Scientists discover source of nitrogen in early solar system

A groundbreaking study published in Nature Astronomy by an international team led by Kyoto University, including scientists from the University of Hawai’i at Mānoa, reveals a potential cosmic delivery service of nitrogen compounds to the near-Earth region in the early stages of our solar system. Micrometeorites originating from icy celestial bodies in the outer solar system could be the carriers of nitrogen, a critical element for life.

Nitrogen compounds, specifically ammonium salts, are known to be prevalent in materials formed in regions distanced from the sun. However, the mechanism by which these compounds traverse to Earth’s orbital vicinity has been a puzzle until now.

Hope Ishii, study co-author and affiliate faculty at the Hawai’i Institute of Geophysics and Planetology in the UH Mānoa School of Ocean and Earth Science and Technology (SOEST), underscores the significance of their findings. “Our recent findings suggest the possibility that a greater amount of nitrogen compounds than previously recognized was transported near Earth, potentially serving as building blocks for life on our planet.”

The study, titled “Influx of nitrogen-rich material from the outer Solar System indicated by iron nitride in Ryugu samples,” and published in Nature Astronomy, leveraged data from the Japan Aerospace Exploration Agency’s Hayabusa2 mission, which explored the asteroid Ryugu and returned samples to Earth in 2020.

Ryugu, like other asteroids, is a small rocky object orbiting the sun. Rich in carbon and subjected to space weathering from micrometeorite collisions and solar ion exposure, Ryugu became a focal point for researchers aiming to unravel the mysteries of materials arriving near Earth’s orbit.

Using electron microscopy, the scientists discovered tiny minerals composed of iron and nitrogen (iron nitride: Fe4N) covering the surfaces of Ryugu samples. Toru Matsumoto, lead author of the study and assistant professor at Kyoto University, explained the role of micrometeorites in this process. “We proposed that tiny meteorites, called micrometeorites, containing ammonia compounds were delivered from icy celestial bodies and collided with Ryugu.”

The collisions of these micrometeorites triggered chemical reactions on magnetite, present on Ryugu’s surface, leading to the formation of iron nitride. The observation of iron nitride on magnetite surfaces provides insights into the intricate processes occurring in space environments.

As magnetite is exposed to the space environment, oxygen atoms are lost from its surface due to solar wind irradiation and micrometeorite impact heating. This leads to the formation of metallic iron on the surface, creating conditions conducive to the synthesis of iron nitride when reacting with ammonia.

In essence, this study sheds light on a celestial nitrogen transport system involving micrometeorites from icy bodies, offering a fresh perspective on the cosmic origins of essential building blocks for life on Earth.

Source: Kyoto University

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