Nasa's asteroid Bennu sample reveals unexpected ancient secrets

In September 2023, NASA's OSIRIS-REx probe delivered a capsule to Earth containing valuable samples from the asteroid Bennu. Scientists were eager to see what the samples would reveal. They anticipated the collected material would offer a wealth of knowledge about the early Solar System. Despite initial difficulties in opening the sample container, researchers managed to examine its contents and were met with quite a surprise.

Preliminary analyses of the material collected from Bennu were published in the scientific journal "Meteoritics & Planetary Science." According to NASA, the sample contained primordial ingredients that formed the Solar System. The material was rich in carbon, nitrogen, and organic compounds, all of which are essential components of life. The sample was dominated by clay minerals, especially serpentinites, similar to rocks found on mid-ocean ridges on Earth.

The sample also revealed significant amounts of magnesium and sodium phosphate, an unexpected discovery for researchers. Earlier remote sensing data collected by OSIRIS-REx during its stay at Bennu did not indicate their presence. NASA stated that the discovery of these phosphates suggests that the asteroid might have broken off from an ancient, small, primitive oceanic world.

A similar phosphate had been discovered earlier in a sample from the asteroid Ryugu, delivered by JAXA's (Japan Aerospace Exploration Agency) Hayabusa2 mission in 2020. However, the phosphate from Bennu differs due to its greater purity 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 with an elemental composition close to that of the Sun. 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 offers crucial insights 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."