惑星科学：ベンヌのサンプルから有機物、アミノ酸、塩類が検出される

Rock and dust samples brought back from the near-Earth asteroid Bennu contain organic matter, including amino acids and all five DNA and RNA nucleobases, as well as salts that formed early in the history of Bennu’s parent body, according to two papers published in Nature Astronomy and Nature. The findings offer new insights into the early Solar System's chemistry.

In 2018, the OSIRIS-REx mission arrived at the near-Earth asteroid Bennu to collect pristine samples, untouched by alterations induced by Earth's atmosphere, to be analysed on Earth.

In the Nature Astronomy paper, Daniel Glavin and colleagues analysed the Bennu samples and found thousands of organic molecular compounds. These included 14 of the 20 protein amino acids present in life forms on Earth, 19 non-protein amino acids rare or absent in known biology, and all five biological nucleobases (adenine, guanine, cytosine, thymine, and uracil). Bennu was also found to be rich in nitrogen and ammonia-bearing compounds, which formed billions of years ago in cold, distant regions of our Solar System. The authors conclude that Bennu has a much richer complexity in organic matter than terrestrial biology and suggest that its parent body may have come from the outer Solar System, where ammonia and volatile ices are stable.

In the Nature paper, Timothy McCoy and colleagues analysed the Bennu samples and found a variety of salt minerals, including sodium-bearing phosphates and sodium-rich carbonates, sulfates, chlorides, and fluorides. These salts may have formed during the evaporation of brine that existed early in the history of Bennu’s parent body, indicating that water was once present. The potential presence of water, together with nucleobases, raises questions about the potential for prebiotic organic synthesis (the process that creates the building blocks for life), which will require further investigations, the authors conclude.