Molecules of Life in Meteorites
Meteorites can carry amino acids, the building blocks of proteins—of life on Earth. What does the presence of these molecules in meteorites mean?
As early as the 1960s, researchers began to find amino acids in meteorites. But all amino acids are not created equal. Many kinds can be formed by the chemistry that happens naturally in space; only about two dozen are involved in life on Earth. And the amino acids involved in life have the special property of being “left-handed” as opposed to “right-handed.” So the question of which amino acids are found in meteorites—or comets or asteroids—is a crucial one.Intrigue started to build in the late 1990s, when researchers knew for sure that they had found more left-handed versions of important amino acids than right-handed versions in two meteorites. The same has since been found in more meteorites. And for some of them, researchers have made a link between the amounts of these amino acids and the amount of water present on the meteorite during its lifetime. “This gives us a hint that the creation of left-handed amino acids had something to do with alteration by water,” says Jason Dworkin, head of the astrochemistry lab at NASA’s Goddard Space Flight Center.
Since then, the findings have expanded beyond meteorites. In 2009, researchers identified the first amino acid in a sample from the comet Wild 2. Comets are of special interest because they may have delivered water some or all of the water to the ancient Earth. ”By looking at the ratios of different forms, or isotopes, of carbon, we could rule out the possibility that the amino acid was a contaminant from Earth,” says Jamie Elsila. “It’s a remnant that dates back to when the comet formed billions of years ago.”
Excerpt contributed by Liz Zubritsky, NASA