Two new studies published in the past week lend more weight to the theory that life, or at least its constituent parts, came from outer space. One bolsters the theory that left-handedness prevails in the cosmos, and another explains how the building blocks of life became left-handed in the first place.
Many amino acids, sugars and other molecular building blocks of life are chiral, meaning they have left-handed and right-handed versions. Like your hands, these are mirror opposite pairs that cannot be superimposed on each other. There’s really no reason for one to prevail over the other, but this symmetry breaking happens anyway; life on Earth is largely left-handed (though a recent study suggests its lower forms can be ambidextrous). In 2009, NASA researchers studied meteorites and found that left-handedness also seems to prevail throughout the cosmos. Last week, they said this quality can be found in an even wider range of space rocks than they thought.
“This tells us our initial discovery wasn’t a fluke; that there really was something going on in the asteroids where these meteorites came from that favors the creation of left-handed amino acids,” said Daniel Glavin of NASA Goddard Space Flight Center.
So something is going on — but what? French scientists may have an answer, which has to do with polarized light. Light oscillates in a given direction, like up or down, left or right. Polarized sunglasses cut down on glare by filtering out horizontally polarized light. But in space, light from distant stars is circularly polarized when it passes through magnetized dust clouds, according to a study published this week in Astrophysical Journal Letters. This circular polarization results in a corkscrew pattern.
Shine those curly rays of light on some water, ammonia and methanol ice, and you’ll get amino acids. Uwe Meierhenrich and colleagues at the University of Nice Sophia Antipolis in France performed just such an experiment with UV light, and they produced a teeny bit more left-handed amino acids than right-handed ones, according to the BBC. This would explain why there are more left-handed amino acids on meteorites, and therefore why life on Earth is so biased to the left.
But the overarching question — why does nature like lefties? — is still up for debate. One study last fall suggested supernovae were the culprit, because they spew a bunch of right-handed electron antineutrinos when they blow up. Further research is still needed to test this theory.