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Telltale chemistry could betray ET
NASA/JPL/Cornell
THIS WEEK fundamental to terrestrial life. Adami found a similar signature for carboxylic acids, which include common substances like formic acid. Lifeless samples were dominated by small acids up to six carbon atoms long, while biological samples contained acids up to 30 carbon atoms long, with a preference for even-numbered chains. Adami then went a step further. Since 1993 he has worked with Avida, a computer system in which programs called avidians compete for processing power. Each avidian is an artificial organism, built from a set of 29 simple instructions analogous –Mars may yet show signs of life– to the 20 amino acids found in terrestrial life and able to evolve through mutation and selection. of the Keck Graduate Institute of If the organisms were absent Applied Life Sciences in Claremont, each of the instructions would California, and colleagues pulled be equally abundant. But when together 30 measurements of Adami ran 350 populations of amino acid abundances from avidians under a range of abiotic sources, including conditions, he found that certain meteorites and lab synthesis Identifying the alien equivalents experiments, and compared them instructions always became more of those chemical building with 125 samples taken from soils, abundant at the expense of blocks “is our only way to detect others, creating an avidian ocean sediments and water. life not as we know it”, says “chemical” signature that The lifeless samples were astrobiologist Chris McKay of indicated their presence (Journal dominated by the simplest NASA’s Ames Research Center in of Molecular Evolution, in press). amino acids, glycine and Moffett Field, California. He calls “That’s very important,” says alanine. In contrast, the biological this the Lego principle. McKay. “What we see on Earth sources also had plenty of the To test the idea, Christoph Adami more complicated amino acids is not a quirk of Earth biology but a universal principle.” That may be true, says Dirk The search for alien lego Schulze-Makuch of Washington No Mars mission has yet tried to molecules including DNA and sugars. State University in Pullman, but detect life using the Lego principle In work yet to be published, he warns chemical ET hunters that (see main story), but similar methods Parro found that SOLID2 successfully different minerals, temperatures are being investigated. detected life in two largely lifeless and pressures could allow for The team behind the ExoMars environments – Antarctica during chemical reactions that do not rover, scheduled for launch in 2018, winter, and the height of summer occur on Earth. So determining plans to look for amino acids that in the Atacama desert. He is now whether the recorded abundances have the same symmetry as each exploring ways to get it flown to Mars. represent abiotic baseline other. All Earth life is based on amino According to Christoph Adami conditions or the presence of life acids of the same symmetry, so this of the Keck Graduate Institute, might prove tricky. “There’s a lot could be a telltale sign – assuming SOLID2 is too Earth-centric, because of uncertainty,” he says. Martian life uses amino acids at all. it looks for specific sequences of Adami agrees that it is a Victor Parro of the Centre for molecules. “They are looking for challenge, but thinks it is not Astrobiology in Madrid, Spain, and his phrases like ‘I think therefore I am’, an insuperable one. “You would colleagues have a different approach. whereas I am looking for the have to establish the geochemistry Rather than staking everything on frequencies of individual letters,” he well enough to know what the one type of molecule, their device, says. Still, he thinks the technology ‘alphabet’ of molecules was” SOLID2, can detect a wide range of could be modified to fit this purpose. before hunting for unusual relative abundances, he says. n
Telltale chemistry could betray ET Michael Marshall
ALIEN life might be hard to find for the simple reason that it is fundamentally unlike Earth life. It might not use DNA, or contain protein. But whatever and wherever it is, its tendency to chemically alter its environment might just give it away. Life has had a radical impact on Earth’s chemistry – perhaps most notably leading to soaring atmospheric oxygen concentrations around 2.2 billion years ago. If life
“The chemical signatures we see on Earth are not a quirk of Earth biology but a universal principle” has had a comparable impact elsewhere in the solar system, the relative abundances of chemicals key for its survival – whatever they may be – could betray its presence. On Earth, those key chemicals, such as amino acids, are modestly sized, exist in relatively small numbers and act as building blocks to form all complex life. 10 | NewScientist | 22 January 2011
THIS WEEK fundamental to terrestrial life. Adami found a similar signature for carboxylic acids, which include common substances like formic acid. Lifeless samples were dominated by small acids up to six carbon atoms long, while biological samples contained acids up to 30 carbon atoms long, with a preference for even-numbered chains. Adami then went a step further. Since 1993 he has worked with Avida, a computer system in which programs called avidians compete for processing power. Each avidian is an artificial organism, built from a set of 29 simple instructions analogous –Mars may yet show signs of life– to the 20 amino acids found in terrestrial life and able to evolve through mutation and selection. of the Keck Graduate Institute of If the organisms were absent Applied Life Sciences in Claremont, each of the instructions would California, and colleagues pulled be equally abundant. But when together 30 measurements of Adami ran 350 populations of amino acid abundances from avidians under a range of abiotic sources, including conditions, he found that certain meteorites and lab synthesis Identifying the alien equivalents experiments, and compared them instructions always became more of those chemical building with 125 samples taken from soils, abundant at the expense of blocks “is our only way to detect others, creating an avidian ocean sediments and water. life not as we know it”, says “chemical” signature that The lifeless samples were astrobiologist Chris McKay of indicated their presence (Journal dominated by the simplest NASA’s Ames Research Center in of Molecular Evolution, in press). amino acids, glycine and Moffett Field, California. He calls “That’s very important,” says alanine. In contrast, the biological this the Lego principle. McKay. “What we see on Earth sources also had plenty of the To test the idea, Christoph Adami more complicated amino acids is not a quirk of Earth biology but a universal principle.” That may be true, says Dirk The search for alien lego Schulze-Makuch of Washington No Mars mission has yet tried to molecules including DNA and sugars. State University in Pullman, but detect life using the Lego principle In work yet to be published, he warns chemical ET hunters that (see main story), but similar methods Parro found that SOLID2 successfully different minerals, temperatures are being investigated. detected life in two largely lifeless and pressures could allow for The team behind the ExoMars environments – Antarctica during chemical reactions that do not rover, scheduled for launch in 2018, winter, and the height of summer occur on Earth. So determining plans to look for amino acids that in the Atacama desert. He is now whether the recorded abundances have the same symmetry as each exploring ways to get it flown to Mars. represent abiotic baseline other. All Earth life is based on amino According to Christoph Adami conditions or the presence of life acids of the same symmetry, so this of the Keck Graduate Institute, might prove tricky. “There’s a lot could be a telltale sign – assuming SOLID2 is too Earth-centric, because of uncertainty,” he says. Martian life uses amino acids at all. it looks for specific sequences of Adami agrees that it is a Victor Parro of the Centre for molecules. “They are looking for challenge, but thinks it is not Astrobiology in Madrid, Spain, and his phrases like ‘I think therefore I am’, an insuperable one. “You would colleagues have a different approach. whereas I am looking for the have to establish the geochemistry Rather than staking everything on frequencies of individual letters,” he well enough to know what the one type of molecule, their device, says. Still, he thinks the technology ‘alphabet’ of molecules was” SOLID2, can detect a wide range of could be modified to fit this purpose. before hunting for unusual relative abundances, he says. n
Telltale chemistry could betray ET Michael Marshall
ALIEN life might be hard to find for the simple reason that it is fundamentally unlike Earth life. It might not use DNA, or contain protein. But whatever and wherever it is, its tendency to chemically alter its environment might just give it away. Life has had a radical impact on Earth’s chemistry – perhaps most notably leading to soaring atmospheric oxygen concentrations around 2.2 billion years ago. If life
“The chemical signatures we see on Earth are not a quirk of Earth biology but a universal principle” has had a comparable impact elsewhere in the solar system, the relative abundances of chemicals key for its survival – whatever they may be – could betray its presence. On Earth, those key chemicals, such as amino acids, are modestly sized, exist in relatively small numbers and act as building blocks to form all complex life. 10 | NewScientist | 22 January 2011