Some of the key ingredients for life may have been shocked into existence. A physical simulation of a comet's impact with a planet shows that the conditions are extreme enough to create amino acids within the comet's ice.
Astrobiologists have long wondered whether life or its ingredients could have travelled to Earth on the back of a comet or asteroid. Comets are known to contain the organic precursors of amino acids, which are the building blocks of proteins.
What's more, one comet, Wild 2, was recently shown to contain the simplest amino acid, glycine. But how such an amino acid could form there is still a mystery.
"We do, however, know that high speed impacts are a ubiquitous process as we see impact craters on every solid surface in the solar system," says Mark Price at the University of Kent, UK.
Speeding pellet
Theoretical studies had suggested that the shock of an impact could rearrange the components of the ice into something more interesting.
"The idea is that a comet would contain the raw materials for life-building compounds," says Nir Goldman of Lawrence Livermore National Laboratory in California, who made the theoretical calculations. "When a comet impacts a planetary surface, it creates very high pressures and temperatures. Those will then drive the raw materials that already exist in the comet to form more complex things that could be life-building."
To find out if this works in practice, Price and colleagues made model comet ice in the lab containing various amounts of ammonia, carbon dioxide and methanol. Then they shot the ice with a steel pellet travelling at about 7 kilometres a second to simulate the comet smacking into a planet, or another body colliding with the comet.
When they evaporated the ice away, the remaining goop contained the amino acids alanine and norvaline.
"This is significant, as we now have a simple, realistic mechanism to generate amino acids," Price says. "As impacts between icy bodies occur throughout the solar system, then complex organic molecules are also, very probably, widespread."
"This is a neat way of suggesting prebiotic material could be produced regardless of the external conditions of the planet," says Goldman.
"You could have a planet that isn't really conducive to forming amino acids, like early Earth supposedly wasn't," he says. "But then you can have a comet come in, and that impact will drive prebiotic processes within the comet itself, regardless of what the planet looks like."
Journal reference: Nature Geoscience , DOI: 10.1038/ngeo1930
If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.
Have your say
Only subscribers may leave comments on this article. Please log in.
Only personal subscribers may leave comments on this article
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support.
