Proteins made from amino acids drive the chemical gears of life. Scientists are eager to understand the origin of amino acids because of their connection to living things. After all, amino acids may have helped give rise to life on Earth after being transported here by asteroid or comet fragments some 4 billion years ago.
If so, were comets or asteroids responsible for amino acid production? Or did the building blocks of life originate from the icy, gaseous and dusty interstellar molecular cloud that gave rise to our solar system and countless others?
In a new study, scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, sought to investigate how amino acids and amines — their chemical cousins – may have been formed. They approached this by simulating the aqueous change of the parent body of meteorite from interstellar residue analogues.
To simulate the conditions they would have encountered in asteroids, the scientists created ice similar to that found in interstellar clouds, irradiated them with radiation, and then exposed the remaining material, including amines and amino acids, to water and heat.
The ice was made using molecules that telescopes have commonly detected in interstellar clouds, such as water, methanol, carbon dioxide and ammonia. Later, scientists used a Van de Graaff particle accelerator at Goddard to zap the ice with high-energy protons to mimic the cosmic rays the ice would have experienced in a molecular cloud.
Simple molecules were split apart by the radiation process. These molecules reassembled to form more complicated amines and amino acids, such as glycine and ethylamine. There were sticky residues of the amino acids.
Danna Qasim, who worked on this experiment when she was a postdoctoral fellow at NASA Goddard from 2020 to 2022, said: “We expect these interstellar cloud remnants to be transferred to the protoplanetary disk creating a solar system, including asteroids.”
Next come asteroid simulations.
Scientists were able to reproduce the “aqueous modification” conditions in some asteroids billions of years ago by immersing the residues in water tubes and heating them to different temperatures and for different periods of time. They then examined how the molecules responded to these warm, wet conditions.
They found that regardless of asteroid conditions, the types of amines and amino acids produced in interstellar lab ice and their amounts remained constant. This suggests that amines and amino acids can travel intact from the interstellar cloud to an asteroid.
However, each molecule responded to asteroid-like conditions depending on how much heat was provided and for how long by the scientists. For example, after simulating an asteroid for seven days, glycine levels increased, while ethylamine levels barely changed.
Numerous other scientists have created interstellar ice, exposing them to radiation. They’ve found that this mechanism produces amines and amino acids, just as the Goddard team did. However, the molecules made in laboratories differ from those in meteorites.
Materese said, “Laboratory experiments that focused solely on ice irradiation don’t fully reflect the reality of the chemistry these compounds experience. So part of the goal of this work was to see if we can close that gap.
The research team has not yet closed the gap. They found that even after simulating asteroid conditions, the amines and amino acids they produced still didn’t match those found in meteorites.
- Danna Qasim*, Hannah L. McLain et al. Meteorite Parent Body Aqueous Alteration Simulations of Interstellar Residue Analogues. American Chemical Association. DOI: 10.1021/acsearthspacechem.2c00274