Scientists find ancient clues to Earth’s origins in Bennu samples

In September 2023, the NASA-owned OSIRIS-REx probe delivered to Earth a capsule containing valuable material samples from the asteroid Bennu. Scientists were curious to see what they would find inside. They expected the collected material to become a treasure trove of knowledge about the Solar System's past. After initial problems opening the sample container, they managed to examine it. What they found was quite a surprise.

The results of preliminary analyses of the material collected from the asteroid Bennu were published in the scientific journal "Meteoritics & Planetary Science." As reported by NASA, the sample contained original ingredients that formed the Solar System. It turned out that the material is rich in carbon, nitrogen, and organic compounds, all of which are essential components of life as we know it. The sample was dominated by clay minerals, especially serpentinites, reflecting the type of rocks found on mid-ocean ridges on Earth.

The sample also detected magnesium and sodium phosphate, which was a significant surprise for the researchers. Earlier remote sensing data collected by the OSIRIS-REx spacecraft during Bennu's stay did not indicate their presence. According to NASA, the discovery of magnesium and sodium phosphate suggests that the asteroid might have broken off from an ancient, small, primitive oceanic world.

Earlier, a similar phosphate was discovered in a sample from the asteroid Ryugu, delivered by JAXA's (Japan Aerospace Exploration Agency) Hayabusa2 mission in 2020, but it differed from Bennu's. The latter stands out due to the greater purity of the material and the size of its grains, which is unprecedented in any other sample taken from a meteorite.

"The presence and state of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid," noted Dante Lauretta, co-author of the article and principal investigator of OSIRIS-REx. He added, "Bennu potentially could have once been part of a wetter world. Although, this hypothesis requires further investigation."

Despite its possible water-related past, Bennu remains a chemically primitive asteroid. Its elemental composition is close to that of the Sun. However, scientists emphasize that "the sample we returned is the largest reservoir of unaltered asteroid material on Earth right now." It has maintained its original state, neither melting nor solidifying since its formation, confirming its ancient origin. This means that the sample provides insight into the beginnings of our Solar System over 4.5 billion years ago.

"These findings underscore the importance of collecting and studying material from asteroids like Bennu — especially low-density material that would typically burn up upon entering Earth's atmosphere," said Dante Lauretta. He also explained, "this material holds the key to unraveling the intricate processes of solar system formation and the prebiotic chemistry that could have contributed to life emerging on Earth."

In the coming months, laboratories worldwide will receive parts of the Bennu samples for further research. "The Bennu samples are tantalizingly beautiful extraterrestrial rocks," said Harold Connolly, co-author of the study. "Each week, analysis by the OSIRIS-REx Sample Analysis Team provides new and sometimes surprising findings that are helping place important constraints on the origin and evolution of Earth-like planets".