way to helping us unlock the mystery of how life on Earth evolved the way it did.

At the Summer Meeting of the American Astronomical Society in San Diego on Tuesday, researchers Brandon Carroll from Caltech and Brett McGuire from the National Radio Astronomy Observatory in Virginia announced the discovery of propylene oxide in the Sagittarius B2 stellar cloud, located 28,000 light years away, towards the center of the Milky Way. That’s right. They discovered the first chiral molecule seen in interstellar space outside of our solar system.

And I bet you’d find that news a lot more exciting if you knew what chiral molecules were, and what in the heck they have to do with the rise of life on Earth. So let’s back up.


The easiest way to understand chiral molecules is to look at your hands. Your left hand and your right hand seem to be the same, but they’re actually imperfect mirror images of one another. Just like your hands, complex molecules often come in two slightly different mirror image forms. They’re the same atoms bonded together the same way, but sometimes they’re right handed, and sometimes they’re left handed. In fact, chiral is the Greek word for hand.

Now, the molecules that form the building blocks of life on earth are predominantly left handed in their chirality. But we haven’t figured out why.

And that’s partly why the discovery of an interstellar chiral molecule is such a big deal. It shows that the cosmos is capable of producing complex molecules that are essential to biology. As researcher Brett McGuire said during the announcement:

“This 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.”

Put in other terms, the discovery of chiral molecules in deep space lends credence to the theory that the origins of life here on Earth are extraterrestrial. And I don’t mean that in a crackpot ancient aliens way. Step with me now into the distant past.

Way back when, the newly-formed and slowly cooling earth was awash in a primordial soup that was seething with prebiotic molecules. At some point, a meteorite came hurling down from space, carrying amino acids made up of primarily left-handed chiral molecules. After the collision, a biochemical bonanza ensued. The left-handed amino acids were fruitful and multiplied, giving rise to more complex proteins that eventually became the building blocks of life on earth. And by that I mean you and me and your dog and iguanas and duck-billed platypuses and every other creature that ever lived on this planet.

The meteorite theory has been around for a long time, but it never answered the basic question: why have left-handed chiral molecules become dominant in Earth fauna? Was this meteorite an anomaly, or indicative of a bigger picture of life in the universe?

As researcher Brandon Carroll said at the conference:

“There’s an interesting link here because if, say, even a few percent excess in one amino acid was delivered to Earth… this could be the tipping point that pushed life in a singe direction, and that gave life the push it needed to, say, use only left-handed amino acids. And so we’re very interested in this. But if we want to understand where and how this started, we have to go back even further than the meteorites. We have to look at the gas clouds where these molecules formed from.”

So Carroll and McGuire set their sights on Sagittarius B2 North. This stellar gas cloud is near the center of the Milky Way, and it has been such a scientific goldmine for detecting new molecules in space that astronomers have been studying it for more than a decade. So Carroll and McGuire started combing through the data, looking for a signs of a chiral molecule.

And they eventually found one called propylene oxide. Propylene oxide is commonly used in making plastics. But this unassuming collection of atoms has given us the first definitive proof that the interstellar medium can actually make chiral molecules.

Carroll and McGuire still don’t know whether the propylene oxide is right or left handed. That’ll be the question they try to answer next. Brandon Carroll:

“And that’s what we’re really excited about, because that will let us start to test theories about processes that might actually have chiral preference in the interstellar medium. So that maybe something like certainly polarized light in space actually preferentially destroys one handedness of molecule over another, and that imprints a preference on all the material formed in that cloud, and that is transferred to meteorites and eventually planets, and that can have an influence on the handedness of life that we see in that system.”

And so from the tiniest atoms do the largest universal truths arise.

Carroll and McGuire called their presentation “Life’s First Handshake,” a tongue-in-cheek nod to the chiral mysteries they’re attempting to unravel. But whether our left-handedness turns out to be an earth-bound quirk or indicative of the fundamental nature of life everywhere, making such a discovery will be worth much more than a handshake.