Component of RNA Found in Asteroid Ryugu Samples
Samples from the asteroid Ryugu collected by the Hayabusa2 mission contain nitrogenous organic compounds, including the nucleobase uracil, which is a part of RNA.
Researchers have analyzed samples of asteroid Ryugu collected by the Japanese Space Agency’s Hayabusa2 spacecraft and found uracil—one of the informational units that make up RNA, the molecules that contain the instructions for how to build and operate living organisms. Nicotinic acid, also known as Vitamin B3 or niacin, which is an important cofactor for metabolism in living organisms, was also detected in the same samples.
This discovery by an international team, led by Associate Professor Yasuhiro Oba at Hokkaido University, adds to the evidence that important building blocks for life are created in space and could have been delivered to Earth by meteorites. The findings will be published today (March 21) in the journal Nature Communications.
“Scientists have previously found nucleobases and vitamins in certain carbon-rich meteorites, but there was always the question of contamination by exposure to the Earth’s environment,” Oba explained. “Since the Hayabusa2 spacecraft collected two samples directly from asteroid Ryugu and delivered them to Earth in sealed capsules, contamination can be ruled out.”
The researchers extracted these molecules by soaking the Ryugu particles in hot water, followed by analyses using liquid chromatography coupled with high-resolution mass spectrometry. This revealed the presence of uracil and nicotinic acid, as well as other nitrogen-containing organic compounds.
“We found uracil in the samples in small amounts, in the range of 6–32 parts per billion (ppb), while vitamin B3 was more abundant, in the range of 49–99 ppb,” Oba elaborated. “Other biological molecules were found in the sample as well, including a selection of amino acids, amines, and carboxylic acids, which are found in proteins and metabolism, respectively.” The compounds detected are similar but not identical to those previously discovered in carbon-rich meteorites.
The team hypothesizes that the difference in concentrations in the two samples, collected from different locations on Ryugu, is likely due to the exposure to the extreme environments of space. They also hypothesized that the nitrogen-containing compounds were, at least in part, formed from the simpler molecules such as ammonia, formaldehyde, and hydrogen cyanide. While these were not detected in the Ryugu samples, they are known to be present in cometary ice—and Ryugu could have originated as a comet or another parent body that had been present in low-temperature environments.
“The discovery of uracil in the samples from Ryugu lends strength to current theories regarding the source of nucleobases in the early Earth,” Oba concludes. “The OSIRIS-REx mission by NASA will be returning samples from asteroid Bennu this year, and a comparative study of the composition of these asteroids will provide further data to build on these theories.”
Reference: “Uracil in the carbonaceous asteroid (162173) Ryugu” 21 March 2023, Nature Communications.
Funding: Japan Aerospace Exploration Agency, Deutsches Zentrum für Luft- und Raumfahrt, Centre national d’études spatiales, National Aeronautics and Space Administration, Australian Space Agency, Japan Society for the Promotion of Science
The Hayabusa2 mission was a Japanese space mission launched in 2014 with the aim of studying the asteroid Ryugu and bringing back samples to Earth. The spacecraft arrived at Ryugu in 2018 and spent over a year studying the asteroid’s surface and interior, deploying multiple landers and rovers to conduct experiments and collect data. In 2019, the spacecraft used a projectile to create a small crater on the asteroid’s surface, collecting subsurface material from the impact site. The spacecraft returned to Earth in December 2020, bringing back the first-ever subsurface samples from an asteroid. The mission provided valuable insights into the formation of the solar system and the composition of asteroids.