Are some PAHs produced in low-temperature environments below -170°C? Contrary to the traditional view | sorae website portal to the universe

Less than 20% of the carbon compounds found in outer space are presentPolycyclic aromatic hydrocarbonsIt exists in the form of a compound called “(PAHs)'' which contains multiple benzene rings linked together. Although there is some debate about their origin, it is generally believed that they formed in a high-temperature environment such as near a star.

A research team including Sarah S. discovered Zeichner of the California Institute of Technology said that the asteroid'Ryugu“And the”Murchison meteoriteWe analyzed the PAHs present in each sample and estimated the environment in which they were manufactured. Results,Small molecular size PAHs are produced in low temperature environments below -170°C (100 K)We have found evidence that the virus was created in an environment that contradicts conventional thinking. On the other hand, since it has been shown that macromolecules form in high-temperature environments, this will have implications for the study of the formation of organic compounds in space.

■ Polycyclic aromatic hydrocarbons, carbon compounds that attract attention

It can be said that living organisms are a collection of complex organic compounds, so the answer to the question “What types of organic compounds are produced in the universe and in what environments?” It is important in terms of exploring the origin of life.

Among the organic compounds that attract attention are:Polycyclic aromatic hydrocarbons“There. This is a molecule consisting of multiple benzene rings connected in a regular hexagon of six carbon atoms. The reaction is thought to occur naturally when polycyclic aromatic hydrocarbons are combined with other elements such as oxygen and nitrogen to produce amino acids, the building blocks of proteins, and nucleotides, the building blocks Essential to DNA. For this reason, polycyclic aromatic hydrocarbons (PAHs) attract attention as precursors to the complex organic compounds that form the basis of life.

On the other hand, the mechanism by which PAHs, which are relatively complex molecules, are produced is not well understood. Observations show that PAHs make up less than 20% of the carbon compounds in the universe, so it is important to know the environment in which chemical reactions occur. In previous research, the theory was that it forms in the environment surrounding the star, where the temperature is above 1,300 °C (1,000 K), but the possibility that the reaction could continue in a lower-temperature environment is also being considered, and there is still debate that it was In a certain case.

■PAHs from Ryugu and the Murchison meteorite were produced in low-temperature environments.

In order to explore the origin of PAHs in the universe, Zeichner and his team investigated the origin of PAHs in an asteroid.Ryugu“And the”Murchison meteoriteWe analyzed the PAHs present in each sample. The Ryugu sample was brought to Earth by the Japan Aerospace Exploration Agency's Hayabusa2 spacecraft in 2020, and the Murchison meteorite is a meteorite that fell to Earth in 1969. What these samples have in common is that they contain extremely large amounts of carbon compounds, and have undergone little change since The birth of the solar system, containing materials before the birth of the solar system (pre-solar system material).

To understand the PAH production environment, it is necessary to examine the carbon isotope ratio. Isotopes are atoms that are chemically classified as the same element but have slightly different weights. Differences in weight also affect the ease with which atoms can move due to physical and chemical changes, so based on differences in isotope ratios, we can learn about differences in the environment such as the temperature at which the molecule was created.

Zeichner and his colleagues analyzed the isotope ratios of polycyclic aromatic hydrocarbons found in the Ryugu and Murchison meteorites, and studied the environment in which each type of molecule was produced. As a result, relatively low-molecular PAHs such as naphthalene, fluoranthene and pyrene were found to contain many heavy carbon atoms (carbon 13). There is a maximum deviation of 5.1% compared to the model that assumes that many heavy carbon atoms are included by chance, regardless of the production environment, so it is reasonable to believe that this difference is due to temperature. The results of this analysis are:Small PAHs below -170°Clike the interstellar medium between the stars.This indicates that it was produced in a fairly low temperature environment.. This result contradicts conventional thinking. On the other hand, the results showed that relatively high-molecular PAHs such as phenanthrene and anthracene were produced in high-temperature environments, which is consistent with conventional thinking.

The results of this analysis indicate that there are still aspects of PAH production in the universe that are not well understood. This research also shows that the low-molecular PAHs found in the Ryugu and Murchison meteorite formed before the birth of the solar system, which is another interesting discovery.

source

• Sarah S. Zeichner, et al. “Polycyclic aromatic hydrocarbons in samples from Ryugu formed in the interstellar medium.” (Sciences)
• Lucian Wilkinson. “Organic compounds in asteroids formed in cold regions of space: a study”. (Curtin University)

Written by Riri Aya