Polycyclic aromatic hydrocarbons (PAHs) contain ≲20% of the carbon in the interstellar medium. They are potentially produced in circumstellar environments by interstellar clouds or by processing of carbon-rich dust grains.
Scientists studied certain organic compounds, known as polycyclic aromatic hydrocarbons (PAHs), extracted from the Ryugu asteroid and Murchison meteorite. Surprisingly, they discovered these PAHs likely formed in the cold areas of space between stars rather than in hot regions near stars, challenging previous beliefs. This finding has opened up new possibilities for understanding life beyond Earth and the chemistry of celestial objects. The researchers from Curtin University in Australia conducted controlled burnings of plants to produce PAHs as part of this study.
ARC Laureate Fellow John Curtin Distinguished Professor Kliti Grice, director of WA-OIGC, said PAHs are organic compounds of carbon and hydrogen common on Earth but also found in celestial bodies like asteroids and meteorites.
“We performed controlled burn experiments on Australian plants, which were isotopically compared to PAHs from fragments of the Ryugu asteroid that were returned to Earth by a Japanese spacecraft in 2020 and the Murchison meteorite that landed in Australia in 1969. The bonds between light and heavy carbon isotopes in the PAHs were analyzed to reveal the temperature at which they were formed,” Professor Grice said.
“Select PAHs from Ryugu and Murchison were found to have different characteristics: the smaller ones likely formed in cold outer space, while bigger ones probably formed in warmer environments, like near a star or inside a celestial body.”
Study co-author Dr Alex Holman, also from WA-OIGC, said understanding the isotopic composition of PAHs helps unravel the conditions and environments in which these molecules were created, offering insights into the history and chemistry of celestial bodies like asteroids and meteorites.
“This research gives us valuable insights into how organic compounds form beyond Earth and where they come from in space,” Dr Holman said.
“The use of high-tech methods and creative experiments has shown that select PAHs on asteroids can be formed in cold space.”
Journal Reference:
- Sarah Zeichner, Jose Aponte et al. Polycyclic aromatic hydrocarbons in samples of Ryugu formed in the interstellar medium. Science. DOI: 10.1126/science.adg6304