Asteroid Ryugu samples contain all five DNA and RNA nucleobases

According to a recent study, all five key nucleobases, the molecular “letters” of life, have been found in samples collected from the asteroid Ryugu.

Particles obtained from asteroids offer a glimpse of the chemical ingredients that may have contributed to the emergence of life on Earth. The Ryugu samples were brought back to Earth from space in 2020 by the Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA).

In 2023, an international research team reported finding uracil, one of the nucleobases, in these samples. Then, in a study recently published in the journal Nature Astronomy, a team of Japanese scientists confirmed that all five nucleobases are present in this primitive asteroid material.

This suggests that these building blocks of life may have been widespread throughout the solar system in its early days.

Why look for nucleobases

Nucleobases are nitrogen-containing organic molecules that serve as the “letters” of genetic information in DNA and RNA. The five main nucleobases are adenine and guanine (purines) and cytosine, thymine and uracil (pyrimidines).

These molecules combine with sugars and phosphates to form nucleotides, the basic units of genetic material. Without nucleobases, the genetic code that allows living things to grow, reproduce and evolve could not exist.

By studying the purines and pyrimidines in the Ryugu samples, scientists can reconstruct the chemical history of primitive asteroids. This gives a better understanding of how the building blocks of life formed and how they may have been present across the solar system.

Hayabusa2 brought a total of 5.4 grams of primitive asteroid material back to Earth. The researchers had to work in an extremely clean laboratory environment to keep the samples from being contaminated. They extracted organic molecules using water and hydrochloric acid, then purified them for analysis.

The researchers found all five nucleobases in both of the Ryugu samples they analyzed, in broadly similar amounts.

Key building blocks of genetic material found in space

The results are consistent with earlier findings from space rocks. Nucleobases and a variety of other organic molecules had previously been found in the Murchison meteorite, which fell in Australia in 1969, and the Orgueil meteorite, which fell in France in 1864.

Of course, meteorites that fall to Earth can be contaminated as they travel through space or land on the surface. But in 2025, all five nucleobases were also identified in pristine samples obtained by NASA’s mission to the asteroid Bennu.

Asteroids such as Ryugu and Bennu, as well as the parent body of the Orgueil meteorite, are remnants of the early solar system. They can preserve material in a nearly unchanged state for about 4.5 billion years.

Interestingly, there are chemical differences among these asteroids. The Murchison meteorite is rich in purines, while Bennu and the Orgueil meteorite contain more pyrimidines. This balance may have been influenced by ammonia, a key molecule that determines which nucleobases form.

By comparing the relatively pristine samples from Ryugu with meteorites such as Murchison and Orgueil, researchers are tracing the journey of life’s molecular building blocks through space.

The results suggest that key components of genetic material may have formed in space and then been delivered to the early Earth. In other words, the history of life on Earth may be closely tied to the chemistry of these ancient asteroids.

The pathway of life’s building blocks

These findings show that carbon-rich asteroids throughout the solar system hold a variety of prebiotic chemical ingredients. However, the specific molecular makeup, including the balance of purines and pyrimidines, varies with each asteroid’s chemical environment and history.

Because the Ryugu samples were collected directly in space and protected from contamination on Earth, they are among the clearest records of the chemistry of the ancient solar system.

The discovery of all five nucleobases on Ryugu suggests that the molecular ingredients of life may already have been forming in space billions of years ago. Asteroids may have delivered these ingredients to the early Earth, which would mean that the origin of life is part of a larger cosmic chemical story.

This article was translated from the Korean edition of Science Monitor with AI assistance and reviewed by our editors.