Ryugu Asteroid Samples Contain All DNA and RNA Building Blocks

Samples returned from the near-Earth asteroid Ryugu by JAXA's Hayabusa2 mission have been found to contain all five nucleobases that make up DNA and RNA — adenine, guanine, cytosine, thymine, and uracil. The discovery, published in Nature, provides the strongest evidence yet that the molecular ingredients for life were delivered to early Earth by meteorites and asteroids.

Why This Matters

The detection of all five nucleobases in a single, pristine carbonaceous asteroid sample eliminates a key objection to the panspermia hypothesis — the idea that life's building blocks arrived from space. Previous studies of meteorite falls on Earth had found some nucleobases, but contamination from terrestrial sources was always a concern. Ryugu's samples, collected in the vacuum of space and sealed upon return, provide an unambiguous answer.

The Ryugu Samples

Hayabusa2 visited the near-Earth asteroid Ryugu in 2018-2019, collecting approximately 5.4 grams of surface and subsurface material. The subsurface samples were particularly valuable because they had been shielded from solar radiation for billions of years, preserving organic molecules in a near-pristine state.

Key Findings

• All five nucleobases detected simultaneously in a single extraterrestrial sample for the first time
• Nucleobase concentrations consistent with formation through photochemical reactions in interstellar ice analogs
• Detection of additional organic compounds including amino acids (previously reported) and a variety of other prebiotic molecules
• The isotopic signatures rule out terrestrial contamination

Implications

The finding supports the model that:

1. Organic molecules formed in the interstellar medium or on early solar system bodies
2. These molecules were incorporated into asteroids and comets
3. During the Late Heavy Bombardment (~4.1-3.8 billion years ago), these bodies delivered organic material to Earth
4. Once on Earth, these molecules participated in the chemical reactions that led to the origin of life

This does not prove that life originated in space, but it demonstrates that the raw materials were abundantly available on early Earth from extraterrestrial sources, significantly reducing the number of steps needed for life to emerge.

Source: Nature | Phys.org | HN Discussion