Unexpected Phosphate Found in Bennu Sample

The long-awaited analysis of the Bennu asteroid sample has unveiled fascinating insights into its composition. Predominantly composed of clay minerals, especially serpentine, the sample bears striking resemblance to rock types found at mid-ocean ridges on Earth, where mantle material encounters water. This interaction not only forms clay but also produces minerals like carbonates, iron oxides, and iron sulfides.

Despite its possible history with water, Bennu remains a chemically primitive asteroid, with elemental proportions closely resembling those of the Sun. This composition offers a glimpse into the early days of our solar system, over 4.5 billion years ago. These rocks have retained their original state, having neither melted nor resolidified since their formation, affirming their ancient origins.

One of the most exciting discoveries is the presence of carbon and nitrogen in abundance. These elements are crucial in understanding the environments where Bennu’s materials originated and the chemical processes that transformed simple elements into complex molecules, potentially laying the groundwork for life on Earth.

The OSIRIS-REx Sample Analysis Team confirmed the asteroid is rich in organic compounds, all vital for life. As Dante Lauretta, co-lead author of the paper and principal investigator for OSIRIS-REx at the University of Arizona, Tucson, stated, “The sample we returned is the largest reservoir of unaltered asteroid material on Earth right now.”

However, the most intriguing discovery in the Bennu sample is the presence of magnesium-sodium phosphate, a compound crucial for biochemistry and life processes on Earth. The identification of this water-soluble phosphate mineral was unexpected, as it was not detected in the spacecraft’s remote sensing data from Bennu.

The presence of phosphates in the Bennu sample raises questions about the geochemical processes that concentrated these elements, offering valuable clues about the asteroid’s historical conditions. According to Dante Lauretta, “The presence and state of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid. Bennu potentially could have once been part of a wetter world. Although, this hypothesis requires further investigation.”

While a similar phosphate was identified in the asteroid Ryugu sample delivered by JAXA’s Hayabusa2 mission in 2020, the magnesium-sodium phosphate in the Bennu sample is notable for its purity and the unprecedented size of its grains in any meteorite sample.

The discovery of these phosphate minerals has significant implications for our understanding of the early solar system and the potential for life beyond Earth. Phosphates are essential for the formation of DNA, RNA, and other biomolecules that are the building blocks of life as we know it. Their presence in the Bennu sample suggests that the asteroid, or the parent body from which it originated, could have harbored conditions favorable for the development of prebiotic chemistry.

Furthermore, the presence of phosphates in asteroids like Bennu may have played an important role in the delivery of these essential compounds to early Earth, contributing to the emergence of life on our planet. As Jason Dworkin, a co-author on the paper and the OSIRIS-REx project scientist at NASA’s Goddard Space Flight Center, stated, “OSIRIS-REx gave us exactly what we hoped: a large pristine asteroid sample rich in nitrogen and carbon from a formerly wet world.”