Meteorites are likely a source of nitrogen for early Earth, study of samples from Ryugu finds

Micrometeorites from icy celestial bodies in the outer solar system may be responsible for transporting nitrogen to the near-Earth region in the early days of our solar system. This discovery was published in Natural astronomy by an international team of researchers, including scientists from the University of Hawaii at Mānoa, led by Kyoto University.

Nitrogen compounds, such as ammonium salts, are abundant in materials born in regions far from the sun, but evidence for their transport to Earth’s orbital region was poorly understood.

“Our recent findings suggest the possibility that a greater quantity of nitrogen compounds than previously recognized was transported near Earth, possibly providing a basis for life on our planet,” says Hope Ishii, co-author of the paper. study and affiliated professor at the University of Hawaii. UH Mānoa School of Ocean and Earth Science and Technology (SOEST) Institute of Geophysics and Planetology.

The paper titled “Influx of nitrogen-rich material from the outer solar system indicated by iron nitride in samples from Ryugu” was published in the journal Natural astronomy.

Like all asteroids, Ryugu is a small rocky object that orbits the sun. The Japan Aerospace Exploration Agency’s Hayabusa2 spacecraft explored Ryugu and brought material from its surface back to Earth in 2020. This intriguing asteroid is rich in carbon and has undergone significant spatial alteration caused by micrometeorite collisions and a exposure to charged ions from the sun.

In this study, scientists aimed to uncover clues about materials arriving near Earth’s orbit, where Ryugu is currently located, by examining evidence of spatial weathering in Ryugu’s samples. Using an electron microscope, they found that the surfaces of the Ryugu samples are covered in tiny minerals composed of iron and nitrogen (iron nitride: Fe₄NOT).

“We proposed that tiny meteorites, called micrometeorites, containing ammonia compounds were emitted from icy celestial bodies and collided with Ryugu,” said Toru Matsumoto, lead author of the study and assistant professor at Kyoto University. “Micrometeorite collisions trigger chemical reactions on magnetite and lead to the formation of iron nitride.”

Iron nitride has been observed on the surface of magnetite, which consists of iron and oxygen atoms. When magnetite is exposed to the space environment, oxygen atoms are lost from the surface by irradiation of hydrogen ions from the sun (solar wind) and by heating due to the impact of micrometeorites. These processes form metallic iron on the surface of the magnetite itself, which reacts readily with ammonia, creating ideal conditions for the synthesis of iron nitride.