In the early solar system, micrometeorites from icy bodies in the outer solar system may have been responsible for transporting nitrogen to the near-Earth region. The discovery was published in the journal Nature Astronomy by an international team of researchers, including scientists from the University of Hawaii Mānoa, led by Kyoto University.
Nitrogen compounds, such as ammonium salts, are abundant in materials produced far from the Sun, but little evidence of their transport to Earth's orbital regions is known.
Our recent findings suggest that there may be more nitrogen compounds being transported to the vicinity of Earth than previously recognized, potentially becoming the building blocks of life on our planet," said Hope Ishii, co-author of the study and affiliated faculty member of the Hawaii Institute of Geophysics and Planetology at the Mānoa School of Marine and Geosciences and Technology (SOEST).
The article, titled "Iron Nitride in Ryukyu Samples Indicates Influx of Nitrogen-Rich Materials from Outer Solar System," was published in the journal Nature Astronomy.
Like all asteroids, Ryugu is a small rocky body 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 interesting asteroid is rich in carbon and has undergone significant space weathering caused by micrometeorite collisions and exposure to currents of charged ions from the Sun.
In this study, the scientists aim to uncover clues about material reaching near Earth's orbit by examining evidence of space weathering in Ryukyu samples, which is currently located near Earth's orbit. Through electron microscopy, they found that the surface of the Ryukyu sample was covered with a tiny mineral composed of iron and nitrogen (ferric nitride: Fe4N).
Toru Matsumoto, the study's lead author and assistant professor at Kyoto University, said: "We propose that tiny meteorites containing ammonia compounds, called micrometeorites, came from an icy celestial body and collided with Ryugu. "Micrometeorite collisions triggered a chemical reaction on the magnetite that led to the formation of iron nitride. ”
Iron nitride is observed on the surface of magnetite consisting of iron atoms and oxygen atoms. When magnetite is exposed to the space environment, oxygen atoms disappear from the surface due to the irradiation of solar hydrogen ions (solar wind) and heating from micrometeorite impacts. These processes form metallic iron on the surface of the magnetite, which reacts readily with ammonia, creating ideal conditions for the synthesis of iron nitride.