Asteroid collision, NASA Hubble Space Telescope picture….credit: NASA, ESA, D. Jewitt
Finding amino acids, the building blocks of life, in meteorites is not new. Finding them in a meteorite that is a fragment of an asteroid collision, a piece formed at more than two thousand degrees Fahrenheit (1100 degrees Celsius) – now that makes astrobiologists ponder. There should be no amino acids in this meteorite. All organic material should have burned off. The meteorite in question is the highly unusual 2008 TC3. This was the first asteroid to be tracked in space before it impacted with Earth. The fragments of the tiny (3-5 meters) asteroid, found October 7, 2008 in northern Sudan and known as “Almahata Sitta” are of a rare type of meteorite, ureilite, with a relatively high carbon content (3%) for a ‘stony’ meteorite.
A sample of this meteorite was divided between the NASA Goddard lab (Greenbelt, Maryland) and the Scripps Institution of Oceanography lab (University of California, San Diego) and the results are coming in. As reported by the Goddard lab in the journal Meteoritics and Planetary Science [ Extraterrestrial amino acids in the Almahata Sitta meteorite] very sensitive instruments detected 19 different amino acids. The quantities were very small, 0.5 to 149 parts per billion, but according to the traditional notion of how amino acids are formed (or destroyed), there should have been close to 0.0 parts per billion. Somehow, even in the heat of the asteroid collision, amino acids were formed. As is so often the case in science, it is the anomalies that cause scientists to look for new ideas.
However, some typical questions needed to be answered:
Perhaps the meteorite samples were contaminated with amino acids from Earth? Chirality answered this question. Say what? Chirality is the technical term used for ‘handedness’ as in left or right handedness of two mirror images. In this case, amino acids can come in two forms with a carbon atom on the left or the right side of the molecule. On Earth all amino acids are left-handed. Right-handed amino acids have been found only in space. The Almahata Sitta samples have both left and right handed amino acids – they had to be formed in space.
Perhaps one of the asteroids in the collision had a more favorable composition to preserve amino acids? The researchers think this is unlikely because of the enduring high temperature caused by the impact and the unlikely distribution of materials following the collision.
So what accounts for the amino acids? The traditional notion for amino acid formation in asteroids was to mix the right organic chemicals (essentially carbon, hydrogen, and oxygen) in a watery solution. Not likely in this meteorite. The research team thinks it could be the result of chemical reactions in gases that occurred as the newly formed asteroid cooled. Now it’s back to the lab for a round of experiments to see if this new hypothesis can be demonstrated.
Whether this particular hypothesis can be proven or not, the door is open to looking for other ways of amino acid formation. That this is even possible has great significance. It means that amino acids, which become the billions of proteins that make life, can be formed in more ways than one, which implies that they are more commonplace than we thought. In turn, this implies that the chances for life elsewhere in the universe are greater.