Findings by astrobiologists at Imperial College suggest violent celestial impacts deliver building blocks for life to planets
Violent impacts from comets and other hurtling bodies can pepper planets and their moons with the molecular building blocks of life, new research suggests.
The high-speed collisions unleash intense shockwaves that can turn simple organic compounds found in comets and on icy worlds into amino acids, which make proteins, cells and ultimately all living organisms.
The findings suggest that rather than being a purely destructive force, the impacts increase the odds of life originating and being widespread across our solar system.
"We know that impacts are very common in the solar system, because we can see the craters left behind on different planetary bodies," said Zita Martins, an astrobiologist at Imperial College in London.
"If impacts occur then more complex molecules can be made, so these building blocks of life could be widespread throughout our solar system."
The surfaces of planets and moons are scarred from billions of years of violent impacts with space rocks left over from the birth of the solar system. The impacts release profound amounts of energy: the meteor that tore into the sky over Chelyabinsk in Russia this year arrived at more than 18 kilometres per second and exploded with 30 times the energy of the Hiroshima nuclear bomb.
Scientists have previously used computer models to demonstrate that shockwaves could turn simple molecules found in icy comets, such as ammonia, carbon dioxide and methanol, into complex amino acids. That work prompted researchers to test the idea by reconstructing celestial impacts in the laboratory.
Researchers at Imperial College and the University of Kent teamed up with Nir Goldman, a researcher at the US Lawrence Livermore National Laboratory, whose models showed that amino acids might be made in comet strikes. They made batches of ice mixture laced with ammonia, methanol and carbon dioxide to represent different compositions of comets. To mimic a comet's impact on a planet, they fired sterilised steel balls into half-kilogram lumps of each ice mixture using an instrument called a light gas gun.
After each shot, the scientists looked for traces of amino acids in the ice they had fired at and also in a block of the same ice mixture that had not been fired at. This second lump acted as a control to ensure that any amino acids they found had been created, and were not caused by contamination before or during the firing stage.
Writing in the journal Nature Geoscience, the researchers show that an impact at around seven kilometres per second produced scores of amino acids in one ice mixture. The impact creates an intense shockwave that fragments the simple compounds, which then recombine into amino acids, such as alanine and glycine. Among the numerous roles they play in life, glycine is a neurotransmitter that is active in the brain stem and retina, while alanine is found in bacterial cell walls.
"Although there are other chemical paths that can generate amino acids, the one we describe can occur during an impact, where no special conditions, such as UV radiation, are required, if the initial ingredients are present," said Mark Price, a co-author on the study at the University of Kent at Canterbury.
"The important implication is that the complex precursors to life, such as amino acids, are widespread, thus increasing the chances of life evolving elsewhere," he said.
The creation of amino acids through violent impacts is expected to happen not only when icy comets laced with simple compounds slam into rocky planets and moons, but when meteorites and other space rocks crash into icy surfaces, such as those found on Saturn's moon, Enceladus, and Jupiter's moon, Europa.
"What we have done is demonstrate a process that takes molecules that were present at the time of the birth of the solar system and made them into molecules that are required for life. It's like taking simple lego bricks and sticking two together. You are along way from building a house, but it is a start," said Price.
Charles Cockell, professor of astrobiology at Edinburgh University, said the work demonstrates that there are many ways to create amino acids, the components of proteins. "Although we once thought that the formation of the molecules required for life was highly improbable and rare, evidence increasingly suggests that they might be common throughout the universe. Of course the probability that they assemble into life is still unknown," he said.
guardian.co.uk © Guardian News and Media 2013
["Comet over desert" via NASA]