New discoveries from NASA’s OSIRIS-REx mission have revealed unexpected findings in asteroid samples retrieved from Bennu. The study, published in Nature, describes the presence of mineral remnants left behind by the evaporation of liquid water.
Traces of Ancient Water and Life’s Building Blocks Found on Bennu
Lead author Tim McCoy, speaking to Popular Science, stated that the team was not anticipating these components. “[Finding them] was completely unexpected,” he said. “The research team behind this study has hundreds of years of combined experience in meteorite analysis, yet some of these minerals have never been seen before.”
One significant aspect of this discovery is that the identified components must have formed from the evaporation of saline water solutions—liquids with high concentrations of dissolved salts. McCoy explained that the minerals contain water within their crystalline structures, suggesting the primary liquid involved was water. While trace amounts of carbon dioxide ice or other substances may have been present, the dominant element was water.
These findings suggest that liquid water was present at some point in Bennu’s history or, more precisely, in the history of the ancient parent asteroid from which Bennu originated. The parent asteroid was once a larger celestial body that broke into smaller fragments, including Bennu, sometime in the last 65 million years. According to McCoy, the parent body likely contained ice, which gradually melted over thousands of years due to heat generated by the decay of radioactive elements in the asteroid’s regolith.
This liquid water likely existed beneath the asteroid’s surface, forming pockets or veins rather than being exposed on the exterior. Because of this, the water may have remained in liquid form for an extended period, likely at near room temperature. The dissolved minerals in the solution could have also contributed to its persistence in liquid form, as saltwater typically has a lower freezing point than pure water—similar to how roads are salted during icy conditions to prevent freezing.
Once the water eventually evaporated, it left behind concentrated mineral deposits that surprised McCoy and his research team. When the parent asteroid fragmented, these minerals were preserved and passed on to Bennu. The first component identified in the Bennu samples was sodium carbonate, a mineral never before observed in any asteroid or meteorite sample. Since sodium carbonate’s crystalline structure includes water, its presence prompted researchers to search for additional water-soluble compounds. In total, the team discovered 11 such minerals, all of which were formed in salty water solutions before being left behind when the water evaporated.
The presence of liquid water in Bennu’s ancient parent body raises a fascinating possibility: that this celestial ancestor may have played a role in the early development of life’s basic components. The type of saline solutions found in Bennu’s predecessor could have provided an ideal environment for the formation of complex organic compounds. In an accompanying statement, McCoy said, “Now we know from Bennu that the raw ingredients for life combined in fascinating and complex ways on its parent body.” The study also suggests that similar salty water solutions might exist today within Saturn’s moon Enceladus and the dwarf planet Ceres.
McCoy emphasized that the presence of ice in Bennu’s parent asteroid suggests it must have formed beyond the solar system’s snow line—the distance from a star where temperatures are cold enough for water to freeze. NASA captured an image of this phenomenon occurring in a young star system in 2016. During the early formation of a solar system, a protoplanetary disk composed of gas and dust coalesces into planets and other celestial bodies. The location of the snow line plays a crucial role in determining which objects retain water in solid form, making it more likely for planets and asteroids beyond this line to be water-rich.
This concept supports one of the leading theories about the origins of Earth’s water, which proposes that our planet acquired its water through the capture of ice-rich celestial bodies formed beyond the snow line. If these bodies also contained saline solutions rich in organic compounds, it is theoretically possible that life’s early chemistry began in space before arriving on Earth.
Beyond theoretical possibilities, McCoy highlighted the importance of OSIRIS-REx’s ability to directly collect samples from Bennu. “These are incredibly rare minerals that could never have been identified from Earth,” he said. “Many of these minerals are unstable in Earth’s atmosphere. If they hadn’t been carefully preserved in a nitrogen-controlled environment after retrieval by a space mission, we would have never been able to study them in their original state.”
