Detailed analysis of samples returned from asteroid Ryugu has revealed the presence of all five of the typical “letters” of DNA and RNA, a finding that scientists say strengthens the argument that the building blocks of life may be widespread throughout the solar system.The findings were published in Nature Astronomyfrom materials collected Japan Aerospace Exploration Agency During the Hayabusa2 mission, it represented the most comprehensive chemical examination yet of one of the oldest objects in our universe.
What scientists discovered and why it’s important
At the heart of this discovery are nucleobases, the molecular components that encode the genetic information in DNA and RNA. These include adenine, guanine, cytosine, thymine, and uracil, often described as the “letters” that make up the instructions for life.For the first time, researchers confirmed the presence of these five viruses in samples from Ryugu.Toshiki KogaA biogeochemist at Japan’s Marine-Earth Science and Technology Agency and lead author of the study warned against over-interpreting the findings, he told AFP via AFP physical network: “This does not mean that life existed on Ryugu. Rather, their presence suggests that primitive asteroids could have produced and preserved molecules important for the chemistry associated with the origin of life.”
Researchers detected the building blocks of DNA, shown here, in samples collected from the asteroid Ryugu. (Image source: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, and Japan Industrial Technology Research Institute.)
In short, what scientists discovered was not life itself, but the complete chemical toolkit on which life as we know it depends.When combined with sugars such as ribose and phosphate groups, these molecules form DNA and RNA, the systems by which genetic information is stored and transmitted in every known organism on Earth.
How to collect and analyze samples
The material analyzed in the study comes from Hayabusa2 missionlaunched in 2014. The spacecraft arrived at Ryugu in 2018, landed on its surface in 2019, collected samples, and returned to Earth in 2020.The mission brought back a total of 5.4 grams of material, an amount smaller than a coin but invaluable to science because the material has remained essentially unchanged since the early solar system some 4.5 billion years ago.Early studies of a small portion of this material identified only one nucleobase, uracil, and 15 amino acids, which are the building blocks of proteins.
Photos of initial samples A0106 (total 38.4 mg) 6 and C0107 (total 37.5 mg) from asteroid Ryugu (162173) during the first landing sampling and second landing sampling respectively / Image source: JAXA / JAMSTEC
In this latest study, scientists obtained a larger sample, about 20 milligrams of asteroid dust, and used more refined analytical techniques to specifically look for nucleobases. The expanded range allowed them to detect the remaining four: adenine, guanine, cytosine and thymine.The researchers also studied the distribution of these molecules, comparing Ryugu’s chemical composition to that of other extraterrestrial samples, including the asteroid Bennu sampled by NASA’s OSIRIS-REx mission, and meteorites such as Murchison and Orgueil.
Chemical pattern that surprises researchers
Nucleobases are divided into two structural groups: purines (adenine and guanine), which have a double-ring structure, and pyrimidines (cytosine, thymine, and uracil), which have a single-ring structure.On Ryugu, the scientists found that the proportions between the two groups were balanced, unlike other samples. The Bennu and Orgueil meteorites show higher concentrations of pyrimidines, while the Murchison meteorite is rich in purines.
The “Ryuugu Story” illustration depicts all five typical nucleobases detected in samples brought back from the asteroid Ryugu by the Hayabusa2 mission. Image source: JAMSTEC
Most striking, however, is the consistent relationship between these ratios and the presence of ammonia, another molecule related to prebiotic chemistry.Koga explained the significance of this pattern in the study, stating:“Because no known formation mechanism predicts this relationship, this discovery may point to a previously unrecognized pathway for nucleobase formation in early solar system materials.”This suggests that the chemical environment in which these asteroids formed, particularly the availability of ammonia, may have determined how life-related molecules developed long before planets like Earth existed.
This explains the origin of life
The discovery raises a long-standing scientific question: Did life begin on Earth, or were its ingredients transported from space?Some theories suggest that life originated in environments such as deep-sea hydrothermal vents. Others propose that key organic molecules arrived via comets, asteroids or meteorites, seeding the early Earth with the chemicals needed for the emergence of life.César Menor Salván, an astrobiologist at the University of Alcalá who was not involved in the study, stressed that the findings do not prove that life originated in space. He told AFP in an interview that the results “do not suggest that life originated in space.”However, he added that when considered alongside Bennu’s findings, the data sheds a clearer light on the possibilities:“With this and the Bennu results, we have a pretty good idea of what organic materials could have formed under the conditions leading to the origin of life anywhere in the universe.”In other words, while life itself may not have originated on asteroids, the ingredients needed to build life appear to have formed naturally and widely.
Broader patterns across the solar system
This is not an isolated finding. In 2023, the same set of nucleobases was found in samples from Bennu, and similar molecules have been found in meteorites that have fallen to Earth.Ryugu and Bennu are both carbonaceous asteroids, which account for about 75% of the asteroids in the solar system and are rich in organic matter. Observations with the James Webb Space Telescope suggest they may even have a common origin, splitting off from a larger parent body billions of years ago.Because these objects are remnants of the earliest stages of planetary formation, they effectively act as time capsules, preserving the chemicals that existed before Earth fully formed.As the researchers wrote in their study: “The detection of multiple nucleobases in asteroid and meteorite material suggests their widespread occurrence throughout the solar system and strengthens the hypothesis that carbonaceous asteroids contributed to the probiotic chemical inventory of early Earth.”
what happens next
For scientists, the next step is not just confirming the existence of these molecules, but understanding how they form, evolve and survive in space.Coga said the team aims to further explore this issue:“We hope to further elucidate the mechanisms by which nucleobases essential for life are formed in space and how they become ubiquitous.”For now, the implication is clear: the chemicals that support life on Earth are not unique to this planet. It might be written into the fabric of the solar system itself, waiting to be assembled into something living under the right conditions.
