Amino acids formed when steel balls impacted an ice mixture

A crash of a comet (icy body) on rocky surfaces or rocky body on icy surface may be all that is required for seeding planets or satellites with amino acids — the basic building blocks so very essential for life. This was predicted using computer simulations in 2010 and 2013.

Though comets harbour the organic precursors — some kind of carbon like methane or carbon dioxide, a nitrogen source like ammonia and water ice — of amino acids, the conversion of the precursors to amino acids would happen only if the impact has a specific speed, and hence, a specific shock pressure.

A study published a few days ago in Nature Geoscience has for the first time experimentally produced amino acids by mimicking the impact of a rocky body on an icy surface. “Our impact-shock experiments support a revival of the hypothesis of the role of comets in exogenous delivery to the early earth,” notes Zita Martins from the Department of Earth Sciences and Engineering, Imperial College, London and the first author of the paper.

To mimic the way amino acids are produced by impacting comets, the researchers prepared several ice mixtures found on comets and shocked the mixtures by impacting them with 2 mm steel balls fired at high velocities. “Several amino acids, including linear and methyl alpha amino acids” were produced.

Detectable levels of amino acids were formed only when the ice contained a mixture of ammonium hydroxide, carbon dioxide and methanol in a certain ratio (9.1:8:1) and was impacted by steel balls at 7.15 kilometres per second and 7 kilometres per second speeds. These velocities produced a pressure of 50 gigapascal (500,000 bar). This is the “approximate pressure required for the dissociation and recombination of the ice molecules,” they write.

To make sure that it was only the impact of the steel balls that produced the amino acids, the researchers split a block of ice into two and only one was impacted with balls. No amino acids were seen in the control ice mixture that did not undergo shock synthesis. They also repeated the process a year later using freshly prepared ice mixtures with identical compositions as in the experiment carried out a year before.

Repeatability

The suite of amino acids produced was the same in both the ice mixtures impacted with steel balls. The only difference between the first experiment and the second was in the abundance of certain amino acids produced.

Since the alpha amino acid is produced by a two-step process, the initial composition of the ice — ammonia, carbon dioxide and methanol — is very important, they note. Another important observation has been the respective roles of impact shock and impact heating in the formation of alpha amino acids. They stress that impact shock (pressure) produced by the steel balls converts the ice mixture into amino acid precursors; the impact heating then changes the precursors into alpha amino acids.

“Our findings suggest a pathway for the synthetic production of the components of proteins within our Solar System, and thus a potential pathway towards life through icy impacts,” the write. Since many of the icy bodies in the Solar System have the compounds used in this study, the probability of amino acids being present is quite high, considering that these bodies are bombarded by comets.

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