This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Nitrogen is a key ingredient in the biomolecules that form the building blocks of life. Yet as an unbonded gas, it is far more likely to drift into space than to lock itself into solid compounds, making it difficult for astronomers to trace its journey to Earth in the distant past.
Through new research published in Nature Astronomy, a team led by Toru Matsumoto at Kyoto University has found some of the best evidence yet of how this journey happened, hidden inside grains of dust from the asteroid Ryugu. Nitrogen-bearing compounds, particularly ammonia, have already been spotted on the dwarf planet Ceres and on several carbon-rich asteroids, hinting that ammonia reservoirs might be common across the solar system. However, more direct evidence has proven difficult to come by.
When meteorites fall to Earth, very little nitrogen tends to be preserved, leaving astronomers perplexed as to why ammonia is so hard to find in the rocky leftovers when it appears so widespread across the solar system. Perhaps the best opportunity to answer this question came in 2020, when Japan's Hayabusa2 mission returned pristine samples from the near-Earth asteroid Ryugu. Untouched by the heat and weathering that damage material falling naturally through Earth's atmosphere, the sample gave a far more accurate picture of asteroid compositions than could ever be gleaned from meteorite remnants.
In their study, Matsumoto's team examined two tiny grains of the Ryugu sample using a combination of infrared spectroscopy, X-ray spectroscopy and electron microscopy. These techniques were sensitive enough to identify individual chemical bonds and map exactly where they sit within the rock. Just as they hoped, the researchers discovered several forms of nitrogen-bearing compounds: ammonium trapped inside clay minerals, molecules containing carbon-nitrogen bonds and crystals of sodium nitrate.
Crucially, all of it clustered around sodium carbonate—a mineral known to form as the last of the asteroid's salty water either froze or evaporated away. The arrangement suggested that these nitrogen compounds survived for millions of years while water moved through Ryugu's parent body, growing more concentrated as the water disappeared. Such concentration could have driven the kind of chemistry needed to build larger, more complex molecules, possibly echoing the formation of similar compounds on icy, salty bodies like Ceres.
Since they couldn't observe this reaction sequence directly, Matsumoto's team is cautious about its interpretation for now. But separate analysis of samples already returned from asteroid Bennu by NASA's OSIRIS-REx mission has independently turned up similar ammonium-bearing clays, lending weight to the wider pattern—even if it doesn't confirm the precise sequence of events they propose. Ultimately, if their predictions are correct, they would suggest that asteroids like Ryugu acted as slow-cooking chemical reactors, gradually concentrating nitrogen over vast stretches of time before delivering it to newly forming planets—perhaps supplying the very first building blocks for what would become life on Earth.
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