"Long before it's in the papers"
January 27, 2015


Life’s ingredients could form through cometary impact, study finds

Sept. 17, 2013
Courtesy of Liv­er­more Na­t­ional Lab­o­r­a­to­ry
and World Science staff

While past stud­ies have sug­gested a com­et could br­ing some in­gre­di­ents of life to Earth, new re­search claims some of those In­gre­di­ents could form as a re­sult of the com­et im­pact it­self.

To find out, sci­en­tists “shock-compressed” an icy mix­ture si­m­i­lar to what is found in com­ets. This led, they said, to the forma­t­ion of a num­ber of ami­no ac­id­s—the build­ing blocks of life. The re­search ap­peared in the ad­vance on­line is­sue of the jour­nal Na­ture Ge­o­sci­ence Sept. 15.

It’s an ex­pe­ri­men­tal con­firma­t­ion of re­cent pre­dic­tions by Nir Gold­man, a sci­ent­ist at the Law­rence Liv­er­more Na­t­ional Lab­o­r­a­to­ry. 

Used su­per­com­puter sim­ula­t­ions, Gold­man had found that the im­pact of icy com­ets crash­ing in­to Earth bil­lions of years ago could have pro­duced a va­ri­e­ty of “pre­bi­otic,” or life-build­ing, com­pounds. These would have in­clud­ed ami­no ac­ids, which are crit­i­cal to life and serve as the build­ing blocks of larg­er mo­le­cules used by liv­ing things—pro­teins. 

Gold­man’s work pre­dicted that the sim­ple mo­le­cules found in com­ets (such as wa­ter, am­mo­nia, meth­a­nol and car­bon di­ox­ide) could have sup­plied the raw ma­te­ri­als, and the im­pact with early Earth would have yielded an abun­dant supply of en­er­gy to drive this pre­bi­otic chem­is­try.

In the new work, col­la­bo­ra­tors from Im­pe­ri­al Col­lege Lon­don and the Uni­vers­ity of Kent in the U.K. con­ducted ex­pe­ri­ments si­m­i­lar to Gold­man’s sim­ula­t­ions, by firing a pro­jec­tile in­to a “typ­i­cal” com­etary ice mix­ture. Sev­er­al dif­fer­ent types of ami­no ac­ids formed, they said.

“The im­pact it­self can yield life-build­ing com­pounds,” Gold­man said. Comets are known to har­bor sim­ple ices and the or­gan­ic pre­cur­sors of ami­no ac­ids. Glycine—the sim­plest ami­no ac­id—was re­cently con­firmed to be in com­et Wild-2. Gold­man’s orig­i­nal work used sim­ula­t­ions of in­ter­ac­tions among mo­le­cules to show that shock waves pass­ing through com­et-like mix­tures, due to an im­pact, could trig­ger ami­no ac­id forma­t­ion. 

“These re­sults pre­s­ent a sig­nif­i­cant step for­ward in our un­der­stand­ing of the or­i­gin of the build­ing blocks of life,” Gold­man said.

The team found that icy bod­ies with the same com­pounds cre­at­ed from com­et im­pacts al­so might be found in the out­er so­lar sys­tem. For ex­am­ple, En­cel­a­dus, one of Sat­urn’s moons, con­tains a mix of light or­gan­ic com­pounds and wa­ter ice. The team con­clud­ed that a suf­fi­ciently fast-mov­ing com­et would probably im­part enough en­er­gy to pro­mote forma­t­ion of more com­plex or­gan­ic com­pounds, in­clud­ing ami­no ac­ids, from these ices. “This in­creases the chances of life or­i­ginating and be­ing wide­spread through­out our so­lar sys­tem,” Gold­man said.

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While past studies have suggested a comet could bring the ingredients of life to Earth, new research claims some of those Ingredients could form as a result of the comet impact itself. To find out, scientists “shock-compressed” an icy mixture similar to what is found in comets. This led, they said, to the formation of a number of amino acids—the building blocks of life. The research appeared in the advance online issue of the journal Nature Geoscience Sept. 15. It’s an experimental confirmation of recent predictions by Nir Goldman, a scientist at the Lawrence Livermore National Laboratory. Used supercomputer simulations, Goldman had found that the impact of icy comets crashing into Earth billions of years ago could have produced a variety of “prebiotic,” or life-building, compounds. These would have included amino acids, which are critical to life and serve as the building blocks of larger molecules used by living things—proteins. Goldman’s work predicted that the simple molecules found in comets (such as water, ammonia, methanol and carbon dioxide) could have supplied the raw materials, and the impact with early Earth would have yielded an abundant supply of energy to drive this prebiotic chemistry. In the new work, collaborators from Imperial College in London and University of Kent conducted a series of experiments very similar to Goldman’s previous simulations in which a projectile was fired using a light gas gun into a typical cometary ice mixture. The result: Several different types of amino acids formed, they said. “These results confirm our earlier predictions of impact synthesis of prebiotic material, where the impact itself can yield life-building compounds,” Goldman said. “Our work provides a realistic additional synthetic production pathway for the components of proteins in our solar system, expanding the inventory of locations where life could potentially originate.” Comets are known to harbor simple ices and the organic precursors of amino acids. Glycine—the simplest amino acid—was recently confirmed to be in comet Wild-2. Goldman’s original work used simulations of interactions among molecules to show that shock waves passing through comet-like mixtures, due to an impact, could trigger amino acid formation. “These results present a significant step forward in our understanding of the origin of the building blocks of life,” Goldman said. The team found that icy bodies with the same compounds created from comet impacts also might be found in the outer solar system. For example, Enceladus, one of Saturn’s moons, contains a mix of light organic compounds and water ice. The team concluded that a sufficiently fast-moving comet would probably impart enough energy to promote formation of more complex organic compounds, including amino acids, from these ices. “This increases the chances of life originating and being widespread throughout our solar system,” Goldman said.