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Seeds of life in space

Effect of cosmic rays may have generated molecules that formed animals and plants

DETAIL OF THE WORK THE DAY WE HIT THE MOON BY SHEILA GOLOBOROTKOParts of DNA and other essential molecules in living beings may have formed in space billions of years ago and got a ride to Earth on comets or meteorites. One hypothesis that has acquired new arguments is that the fragments of these molecules may have appeared in galactic clouds bombarded by cosmic rays, high-energy particles that have been abundant since the start of the Universe. Such clouds are extremely cold and consist of grains of solid water and condensed gases, such as carbon monoxide, carbon dioxide, ammonia and methane.

Brazilian and French physicists reached these conclusions through experiments in particle accelerators at PUC-Rio (the Catholic University of Rio de Janeiro) and at the University of Caen-Low Normandy, in Caen, northwest France. The ion beams produced in these machines interact with ice kept as cold as -260o Celsius, producing effects similar to those of cosmic rays upon galactic clouds.

“We’re rebuilding the conditions of the emergence of the earliest steps of life,” says the physicist Enio Silveira, from PUC-Rio. “We want to discover what results from sidereal space ice bombarded by cosmic rays.” According to him, the meeting of cosmic rays and ice clouds is akin to sandblasting a wall: the grains of sand erode the wall’s surface. Another possibility is that the organic molecules might have been formed from the interaction with another type of beam of elementary particles, the electrons. These are more abundant, but have less energy than the cosmic rays.

The experiments of the PUC-Rio and Caen teams indicated that the water can decompose and form hydrogen peroxide (H2O2), ozone (O3) or chemical radicals with a strong affinity for molecules with the opposite electrical charge. In 2009 and 2010, as part of his doctoral studies, the astronomer Eduardo Seperuelo Duarte, from PUC, worked for 18 months with Alicja Domaracka at Ganil (the Great National Accelerator of Heavy Ions) in Caen, to determine what new chemical species come out of the frozen clouds of carbon monoxide (CO) or carbon dioxide (CO2) bombarded by nickel ions. “Cosmic rays formed by elements with a high atomic mass, like nickel, are rare in the Universe, but their effect is devastating, like that of a cannon shot in a war, as compared to the far more plentiful machine-gun shots,” compares Silveira. In other Ganil tests held in December, the physicist Ana Lúcia Barros, from Silveira’s group, found that five different molecules, such as CH3 and C2H4, are formed in the methane(CH4) clouds bombarded by ion beans simulating cosmic rays.

“The cosmic rays may induce the synthesis of new molecules if ice cloud exposure to them is temporary,” comments Silveira. “Long-lasting bombarding hinders the formation of macromolecules.” In December of 2009, Alicja Domaracka visited Brazil and worked with Silveira at the PUC accelerator, bombarding lithium fluoride crystals, which shattered in a similar way to the ice clouds.

“Our planet was heavily bombarded by comets, which brought the water that forms part of the oceans,” states Silveira. “Life arose here in a relatively short time, only about 1 billion years after the Earth was formed.” If this hypothesis is correct, comets may have carried the organic molecules to any corner of the Universe, enhancing the possibility of extraterrestrial life.