DNA’s Building Blocks Found on Asteroid Ryugu, Reinforcing Extraterrestrial Origin Theory

The detection of all five canonical nucleobases – adenine, guanine, cytosine, thymine and uracil – in samples from the asteroid Ryugu bolsters the hypothesis that the raw materials for life on Earth may have originated in space. This discovery, made by researchers analyzing samples returned by Japan’s Hayabusa2 mission, adds to a growing body of evidence suggesting that asteroids and meteorites delivered these crucial compounds to our planet.

Ryugu Samples Reveal Complete Nucleobase Set

Scientists have confirmed the presence of all five nucleobases in two Ryugu aggregate samples, A0480 and C0370 . These nucleobases are the fundamental building blocks of DNA and RNA, the molecules that carry genetic information in all known life forms. The findings, published in Nature Astronomy, represent a significant step forward in understanding the origins of life.

How Ryugu Differs from Other Extraterrestrial Samples

Interestingly, the composition of nucleobases in Ryugu differs from that found in other extraterrestrial materials. While Ryugu contains nearly equal amounts of purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil), samples from the Murchison meteorite are enriched in purines, and those from Bennu and Orgueil are richer in pyrimidines . This variation suggests that the nucleobases in these samples formed through different pathways, influenced by the unique physicochemical environments of their parent bodies.

The Role of Ammonia in Nucleobase Formation

Researchers observed a negative correlation between purine-to-pyrimidine ratios and ammonia levels in samples from Ryugu, Bennu, and Orgueil . This suggests that ammonia played a role in the formation of these nucleobases, potentially influencing the types of bases that were produced in each location.

Implications for the Origin of Life on Earth

The widespread presence of nucleobases throughout the Solar System, as demonstrated by the detection in asteroid and meteorite materials, strengthens the theory that carbonaceous asteroids contributed to the prebiotic chemical inventory of early Earth . The discovery supports the idea that these celestial bodies may have delivered the essential ingredients for life to our planet.

Hayabusa2 Mission and Sample Analysis

The Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 mission successfully collected samples from the C-type asteroid Ryugu in 2019 and returned them to Earth in December 2020 . High-performance liquid chromatography and high-resolution mass spectrometry were used to analyze the samples, revealing the presence of the five nucleobases . Previous analysis of Ryugu samples had already identified uracil and nicotinic acid (vitamin B3) .

How Were These Bases Formed?

Scientists hypothesize that high-energy radiation may have converted simple nitrogen-containing molecules, such as hydrogen cyanide, into nucleobases . This process could have occurred on asteroids, which then transported these vital compounds to Earth.