Analysis reveals that organic compounds found in asteroids likely formed in colder regions of space.

Analysis of organic compounds – called polycyclic aromatic hydrocarbons (PAHs) – extracted from the asteroid Ryugu and the Murchison meteorite revealed that some PAHs likely formed in the cold areas of space between stars rather than in the hot regions close to stars, as previously thought. The results open new possibilities for studying life beyond Earth and the chemistry of objects in space.

The only Australian members of an international research team, scientists from the WA-Organic and Isotope Geochemistry Center (WA-OIGC) in Curtin carried out controlled burning of plants to produce PAHs.

Their research paper, titled “Polycyclic aromatic hydrocarbons in Ryugu samples formed in the interstellar medium,” was published in the journal Science.

ARC Laureate Distinguished Professor Kliti Grice, WA-OIGC Director John Curtin said PAHs are organic compounds composed of carbon and hydrogen that are common on Earth, but are also found in celestial bodies such as asteroids and meteorites.

“We carried out controlled burning experiments on Australian plants, which were isotopically compared to PAHs from fragments of the asteroid Ryugu returned to Earth by a Japanese spacecraft in 2020, and from the Murchison meteorite which landed in Australia in 1969. “The links between light and heavy carbon isotopes present in PAHs were analyzed to reveal the temperature at which they formed,” Professor Grice said.

“Some PAHs from Ryugu and Murchison were found to have different characteristics: the smaller ones probably in cold space, while the larger ones probably formed in warmer environments, such as near a star or inside of a celestial body.”

Study co-author Dr Alex Holman, also from WA-OIGC, said understanding the isotopic composition of PAHs helps to understand the conditions and environments in which these molecules were created, providing insight into the history and chemistry of celestial bodies such as asteroids and meteorites.

“This research gives us valuable information about how organic compounds form beyond Earth and how they originate in space,” Dr Holman said.

“Using high-tech methods and creative experiments has shown that some PAHs on asteroids can form in cold space.”