Life tends to be left-handed. Certain molecules have mirror-image versions of themselves that act differently, just as a left hand canāt fit in a right glove. This chemical property, known as chirality, is found within all organic life, and sticking with one handedness is thought to offer an evolutionary advantage. But its origins remain a mystery.
Now a team led by of the National Radio Astronomy Observatory in Virginia and Brandon Carroll at the California Institute of Technology have detected the first chiral molecule in interstellar space. They spotted propylene oxide within an enormous star-forming cloud of gas and dust only 390 light-years away.
That result alone excites , a geochemist at the University of Virginia who has worked extensively on chiral molecules found within meteorites.
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āWe must have chirality for life,ā says Macko. Although propylene oxide isnāt itself necessary for life, āif you can have chiral molecules of this nature, that means that thereās probably molecules that we associate with life too,ā he says.
One handedness
But McGuire and Carroll are excited not just because the result could help scientists understand where life can arise, but it could also tell them about how it happened. āThe really cool thing is that lifeĀ ā for reasons we donāt understandĀ ā selected one chirality for some of its molecules over another,ā says McGuire.
Amino acids, for example, are always left-handed, whereas the sugars that make up DNA are always right-handed. The team donāt yet know which handedness, if any, dominates for the interstellar propylene oxide, but further observations could shed light on why nature chooses one handedness over the other.
Carroll suspects that nature first produced an equal number of right- and left-handed molecules. Both are easily synthesised in the lab. Then some process, perhaps incoming star light, preferentially destroyed one handedness, leaving only the other to form life.
āWe just donāt know what process is doing this,ā says Carroll. āIt could be completely random. Or it could be that theyāre all the same.ā But by observing how these molecules naturally form deep within clouds of interstellar gas, researchers might soon have their answer.
Journal reference: Science, DOI:
