At least one prebiotic molecule, an ingredient for building life, can form in the harsh environment of interstellar space, away from stars and planets, new research shows.
The amino acid glycine – the simplest amino acid without which life cannot exist – was thought to require star irradiation. New laboratory experiments show that it can be formed through what is known as “dark chemistry”, which is carried out without vigorous irradiation.
Glycine has been found in several interesting places. It appears to have landed in a meteorite and in the atmosphere of Venus.
Of particular interest is its presence in the atmosphere of comet 67P / Churyumov-Gerasimenko, suggesting that the molecule can form independently of the Sun or planets.
But laboratory experiments and modeling suggest that glycine is formed when interstellar ice is bathed in radiation ̵
At high enough energies, radiation can destroy amino acids, so a team of astronomers led by astrochemist Sergio Joopolo of Queen Mary University in London in the UK set out to see if there were alternative pathways.
And they found one.
“In the lab,” Joppolo said, “we were able to simulate conditions in dark interstellar clouds, in which cold dust particles are covered with thin layers of ice and subsequently treated by exposure to atoms, causing precursors to fragment and reactive intermediates to recombine.” .
The study began with methylamine, an amine precursor to glycine.
Although we have no evidence of the presence of glycine in the interstellar medium, astronomers have discovered methylamine – and methylamine has also been found on comet 67P / CG. In an independent set of experiments, the researchers showed that methylamine can be formed non-energetically in interstellar conditions.
The researchers then used methylamine-enriched ice to determine if glycine could form under similar conditions.
They deposited this in the form of a gas in an ultra-high vacuum system called SURFRESIDE2, designed specifically to study surface reactions in interstellar space. The system was cooled to an interstellar temperature of 13 Kelvin (-260 degrees Celsius, or -436 degrees Fahrenheit) to allow ice to form.
Chemical reactions in the ice have indeed led to the formation of glycine, the researchers found. And this ice was essential to the process.
They then used astrochemical modeling to confirm their findings. They extrapolated their experimental results, obtained in just one day, to the millions of years that cosmic processes can continue. And they found that glycine must be able to form in interstellar space, in small but significant amounts, in sufficient time.
These molecules are unlikely to evolve much further toward life in the cold-cold vacuum.
What the study means is that glycine and methylamine can form in space before star formation (and subsequent planet formation) begins. Which in turn means that there are potentially many prebiotic molecular materials trapped in the ice, which then accumulate on meteorites, comets, planetesimals and eventually planets.
“Once formed, glycine can become a precursor to other complex organic molecules,” Yopolo said.
“Following the same mechanism, other functional groups can generally be added to the glycine skeleton, leading to the formation of other amino acids, such as alanine and serine in dark clouds in space. Ultimately, this enriched organic molecular inventory is incorporated into celestial bodies, like comets, and delivered to young planets, as happened on our Earth and many other planets. “
The study was published in Natural astronomy.