Scientists have found all five nucleobases, the essential components of DNA and RNA, in samples brought back from asteroid Bennu by NASA’s OSIRIS-REx mission.
Researchers have identified all five nucleobases—crucial for DNA and RNA—within samples returned from asteroid Bennu through NASA’s OSIRIS-REx mission.
Asteroids, which are relatively small, airless entities in the inner Solar System, are believed to have played a significant role in delivering water and the essential chemical components for life to Earth billions of years ago. While meteorites found on Earth originate from asteroids, their exposure to moisture and biological activity on our planet complicates data interpretation. The most reliable evidence would come from untainted samples collected directly from asteroids in their original environment. So far, successful collection missions have been undertaken only by Japan (with Hayabusa and Hayabusa2) and the United States (with OSIRIS-REx).
In September 2023, NASA’s OSIRIS-REx mission brought back 121.6 grams of material from asteroid (101955) Bennu, marking the largest sample return ever achieved. An international group of scientists from the OSIRIS-REx sample analysis team, led by Dr. Daniel Glavin and Dr. Jason Dworkin at NASA’s Goddard Space Flight Center, reported the discovery of ammonia and nitrogen-rich organic compounds in these samples, with their research published in the journal Nature Astronomy. Notably, the Japanese team identified all five nitrogenous bases necessary for forming DNA and RNA, lending support to the idea that asteroids might have delivered life’s building blocks to our planet.
The Bennu samples were processed in a nitrogen atmosphere to avoid contamination from Earth’s environment. A 17.75 mg portion was analyzed for N-heterocycles—organic compounds that feature a ring structure composed of carbon and nitrogen—using advanced mass spectrometry techniques at Kyushu University.
The analysis was conducted by a research group that includes 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.
The results showed a concentration of N-heterocycles at about 5 nmol/g, which is 5-10 times greater than what was obtained from Ryugu samples. Alongside the five nitrogenous bases—adenine, guanine, cytosine, thymine, and uracil—researchers also detected xanthine, hypoxanthine, and nicotinic acid (vitamin B3).
“In prior studies of Ryugu, uracil and nicotinic acid were found, but the other four bases were missing. The variations in the amounts and types of N-heterocycles between Bennu and Ryugu may indicate the differing conditions to which these asteroids have been subjected in space,” explains Koga.
Additionally, samples from the meteorites Murchison and Orgueil were previously analyzed under the same conditions for comparison purposes. The research team found that the ratio of purines (adenine and guanine) to pyrimidines (cytosine, thymine, and uracil) was significantly lower in the Bennu samples compared to those from Murchison and Orgueil.
“There could be several reasons for this difference,” Oba notes. “It might relate to the origins of the parent bodies or the processes they underwent during their formation. Alternatively, Bennu may have been exposed to a colder molecular cloud situation where pyrimidines are more likely to form.”
“Our findings contribute to the broader understanding that all authors of the study are building upon, indicating a need for further investigation into the nucleobase chemistry of the Bennu samples,” Naraoka concluded. Another significant outcome from this research is that by comparing meteorites with Bennu samples, a reference point for reanalyzing other meteorites housed in global collections has been established.
