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Top Comments: Amino Acids in Space: How Are They Made? [1]

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Date: 2023-01-08

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Proteins are crucial to life. They form tissues and enzymes that life processes depend on. Proteins consist of long chains of the 20 naturally occurring amino acids. The sequence of amino acids dictates the structure of the protein, and hence its job in keeping you alive. Plants need to make all of the amino acids they need, but most organisms make at least a few of them, while the rest are provided by diet. However, amino acids are found in space, in places where living things have never been. Indeed, in 2021, the Hayabusa2 space probe returned a 5 gram sample of matter from the asteroid 162173 Ryugu. This matter has been essentially untouched since the Solar System began forming 4.5 billion years ago, but analysis revealed the presence of 10 amino acids. How did they form?

Now there are many non-biological ways of synthesizing amino acids, including the famous Miller-Urey experiment; organic chemists are even more clever at devising efficient ways to put such molecules together. But how can such molecules arise naturally in the cold isolation of deep space? A new study from Japan suggests gamma radiation may have been a spur.

Amino acids have been found in meteorites called carbonaceous chondrites, and it has long been proposed that the first amino acids on Earth could have been delivered by the impact of such meteorites during Earth’s early history. Through spectroscopy, it is known that simple organic molecules, such as alcohols and aldehydes, as well as water and ammonia exist in space, as constituents of nebulas, comets, and asteroids. These molecules are the building blocks of amino acids, but the reaction for form amino acids requires an energy source. What the Japanese scientists showed that gamma rays produced by the decay radioactive isotopes likely to be present in carbonaceous chondrites are capable of converting those molecular building blocks into amino acids. Now, gamma rays are very high energy, and they can and do destroy amino acids, but the scientists showed that over time, under the conditions of the experiment, more amino acids were produced than destroyed. Further, gamma radiation is capable of deep penetration of matter in general, and organic matter in particular. This suggests gamma rays could produce amino acids near the center of a carbonaceous chondrite meteor. If this is true, it potentially solves another problem with the idea of delivery of amino acids to Earth by meteors: how do they survive the heat of atmospheric entry rather than burn to a crisp? If they’re deep inside the meteor, they will survive.

So another piece of the puzzle of where the stuff of life may have come from has been discovered, and it may have been gamma rays, which are better known to destroy life rather than produce it.

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