In 2014 the Rosetta space probe reached a comet that is orbiting in our solar system. A small lander vehicle detected the presence of glycine on the comet, an unexpected discovery as the glycine molecule is an amino acid. Amino acids form the basis for proteins, and are an essential element of all life on earth. But how did these amino acids come to be present on earth?

Piggybacking on meteorites

'The discovery of glycine on the comet seems to indicate that amino acids are formed in space,' comments PhD candidate Daniël Paardekooper. 'It seems likely that these amino acids are able to enrich planetary biological matter by piggy-backing on meteorites.' Paardekooper set up a lab experiment in the Sackler Laboratory for Astrophysics to study this hypothesis.

Complex molecules

Paardekooper looked specifically at the conditions that are prevalent in dark instellar nebulae. Nebulae are clouds of gas, plasma and cold matter that occur in all galaxies. After millions of years, ice crusts form on these particles. The ice consists not only of water, but also of other frozen components, such as methane and methanol. These molecules can disintegrate if they are irradiated by high-energy light particles -- and there are plenty of these in space. Once they have disintegrated, the fragments interreact with one another and form larger and more complex molecules.

Fats and sugars

Paardekooper shows in his lab study that chemical reactions between separate particles can indeed take place on icy surfaces, comparable with the extreme circumstances in dark clouds. Paardekooper was able to produce fats and sugars in his experimental set-up. The expectation is that even more complex amino acids can originate on icy dust particles, although Paardekooper did not manage this last step. 'That will be the subject of my successor's dissertation.'

Unanswered

This does not confirm the hypothesis that amino acids reach the earth via comets and meteorites. There are questions that still have to be answered, such as whether they are able to survive a journey through the earth's atmosphere, or a crash landing on the earth's surface. Paardekooper: 'Somehow or other, the building blocks of life are present throughout the universe. That makes it more likely that other planets also meet the conditions for the origin of life.'

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