NASA Scientists Want to Solve a Mystery: Why Did Life "Turn Left?"
Arthur T Knackerbracket has processed the following story:
[...] For Danny Glavin, a senior sample scientist, he wanted to solve a relentless mystery in his life's work: Why are all known living things only based on the left-handed forms of amino acids, the molecules that build proteins?
His moment arrived nearly a decade later. Glavin and a team of researchers probed the grit from Bennu, a carbon-rich asteroid made of loosely bound boulders, but what they found threw them a curveball. Rather than supporting one of the leading hypotheses - that the early solar system favored the left-handed variety and brought those ingredients to primitive Earth - it showed no favoritism at all.
[...] Many amino acids, whether they're used in biology or not, come in two mirror-image forms. Each molecule has a central carbon atom with other atom groups attached, oriented in one direction or the reverse. This property, called chirality, is like a left and right hand: They're similar, but if you stacked them, the thumbs would be hitchhiking opposite ways.
In Earth life, the amino acids are always "left-handed," and sugars, which partly make up the backbone of DNA, are always right-handed, giving the double helix its signature twist to the right. The homogeneity found among both is especially confounding to scientists because the left and right-handed versions of all these molecules are equally available in nonliving chemical mixes.
Practically speaking, if all biological molecules took the reverse form, that might work just fine. So if life could have taken the other path, why didn't it? Is uniform "handedness" a secret ingredient in the recipe for life, and more specifically, did it have to turn left? Did the bias toward left-handed amino acids begin in the cosmos, or did it happen later on this planet?
"A fundamental question for all of us is whether life had to be the way it is," said Iris Chen, professor of chemical and biomolecular engineering at UCLA, who wasn't involved in the asteroid study. "Is the universe predisposed to our kind of life, or is our biology the result of accidents and chance?"
Scientists knew early on they would use the material collected by NASA's $800 million OSIRIS-Rex mission, short for Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer, to analyze the "handedness" of individual amino acids. Bennu's mineral fragments could be older than the 4.6 billion-year-old solar system. These grains of stardust could have come from dying stars or supernovas that eventually led to the creation of the sun and planets.
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