A detailed analysis of samples returned from the asteroid Ryugu has revealed the presence of all five canonical “letters” of DNA and RNA, a finding scientists say strengthens the case that the basic ingredients for life may be widespread across the solar system.The discovery, published in the journal Nature Astronomy, comes from material collected by Japan’s Japan Aerospace Exploration Agency during its Hayabusa2 mission, and represents the most comprehensive chemical examination yet of one of the oldest objects in our cosmic neighbourhood.
What scientists found, and why it matters
At the centre of the discovery are nucleobases, the molecular components that encode genetic information in DNA and RNA. These include adenine, guanine, cytosine, thymine and uracil, often described as the “letters” that form the instructions for life.For the first time in samples from Ryugu, researchers confirmed the presence of all five.Toshiki Koga, a biogeochemist at the Japan Agency for Marine-Earth Science and Technology and the study’s lead author, cautioned against overinterpreting the finding, telling AFP via Phys.org: “This does not mean that life existed on Ryugu. Instead, their presence indicates that primitive asteroids could produce and preserve molecules that are important for the chemistry related to the origin of life.”
Researchers detected the building blocks of DNA in samples collected from asteroid Ryugu, pictured here. (Image credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu and AIST.)
In simpler terms, what scientists have found is not life itself, but a complete chemical toolkit that life as we know it depends on.These molecules, when combined with sugars like ribose and phosphate groups, form DNA and RNA, the systems that store and transmit genetic information in every known organism on Earth.
How the samples were collected and analysed
The material analysed in the study comes from the Hayabusa2 mission, launched in 2014. The spacecraft reached Ryugu in 2018, touched down on its surface in 2019, and collected samples before returning them to Earth in 2020.In total, the mission brought back 5.4 grams of material, an amount smaller than a coin, but scientifically invaluable because it has remained largely unchanged since the early solar system, around 4.5 billion years ago.Earlier studies of a smaller portion of this material had identified only one nucleobase, uracil, along with 15 amino acids, which are the building blocks of proteins.
Photographs of initial samples A0106 (total 38.4 mg)6 and C0107 (total 37.5 mg) from the asteroid Ryugu (162173) during the 1st touchdown sampling and 2nd touchdown sampling, respectively/ Credit: JAXA / JAMSTEC
For this latest research, scientists were given a larger sample, about 20 milligrams of asteroid dust, and used more refined analytical techniques to search specifically for nucleobases. That expanded scope allowed them to detect the remaining four: adenine, guanine, cytosine and thymine.The researchers also examined how these molecules were distributed, comparing Ryugu’s chemical profile with that of other extraterrestrial samples, including the asteroid Bennu, sampled by NASA’s OSIRIS-REx mission, and meteorites such as Murchison and Orgueil.
A chemical pattern that surprised researchers
Nucleobases fall 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, scientists found a balanced ratio between these two groups, unlike other samples. Bennu and the Orgueil meteorite showed higher concentrations of pyrimidines, while the Murchison meteorite was richer in purines.
The “Ryugu Story” illustration depicting the detection of all five canonical nucleobases in samples returned from asteroid Ryugu by the Hayabusa2 mission. Credit: JAMSTEC
What stood out most, however, was a consistent relationship between these ratios and the presence of ammonia, another molecule relevant to prebiotic chemistry.Koga explained the significance of this pattern in the study, noting:“Because no known formation mechanism predicts such a relationship, this finding 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 shaped how life-related molecules developed long before planets like Earth existed.
What this says about the origin of life
The discovery feeds into a long-standing scientific question: Did life begin on Earth, or were its ingredients delivered from space?Some theories argue that life originated in environments such as deep-sea hydrothermal vents. Others propose that key organic molecules arrived via comets, asteroids or meteorites, seeding early Earth with the chemistry needed for life to emerge.César Menor Salván, an astrobiologist at the University of Alcalá who was not involved in the study, emphasised that the findings do not prove life began in space. Speaking to AFP, he said the results “do not suggest that the origin of life took place in space.”However, he added that when considered alongside findings from Bennu, the data offers a clearer picture of what is possible:“With this and the results from Bennu, we have a very clear idea of which organic materials can form under prebiotic conditions anywhere in the universe.”In other words, while life itself may not have originated on asteroids, the ingredients required to build it appear to form naturally and widely.
A broader pattern across the solar system
This is not an isolated discovery. The same set of nucleobases was identified in samples from Bennu in 2023, and similar molecules have been found in meteorites that have fallen to Earth.Ryugu and Bennu are both carbonaceous asteroids, a class that makes up roughly 75% of asteroids in the solar system and is known to be rich in organic material. Observations from the James Webb Space Telescope suggest they may even share a common origin, having broken off from a larger parent body billions of years ago.Because these objects are remnants from the earliest stages of planetary formation, they effectively act as time capsules, preserving the chemistry that existed before Earth fully formed.As the researchers wrote in their study: “The detection of diverse nucleobases in asteroid and meteorite materials demonstrates their widespread presence throughout the Solar System and reinforces the hypothesis that carbonaceous asteroids contributed to the prebiotic chemical inventory of early Earth.”
What comes next
For scientists, the next step is not simply confirming the presence of these molecules, but understanding how they form, evolve and survive in space.Koga said the team aims to push further into that question:“We want to further elucidate the mechanisms by which nucleobases essential for life are formed in space and how they come to exist universally.”For now, the implication is clear: the chemistry that underpins life on Earth is not unique to this planet. It may be written into the fabric of the solar system itself, waiting, under the right conditions, to be assembled into something living.
