Researchers have found salts in samples from asteroid Ryugu. Combined with similar salty discoveries from asteroid Bennu, the finding suggests that aqueous incubators of life’s first ingredients may have been relatively common in the early solar system.
Astrochemists have found sugars and nucleotide bases outside of Earth before, but an extraterrestrial environment in which these ingredients could combine—and possibly create life—remained elusive. The salts lifted from the two asteroids are evidence that just such an incubator (salty liquid water) existed in the early solar system.
The results from Ryugu were reported in Nature Astronomy in November 2024, and those from Bennu were reported in January 2025. The parallel discoveries paint a compelling picture of the early solar system.
“We can now say, for the first time, that 4.5 billion years ago—long before most of us thought it could happen—we had both the ingredients and the environment in which the early stages of organic evolution towards life could begin,” said Tim McCoy, a curator of meteorites at the Smithsonian’s National Museum of Natural History who studied the Bennu samples. Such evolution “didn’t happen on a large, icy moon or a large, warm planet like Earth. It was actually happening in asteroids at the birth of the solar system. From day one of the solar system, we were seeing this organic evolution.”
Avoiding the Elements
Meteorites, typically fragments of larger space rocks, are exposed to moisture as they fall to Earth. When this happens, any water-soluble materials they may have had react and disappear. The atmosphere, McCoy said, is “actually removing some of what was there to start with.” That means meteorites themselves are not always reliable for studying whether their parent bodies contained water.
Two recent space missions sought to bring back regolith directly from asteroids. JAXA’s (Japan Aerospace Exploration Agency) Hayabusa2 visited Ryugu in 2019, returning samples in 2020. NASA’s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) collected samples of Bennu in 2020 and returned to Earth in 2023.
“Meteorites have been studied for about 150 years. But nobody had found such kind of salts, so we are surprised.”
Most researchers think common, carbon-rich asteroids like Ryugu and Bennu, known as C-type asteroids, contain water and organic material left over from the formation of the solar system.
Toru Matsumoto, an astromaterials scientist from Kyoto University, and his colleagues found thin white veins in tiny samples from Ryugu. Using electron microscopy and radiation X-ray analysis, they identified the minerals and their chemical compositions.
The Ryugu sample showed a composition remarkably similar to that of samples from Bennu. Both asteroids contain clays, iron oxides, iron sulfides, and carbonates, suggesting they were altered by water.
The Ryugu samples also contained sodium carbonate salts. “Meteorites have been studied for about 150 years,” Matsumoto said. “But nobody had found such kind of salts, so we are surprised.”
Aqueous Evidence
Salty water provides a unique environment for the development of life. A sodium-rich solution with minimal calcium allows phosphate to stay in the solution, which is important because phosphate combined with sugar forms the backbone of RNA and DNA. Sodium-rich solutions can also catalyze chemical reactions between organics and precipitate minerals that act as templates for those reactions.
Evaporite salts such as sodium carbonate are the last minerals to precipitate out of salty water. Their presence on Ryugu suggests that “there were really large volumes of water on this asteroid, which is kind of weird, because it’s a small rock floating in space, so it’s not going to have [an] actual ocean on it,” said Prajkta Mane, a planetary scientist at the Lunar and Planetary Institute in Texas who was not involved with the research.
“These two sample sets really provide our first glimpse of a portion of the solar system that was previously poorly sampled.”
“In order to get something like these evaporites, you have to have a pocket of water that’s evaporating,” McCoy said. “I don’t think we had any proof of that before, and now we do.”
That samples from both Bennu and Ryugu contain salts suggests that watery environments were common in the outer solar system, where the asteroids’ parent bodies likely formed. “Processes that occurred on one likely occurred on many or most similar asteroids, and likely [on] icy moons,” McCoy said. The salts resemble those recently discovered on the dwarf planet Ceres and on icy moons orbiting Jupiter and Saturn, which likely host subsurface oceans.
“These two sample sets really provide our first glimpse of a portion of the solar system that was previously poorly sampled,” McCoy said.
—Molly Herring (@mollyherring.bsky.social), Science Writer
Citation: Herring, M. (2025), Asteroid samples suggest a solar system of ancient, salty incubators,
Eos, 106, https://doi.org/10.1029/2025EO250122. Published on 2 April 2025.
Text © 2025. The authors.
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