In 2021, the Hayabusa2 space mission successfully delivered a morsel of the asteroid 162173 Ryugu to Earth — five grams of the oldest, most pristine matter left over from the solar system’s formation 4.5 billion years ago. Last spring, scientists revealed that the chemical composition of the asteroid includes 10 amino acids, the building blocks of proteins. The discovery added to the evidence that the primordial soup from which life on Earth arose may have been seasoned with amino acids from pieces of asteroids.
But where did these amino acids come from? The amino acids flowing through our ecosystems are products of cellular metabolism, mostly in plants. What nonbiological mechanism could have put them in meteorites and asteroids?
Scientists have thought of several ways, and recent work by researchers in Japan points to a significant new one: a mechanism that uses gamma rays to forge amino acids. Their discovery makes it seem even more likely that meteorites could have contributed to the origin of life on Earth.
Despite their cachet as an essential part of life’s chemistry, amino acids are simple molecules that can be cooked up artlessly from carbon, oxygen and nitrogen compounds if there’s sufficient energy. Seventy years ago, famous experiments by Stanley Miller and Harold Urey proved that an electrical discharge in a gaseous mixture of methane, ammonia and hydrogen (which at the time was incorrectly thought to mimic Earth’s early atmosphere) was all it took to make a mixture of organic compounds that included amino acids. Later laboratory work suggested that amino acids could also potentially form in sediments near hydrothermal vents on the seafloor, and a discovery in 2018 confirmed that this does sometimes occur. [Continue reading…]