Ryugu asteroid sample contains all five key components of DNA and RNA: the building blocks of all living things

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Scientists have discovered that samples of the Ryugu asteroid collected by Japan’s Hayabusa2 spacecraft contain the nucleobases adenine, guanine, cytosine, thymine and uracil, the building blocks of DNA and RNA on which all life is based.

Because asteroids like Ryugu were formed 4.6 billion years ago when planets were forming around the infant Sun, and have remained relatively unaffected since then, the discovery sheds new light on the chemical conditions that existed at the beginning of the Solar System.

Adenine, guanine, cytosine and thymine are the four bases of the genetic code that form specific pairs (adenine pairs with thymine, guanine with cytosine) to form the rungs of the double helix structure of DNA. In RNA, uracil replaces thymine to combine with adenine. The detection of these molecules in the asteroid indicates that they may have formed without the presence of life, and may hint at how these compounds may have been transported into the Solar System.

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The Japanese Aerospace Agency (JAXA) Hayabusa2 mission collected samples from the asteroid Ryugu between 2018 and 2019. The spacecraft returned these samples to Earth on December 5, 2020.

Carbonaceous asteroids like the spinning-top-sized Ryugu effectively contain a “fossil record” of unspoiled material from the early eras of the Solar System, which is why scientists are so eager to bring them back to Earth to study them up close and personal.

Study of two samples returned to Earth has previously revealed that liquid water once flowed on the surface of Ryugu, lending credence to the theory that these space rocks may have delivered water to our planet’s surface.

Asteroid Ryugu samples brought back to Earth

Asteroid Ryugu samples brought back to Earth (Image credit: JAXA/JAMSTEC)

The team, led by JAXA biogeochemist Toshiki Koga, analyzed two Ryugu samples returned by Hayabusa 2, finding adenine, guanine, cytosine, thymine and uracil. The results were compared with findings obtained when researchers studied samples returned from asteroid Bennu, and the Murchison and Orgueil meteorites collected from Australia in 1969 and France in 1864, respectively. The team found significant differences in the concentrations of nucleobases.

Ryugu contains approximately comparable amounts of the nucleobases, adenine and guanine (known as purines), to cytosine, thymine, and uracil (pyrimidine). However, the Murchison is more enriched in purine nucleobases, while the arguille samples from Bennu are more enriched in pyrimidine nucleobases.

Artist's concept of Japan's Hayabusa2 spacecraft near its target asteroid, currently called 1999 JU3.

Artist’s concept of Japan’s Hayabusa 2 spacecraft collecting samples from Ryugu (Image credit: JAXA)

These disparities may reflect the different evolutionary histories and environmental birthplaces of Ryugu, Bennu, and the parent bodies of the Murchison and Orgueil samples. The research further emphasizes the role of asteroids in creating the chemical diversity that allowed life to arise on Earth.

Perhaps the most important result of this study is the implication that the building blocks of DNA and RNA are widely distributed through the Solar System.

The team’s research was published in the journal Nature Astronomy.

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