One more step to understand the chemical complexity of the universe


Entrance of the Laboratory for the Simulation of Interstellar and Planetary Environments of the Center for Astrobiology and one of the simulation chambers it houses: ISAC (Interstellar Astrochemistry Chamber). Credit: CAB

Through simulation experiments radiating X-ray ices, an international scientific team, with the participation of the Center for Astrobiology (CAB), has managed to synthesize the molecules detected in protoplanetary disks and explain why it is not common to detect complex organic molecules in them. Understanding the production of these organic compounds in the early stages of star formation is critical to how evolution occurs from simple molecules to potentially life-carrying chemistry.

Currently, more than 200 molecules have been detected in the tenuous gas of the interstellar environment. Many of these molecules are organic and, thanks to laboratory experiments such as those conducted at the Astrobiology Center, they have been shown to form mainly in simple molecular ices that coat powder grains in dark interstellar regions.

Current technology, such as the ALMA Telescope (Atacama Large Milimeter Array), has allowed scientists to detect some of these molecules in protoplanetary disks, which often evolve into solar systems similar to ours. In particular, ALMA has detected on numerous occasions species such as CO, CO2, HCO and H2CO in the colder areas of the discs. However, others such as CH3OH or CH3CN have rarely been detected. And in the case of other complex organic molecules (COMs), essential for the onset of life, have not been detected at the moment in protoplanetary discs, but in some comets.

In order to explain why these molecules have not been detected in protoplanetary disks, an international team with the participation of the Center for Astrobiology, has conducted different simulation experiments in the laboratory. To do this, researchers have simulated ice processing on protoplanetary disks. "We created a more realistic ice with a structure similar to those observed in space," explains Guillermo M. Muñoz Caro, CAB researcher and co-author of the study recently published in the journal PNAS. "We generate an ice composed of two layers and then irradiate it with soft X-rays, such as those emitted by young solar-type stars, using NSSRC (Taiwan) synchrotron light as an X-ray source," he adds. 

Ice molecules are often broken down by the effect of radiation and fragments that form can lead to new chemical species. Thanks to these types of experiments, scientists have discovered that all molecules that escaped ice during irradiation (both initial and radiation-formed) match those detected in the gas of protoplanetary discs. However, it was observed that complex organic molecules, on the other hand, remained in the ice during irradiation and the ice needed to be heated for it to go into the gas phase. "This would explain why complex organic molecules have not yet been observed in protoplanetary discs, as ice in these areas are at low temperatures."

These results could also explain the presence of COMs in some comets, such as 67P, which are close enough to the Sun to allow these molecules to escape from the ice and be detected in the gas phase. "It is to be hoped that the contribution of this organic matter to Earth, from comets and asteroids, provided a favorable environment for life to emerge," says Guillermo M. Muñoz Caro.


Fuente: UCC-CAB

Fecha: 2020-07-17


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