A detailed analysis of the samples returned from the asteroid Ryugu has revealed the presence of five “canonical” letters of DNA and RNA, which scientists have found to strengthen the fact that the basic ingredients of life may be widespread around the sun.This 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 extensive chemical analysis yet of one of the oldest objects in our universe.
What scientists have found, and why it matters
At the heart of the discovery are nucleobases, molecular units that encode genetic information in DNA and RNA. These include adenine, guanine, cytosine, thymine and uracil, which are often described as the “letters” that make up the instructions of life.For the first time in Ryugu’s samples, researchers have confirmed the presence of five.Toshiki Koga, a biochemist at the Japan Institute of Earth Science and Technology and lead author of the study, warned AFP via Phys.org that: “This does not mean that life existed on Ryugu.
Researchers found blocks of DNA in samples collected from the asteroid Ryugu, shown here. (Image credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University and AIST.)
Simply put, what scientists have discovered is not life itself, but a complete set of chemical tools upon which life as we know it depends.These molecules, when combined with sugars such as 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 analyzed
The material analyzed in this study comes from the Hayabusa2 mission, which began in 2014. The spacecraft arrived at Ryugu in 2018, touched down on its surface in 2019, and collected samples before returning them to Earth in 2020.In total, the mission returned 5.4 grams of material, which is smaller than a coin, but scientifically important because it has remained unchanged since the early days of the planets, 4.5 billion years ago.Earlier studies of a small part of this material found only one nucleobase, uracil, as well as 15 amino acids, which are the building blocks of proteins.
Photographs of the first samples A0106 (total 38.4 mg)6 and C0107 (total 37.5 mg) from asteroid Ryugu (162173) during the 1st touchdown sampling and the 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 refined analytical methods to specifically look for nucleobases. That expanded space allowed them to recognize four residues: adenine, guanine, cytosine and thymine.The researchers also analyzed how these molecules are distributed, comparing the chemical composition of Ryugu with that of other extraterrestrial samples, including the asteroid Bennu, taken by NASA’s OSIRIS-REx mission, and meteorites such as Murchison and Orgueil.
A chemical process that surprised researchers
Nucleobases fall into two structural groups: purines (adenine and guanine), which have a two-ring structure, and pyrimidines (cytosine, thymine and uracil), which have a single ring structure.In Ryugu, scientists have found a balanced ratio between these two groups, unlike other examples. The Bennu and Orgueil meteorites showed more pyrimidines, while the Murchison meteorite was rich in purines.
The Ryugu Story image showing the discovery of the five canonical nucleobases in samples returned from the asteroid Ryugu by the Hayabusa2 mission. Credit: JAMSTEC
However, what stood out the most was the consistent relationship between these ratios and the presence of ammonia, another molecule related to prebiotic chemistry.Koga explained the importance of this pattern in education, saying:“Because there is no known structural method that predicts such a relationship, this result may point to a previously unknown way of forming nucleobases in the early solar system.”This suggests that the chemical environment these asteroids formed in, particularly the availability of ammonia, may have shaped how life-related molecules evolved long before Earth-like planets existed.
What this says about the origin of life
The discovery raises a long-standing scientific question: Did life begin on Earth, or were its components introduced into space?Other theories argue that life originated in places like deep ocean hydrothermal vents. Others suggest that essential organic molecules arrived via comets, asteroids or meteorites, seeding the early Earth with the chemistry necessary for life to emerge.César Menor Salván, an astronomer at the University of Alcalá who was not involved in the research, emphasized that the findings do not prove that 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 together with the findings from Bennu, the data paint a clear picture of what is possible:“With this and the Bennu result, we have a clear idea of how organic materials can form under prebiotic conditions anywhere in the universe.”In other words, even though life itself may not have originated on asteroids, the ingredients needed to build it appear to be naturally occurring and widespread.
A comprehensive approach throughout the solar system
This is not a unique discovery. The same group of nucleobases was identified in Bennu samples in 2023, and similar molecules have been found in meteorites that have fallen to Earth.Both Ryugu and Bennu are carbonaceous asteroids, a group that makes up about 75% of the asteroids in the solar system and are known to harbor abundant life. Observations from the James Webb Space Telescope suggest that they may have a common origin, as they broke up from a large parent body billions of years ago.Because these materials are remnants from the early stages of planetary formation, they effectively act as time capsules, preserving the chemistry that existed before Earth was fully formed.As the researchers wrote in their study: “The discovery of various nucleobases in asteroids and meteorites indicates their widespread presence throughout the Solar System and confirms the idea that carbonaceous asteroids contributed to the production of early Earth chemicals.”
What follows
For scientists, the next step is not only to confirm the existence of these molecules, but to understand how they form, change and survive in space.Koga said the team is ready to move forward on that question:“We want to shed more light on the mechanisms by which nucleobases essential for life are formed in the atmosphere and how they came to be in the universe.”For now, the implication is clear: the chemistry that supports life on Earth is unlike this planet. It may be written into the fabric of the planetary system itself, waiting, under the right conditions, to be assembled into a living organism.
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