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Molecule Smasher

Cosmic rays disintegrate formic acid—a possible precursor of biological compounds

ABIUROFormic acid, which is abundant in the regions of space where stars form, as well as in comets and small celestial bodies in the solar system, is considered to be a possible precursor of molecules that are essential to life. Physicists and biologists believe that when it interacts with nitrogen sources such as molecules of ammonia, it could play a role in the formation of glycine—the simplest amino acid and one of the chemical compounds that make up the proteins found in all living creatures. But no one knows for sure if formic acid molecules would survive in space long enough to combine with nitrogen sources and form amino acids. If they are unprotected, the answer appears to be no. A collaborative study by Brazilian and French researchers published in 2014 in the journal Monthly Notices of the Royal Astronomical Society indicates that formic acid cannot withstand the direct action of cosmic rays. In tests that simulated the conditions found in space, formic acid was degraded in water (H2O), carbon monoxide (CO) and carbon dioxide (CO2). More important than the absence of larger molecules, the experiment indicates that, under these conditions, it does not survive to enter into reactions with other substances.

Alexandre Bergantini, an astrophysicist doing research at Vale do Paraíba University (Univap) and principal author of the paper, says that the study simulated what would happen if, over a two-million- year period and with water present, cosmic rays were to bombard these small molecules residing on dust grains up to one micrometer in size, “smaller than the smallest grain of dust found on Earth,” the researcher explains. In the experiment, conducted at the National Large Heavy Ion Accelerator (GANIL) in Caen, France, Bergantini placed samples of formic acid with water into a stainless steel chamber—from which a special apparatus draws out all the air in a process that can take as much as a week to create an ultra-high vacuum at very low temperatures, around -260 degrees Celsius (°C)—and bombarded them with heavy ions, such as nickel, that travel across the Universe at very high speeds, thus simulating the action of cosmic rays. “Few particle accelerators work with such heavy ions,” Bergantini explains in justification of the partnership created for the study. In Brazil, it would not have been possible to do the experiments.

The study by the Univap group is derivative of the famous experiment performed by American scientists Stanley Miller and Harold Urey in the 1950s. They subjected water, methane, ammonia and hydrogen to electrical discharges inside a sealed apparatus, watched for several days as the liquid changed color, and confirmed the formation of amino acids such as glycine, as well as other organic compounds. That experiment, which showed that molecules which are the building blocks of life can originate from inorganic substances in extreme conditions, has given rise to a present-day field of research with instruments that have a precision probably unimaginable to Miller and Urey, who had worked with an indeterminate quantity of those elements and observed what happened using only the naked eye. “Our experiments are done on a nanometric scale, using one or two molecules and precisely measured and controlled radiation exposure, Bergantini explains. Immediately following the reactions, spectrometry enables scientists to detect the exact number and type of molecules that formed.

In their efforts to get a closer look at the possible trajectory of formic acid in space, the Brazilians obtained results that were somewhat surprising. “We thought the water would serve as a shield, but in fact it helped destroy the formic acid,” Bergantini says. And that is likely to be the most common scenario, since there is water throughout space. But it may not be that easy to degrade formic acid molecules in this way. This is because in the clouds where it is most abundant, formic acid may be more protected by the matter within the clouds and may not be destroyed so quickly—which would give it more time to react with compounds containing nitrogen and thereby create biotic molecules.

Space laboratory
To understand how the chemical evolution of the Universe occurs and gives rise to life, astronomer Sergio Pilling, Bergantini’s thesis advisor, established the Astrochemistry and Astrobiology Laboratory (LASA) over the past year at Univap, funded in large part by FAPESP under the Young Investigators program. “We can simultaneously simulate the effects of ultraviolet photons and electrons in the solar wind to more faithfully reproduce certain space phenomena,” Pilling says. “We can even achieve temperatures of ‑263°C and simulate the effect of space radiation on samples of interest for aerospace and aeronautics research.” Additional funding to maintain the laboratory comes from the National Council for Scientific and Technological Development (CNPq), the Brazilian Innovation Agency (Finep) and Univap.

Other studies conducted at the recently-installed laboratory in São José dos Campos have been yielding different results when formic acid and acetic acid are exposed to ultraviolet light and X-rays, to simulate the energy emitted by the Sun and other sources. “We are seeing other molecules forming besides the most obvious ones like CO2,” Bergantini adds in reference to findings that are still preliminary.

The National Aeronautics and Space Administration (NASA) recently announced that it expects to confirm within the next 20 years whether there is life in the Universe beyond Earth. Pilling agrees with that estimate. “I think mankind is very close to that type of finding,” he says. Using simulations done at LASA, he plans to contribute to the effort, also through analysis of samples collected by space probes that have landed on celestial bodies, or material collected from meteorites that fall to Earth, or through signals detected by radiotelescopes. “Our research is focused on finding more clues to the formation and origin of life by simulating space environments amenable to the formation of pre-biotic molecules such as amino acids and nitrogen bases that are essential to life as we know it.”

Synthesis and degradation of prebiotic molecular species at planetary atmospheres, comets and interstellar ice analogs (nº 09/18304-0); Grant mechanism Young Investigators; Principal investigator Sergio Pilling (Univap); Investment R$459,004.82 (FAPESP).

Scientific article
BERGANTINI, A. et alProcessing of formic acid-containing ice by heavy and energetic cosmic ray analoguesMonthly Notices of the Royal Astronomical Society. v. 437, n. 3, p. 2.720-27. 21 jan. 2014.