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Recent research conducted by Japanese collaborators has confirmed the presence of all five nucleobases—the essential components of DNA and RNA—in samples retrieved from asteroid Bennu by NASA’s OSIRIS-REx mission.
Asteroids are intriguing celestial bodies that may have played a crucial role in delivering both water and key chemical constituents for life to Earth billions of years ago. While meteorites made from asteroids have been found on Earth, their exposure to the atmosphere and biological processes complicates the analysis. Therefore, samples collected directly from space, in a pristine state, provide the most reliable data for study. Only two nations have successfully completed such sample return missions: Japan, with its Hayabusa and Hayabusa2 missions, and the United States with OSIRIS-REx.
In September 2023, NASA’s OSIRIS-REx mission successfully returned a total of 121.6 grams of sample from asteroid (101955) Bennu, marking the largest return of extraterrestrial material to Earth. Following this, a global team of scientists working on the OSIRIS-REx samples, led by Dr. Daniel Glavin and Dr. Jason Dworkin from NASA’s Goddard Space Flight Center, revealed the discovery of ammonia and nitrogen-rich soluble organic compounds within these specimens. Their findings were shared in the journal Nature Astronomy. Notably, researchers from Japan identified all five nitrogenous bases that are vital for DNA and RNA synthesis, bolstering the hypothesis that asteroids may have delivered life’s building blocks to our planet.
To safeguard the integrity of the Bennu samples, they were manipulated under nitrogen conditions to prevent any contamination from the terrestrial atmosphere. A specific subset of 17.75 mg was utilized for high-resolution mass spectrometry analysis at Kyushu University, targeting N-heterocycles—organic compounds featuring both carbon and nitrogen in a ring structure.
The research team comprised experts from various institutions: Associate Professor Yasuhiro Oba from Hokkaido University, Principal Researcher Yoshinori Takano from JAMSTEC and Keio University, Dr. Toshiki Koga from JAMSTEC, Professor Hiroshi Naraoka from Kyushu University, and Associate Professor Yoshihiro Furukawa from Tohoku University.
Their findings indicated a concentration of N-heterocycles in Bennu’s samples at approximately 5 nmol/g, which is significantly higher—about five to ten times—than that observed in samples from asteroid Ryugu. The analysis confirmed the presence of adenine, guanine, cytosine, thymine, and uracil, alongside other compounds like xanthine, hypoxanthine, and nicotinic acid (vitamin B3).
“In earlier studies, while uracil and nicotinic acid were noted in samples from Ryugu, the other four nucleobases were missing. This disparity in both the diversity and quantity of N-heterocycles between Bennu and Ryugu may suggest that different cosmic environments have influenced each asteroid,” commented Koga.
Additionally, the research team had also analyzed meteorite samples from Murchison and Orgueil under similar controlled conditions for comparative purposes. They discovered a markedly lower ratio of purines (adenine and guanine) to pyrimidines (cytosine, thymine, and uracil) in the Bennu samples when contrasted with those from Murchison and Orgueil.
“This discrepancy may be attributed to a variety of factors,” Oba explained. “Potential influences could include differences in the parent bodies of these celestial materials or variations in their formation paths. It’s also plausible that Bennu was subjected to a cold molecular cloud environment, which may favor the creation of pyrimidines.”
Naraoka emphasized the significance of these findings, stating, “Our research contributes to a broader understanding of nucleobase chemistry in the Bennu samples, which warrants further investigation.” Importantly, this study not only highlights the uniqueness of the Bennu specimens but also establishes a comparative framework for reanalyzing other meteorite collections worldwide.
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