A recent examination of materials procured from the asteroid known as Ryugu has successfully identified all five fundamental nucleobases essential for the formation of RNA and DNA.
This marks not the inaugural instance of isolating the complete set of these five compounds from asteroidal matter—the asteroid Bennu previously achieved this distinction. However, this contemporary finding amplifies the significance of the discovery: we now possess evidence of a full ensemble of nucleobases on two distinct carbonaceous asteroids.
This revelation strongly implies that the foundational components for life might be far from scarce throughout our Solar System.
“The identification of a diverse array of nucleobases within asteroid and meteorite specimens underscores their pervasive presence across the Solar System,” state a research collective spearheaded by biogeochemist Toshiki Koga of the Japan Agency for Marine-Earth Science and Technology. “Furthermore, it corroborates the conjecture that carbon-rich asteroids were instrumental in furnishing the prebiotic chemical landscape of primordial Earth.”
All terrestrial life depends on two primary molecular entities for the retention and transmission of genetic code: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). These, in turn, are constituted from five cardinal molecular constituents: adenine, cytosine, guanine, thymine, and uracil.
Comprehending the prevalence of these constituents on early Earth, along with their potential origins, is paramount to elucidating the genesis of life itself.
Asteroids such as Ryugu and Bennu likely played a pivotal role in the dissemination of these molecular precursors. Carbonaceous asteroids are recognized for harboring a broad spectrum of organic compounds that originated during the nascent stages of the Solar System’s evolution.
In recent years, two ambitious extraterrestrial missions have successfully returned samples, meticulously collected from the surfaces of asteroids, directly to the eager hands of scientific researchers: JAXA’s Hayabusa2 mission to Ryugu and NASA’s OSIRIS-REx mission to Bennu.
The announcement concerning the discovery of all five nucleobases on Bennu was made in January of 2025. At that juncture, however, Ryugu had yielded only one of these compounds: uracil.
The recent research initiative has now successfully completed the identification of the full complement. Koga and his associates meticulously analyzed two distinct samples derived from Ryugu’s material, identifying all five canonical nucleobases within both specimens.
Asteroids are not the sole celestial bodies from which scientists have detected nucleobases. Specifically, two carbonaceous meteorites—extraterrestrial rocks that have descended to Earth—also satisfy this criterion: Murchison and Orgueil.
To obtain a more comprehensive understanding of nucleobase content and their distribution across the Solar System, the researchers performed a comparative analysis between the constituents of Ryugu and those found in Bennu, Murchison, and Orgueil, uncovering noteworthy disparities.
The five fundamental nucleobases are classified into two distinct categories: the purines, which include adenine and guanine; and the pyrimidines, comprising cytosine, thymine, and uracil.
Ryugu exhibited a roughly equitable distribution of purines and pyrimidines. In contrast, Bennu and Orgueil demonstrated a higher proportion of pyrimidines, while Murchison was found to be richer in purines.
The researchers determined that these variations are intrinsically linked to the ammonia concentrations present in the samples, suggesting that the chemical milieu within asteroid parent bodies can exert an influence on the types of nucleobases that are synthesized.
Furthermore, the detection of thymine presents a particularly fascinating aspect of this discovery. The constituent molecules of DNA and RNA exhibit subtle distinctions. DNA is composed of adenine, cytosine, guanine, and thymine—forming the basis of the widely recognized ACGT sequence. RNA, conversely, is comprised of adenine, cytosine, guanine, and uracil.
One prominent hypothesis regarding the abiogenesis of life is the “RNA World” theory, which posits that RNA preceded DNA. Thymine is recognized as a chemically modified variant of uracil, and uracil is generally considered more readily produced through prebiotic chemical processes. This has led scientists to infer that uracil was more abundantly available for the early Earth’s chemical environment, which ultimately fostered the emergence of life.
The earlier finding of solely uracil on Ryugu aligned seamlessly with this theoretical framework. The current discovery of thymine indicates that asteroidal chemistry possesses the capacity to generate both nucleobases, rather than exhibiting a strong preference for one over the other.
These research findings suggest that the synthesis of nucleobases may be a widespread phenomenon on carbon-rich celestial bodies within our Solar System, which could have subsequently delivered the complete array of life’s essential ingredients to Earth through bombardment during its formative stages.
“The ubiquitous identification of all five canonical nucleobases in samples derived from the carbonaceous asteroids Ryugu and Bennu underscores the potential contribution of these exogenic molecules to the organic substrate that facilitated prebiotic molecular evolution and, ultimately, enabled the emergence of RNA and DNA on the early Earth,” the researchers articulate.
The outcomes of this investigation have been formally disseminated in the esteemed journal Nature Astronomy.
