Scientists have discovered amino acids, the building blocks of life, in a meteorite where none were expected.
The finding adds evidence to the idea that some of life’s key ingredients could have formed in space, and then been delivered to Earth long ago by meteorite impacts.
“This meteorite formed when two asteroids collided,” said Daniel Glavin of NASA’s Goddard Space Flight Center in Maryland. “The shock of the collision heated it to more than 2,000 degrees Fahrenheit, hot enough that all complex organic molecules like amino acids should have been destroyed, but we found them anyway.”
Amino acids are the molecules used to build the proteins that are essential to life.
The proteins created from amino acids are used in everything from structures like hair to enzymes, the catalysts that speed up or regulate chemical reactions. Just as the 26 letters of the alphabet are arranged in limitless combinations to make words, life uses 20 different amino acids in a huge variety of arrangements to build millions of different proteins.
In previous missions, scientists found amino acids in samples of Comet Wild 2, and in various carbon-rich meteorites. Finding amino acids in these objects supports the theory that the origin of life got a boost from space.
The meteorite sample was divided between the Goddard lab and a lab at the Scripps Institute of Oceanography at the University of California, San Diego. “Our analyses confirm those obtained at Goddard,” said Jeffrey Bada of Scripps, who led the study there. The extremely sensitive equipment in both labs detected small amounts of 19 different amino acids in the sample, ranging from 0.5 to 149 parts per billion.
The team had to be sure that the acids in the meteorite didn’t come from contamination on Earth, and they were able to do so because of the way amino acids are made. Amino acid molecules can be built in two ways that are mirror images of each other, like your hands. Life on Earth uses left-handed amino acids, and they are never mixed with right-handed ones. The amino acids found in the meteorite had equal amounts of the left and right-handed versions.
The sample had various minerals that only form under high temperatures, indicating it was forged in a violent collision. It’s possible that the amino acids are leftovers from one of the original asteroids in the collision.
However, the team thinks it’s unlikely amino acids could have survived the conditions that created the meteorite, which endured higher temperatures over a much longer period.
“It would be hard to transfer amino acids from an impactor to another body simply because of the high-energy conditions associated with the impact,” Bada said.
Instead, the team believes there’s an alternate method of creating amino acids in space. “Previously we thought the simplest way to make amino acids in an asteroid was at cooler temperatures in the presence of liquid water. This meteorite suggests there’s another way involving reactions in gases as a very hot asteroid cools down,” Glavin said.
Fragments of 2008 TC3 are collectively called “Almahata Sitta” or “Station Six” after the train stop in northern Sudan near the location where pieces were recovered. They are prized because they are Urellites, a rare type of meteorite.
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