Through the incineration of Australian plants, scientists have learned that certain molecules present in asteroids and meteorites originated in the frigid interstellar medium, eons before the Sun.
Numerous intriguing molecules were discovered in the samples that Hayabusa-2 brought back to Earth from the surface and interior of the asteroid Ryugu three years ago. Polycyclic aromatic hydrocarbons (PAHs) are one type of them.
One well-known PAH is naphthalene, which is found in mothballs. However, numerous others can be found in coal, oil, natural gas, and burned organic matter. They are available in a wide variety of shapes and sizes. Researchers contrasted examples produced by burning plants with PAHs discovered in Ryugu and the meteorite that crashed into Earth fifty years ago, known as the Murchison meteorite.
They were specifically contrasting isotopes, which are various forms of the same element. Isotopes differ in the amount of neutrons in their nuclei, which causes them to be slightly heavier or lighter despite sharing the same chemical characteristics. The rarer isotopes are typically radioactive as well. For instance, there are different isotopes of carbon. The most prevalent is called carbon-12, but carbon-13 and carbon-14 can also be found in nature.
“We conducted controlled burn experiments on Australian plants, and the results were isotopically compared to PAHs from the 1969 Australian meteorite strike Murchison and pieces of the Ryugu asteroid that were brought back to Earth by a Japanese spacecraft in 2020. The temperature at which the PAHs were formed was determined by analyzing the bonds between the light and heavy carbon isotopes in the compounds, according to a statement released by Curtin University professor Kliti Grice, a co-author.
The scientists discovered that the isotopes in the most basic, lighter PAHs from space, such as naphthalene, had to have formed thousands of degrees below freezing, far from stars and solid bodies. That was before the Sun rose. However, a few of them—the larger ones—formed during the solar system’s formation.
“Select PAHs from Ryugu and Murchison were found to have different characteristics: the smaller ones likely in cold outer space, while bigger ones probably formed in warmer environments, like near a star or inside a celestial body,” said Professor Grice.
Since OSIRIS-REx returned with material from Bennu, there are even more asteroid samples on Earth. Scientists may be able to determine the origins of planets and life by using this type of analysis along with additional research.
Co-author Dr. Alex Holman, also of Curtin University, said, “This research gives us valuable insights into how organic compounds form beyond Earth and where they come from in space.” “The use of high-tech methods and creative experiments has shown that select PAHs on asteroids can be formed in cold space.”