Space.com (August 16, 2010)
"A mysterious bias in the way the building blocks of proteins twist could be due to supernovas, researchers now suggest.
"If correct, this could be evidence that the molecules of life weren't created on Earth, but came from elsewhere in the cosmos.
"Organic molecules are often chiral, meaning they come in two versions that are mirror images of each other, much as right and left hands appear identical but possess reversed features.
"Curiously, on Earth, the amino acids that form the proteins for life are virtually all 'left-handed,' even though it should be as easy to make one version as the other. Even more strangely, samples of certain amino acids obtained from the Murchison meteorite were mostly left-handed also, suggesting there could be a bias for left-handed amino acids throughout the rest of the cosmos...."
Or, not so strangely. The Murchison meteorite, and Earth, have been spending a whole lot of time in the Milky Way galaxy. Which is a place where supernovas go off on a fairly regular basis.
That's where this latest big of informed speculation gets started:
"...As stars collapse right before they become supernovas, they generate an intense burst of electron antineutrinos that the researchers suggest would preferentially interact with nitrogen atoms in right-handed amino acids. All atoms possess 'spin,' and the handedness of an amino acid can influence how the spin of the nitrogen atoms within them align.
"The antineutrinos, possessing a spin of their own, would prefer to interact with the way nitrogen atoms spin in right-handed amino acids rather than left-handed ones, since the spins of the antineutrinos and nitrogen atoms would align.
"As a result, the antineutrinos would preferentially convert the nitrogen atoms in right-handed amino acids into carbon atoms. Boyd and his colleagues suggest this would result in the destruction of right-handed amino acids, leaving only the left-handed versions behind...."
There's a paragraph about the effect on neutron stars' magnetic fields on the (extremely thin) clouds of gas around them, too.
The bottom line seems to be that, given time, a mix of amino acids in one of those clouds of molecules may be 'filtered' by antineutrinos and maybe magnetic fields, until what's left are the left-handed set we use.
Which means that if there's life elsewhere, it may not be all that different from us - at least on the molecular level.
- "Life's Sinister Origins: Comets?"
(September 29, 2009)
- "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence"
(May 29, 2009)
- "DNA - A Universal Pattern? Could Be"
(April 8, 2009)