Panspermia is the idea that life, or material essential to life’s development, somehow reached Earth from outer space. Whether our planet was dusted by a passing comet or pockmarked by angry little asteroids, the theory holds that the molecules needed to create the most basic living things (“replicators”) could not have occurred in an early Earth environment. They must have been deposited from elsewhere in the universe. This week, researchers announced that they used a powerful telescope called the Green Bank Telescope to identify two of the most sought-after life-forming molecules — and they’ve found them floating on ice grains near the center of the galaxy.
The data, much of which was collected by undergraduates participating in a summer program at the telescope, come from a gigantic gas cloud some 25,000 light years away, and thanks to a new spectroscopic method of identifying molecules in gasses. Called rotational spectroscopy, the technique works by recording the distinctive ‘fingerprint’ of microwave radiation given off by molecules in a gas. Such free-floating units can switch freely between a set of discreet rotational states, and as they do they emit or absorb radio waves with a very specific level of energy.
By comparing this interstellar fingerprint to those from known (or desired) molecules, astronomers can identify the gas even when, as in this case, those molecules are nearer to the galactic core than to Earth itself. This technique only works for gases, unfortunately, but that makes it a perfect method for peering into outer space — or into the atmospheres of distant worlds.
The two molecules in question are cyanomethanimine, a precursor to the DNAbase adenine, and ethanamine, precursor to the amino acid alanine. Both adenine and alanine are widely referred to as necessary for the formation of life, though in reality only something chemically quite like these molecules might be needed.
Even on Earth, life has evolved a substitution for one letter of the genetic code — switching Thymine’s “T” in DNA for Uracil’s “U” in RNA — and this split occurred so long ago biologists have yet to pinpoint its precise date of emergence. There’s no reason to believe that some hypothetical alien life form might need adenine or alanine, specifically. It would be more accurate to say that life requires molecules with some or all of the useful properties of these molecules, and that the forms found in life on Earth might simply be the ones most likely to form spontaneously.
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