Astronomers have discovered an unexpected number of different types of organic matter, namely complex carbon compounds, outside Earth. Most extraterrestrial organics are polycyclic aromatic hydrocarbons (PAHs), such as naphthalene, phenanthrene, and the like. The authors of the new study analyzed samples of the Murchison meteorite and the Ryugu asteroid and concluded that most of the PAHs in their composition appeared in low-temperature conditions, far from stars.

It has long been thought that organic compounds (those containing interconnected chains and rings of carbon atoms) are the product of chemical reactions in living things. This was fixed in their name, which is still used today. It later turned out that organic matter could form without the help of organisms. Moreover, there are many of them outside our planet and even outside the solar system. Astronomers have observed significant numbers of highly complex organic matter in space, including alcohols and individual components of DNA or proteins.

Authors of a new article in the journal Science He became interested in polycyclic aromatic hydrocarbons (PAHs), one of the classes of organic compounds found in space. They consist of only two chemical elements – hydrogen and carbon – that form condensed (directly adjacent) aromatic rings.

Surfactants account for up to 20 percent of the carbon in interstellar space; Here are found representatives of this group of substances, such as naphthalene (two condensed rings), anthracene (three consecutive rings) and pyrene, which consists of four condensed rings.

Astrochemists were interested in the conditions under which such compounds with highly complex structures arise. To this end, they examined the isotopic composition of carbon and hydrogen from samples of the Murchison meteorite (a carbonaceous chondrite that crashed in Australia in 1969) and samples of the near-Earth asteroid Ryugu obtained by the Japanese Hayabusa-2 probe. For comparative purposes, the composition of burnt plant remains is also described.

It was found that the isotopic composition of carbon in the surfactant composition of celestial bodies differs significantly from random. In the case of naphthalene, fluoranthene and pyrene from Ryug and fluoranthene from the Murchinson meteorite, deviations were estimated at 9-51 ppm. The study’s authors concluded that this complex organic matter may have formed under two very different conditions.

Most PAHs with two and four fused rings (naphthalene, pyrene, and fluoranthene) were probably formed at low temperatures (about 10 degrees Kelvin, or minus 263.15 degrees Celsius). This corresponds to cold regions very far from stars, that is, in interstellar space.

Meanwhile, it became clear that other PAHs (three-ring, anthracene, and phenanthrene) were synthesized or emerged during higher-temperature chemical transformations of other organic molecules. It may have occurred on a cosmic body near the star or orbiting it.