Scientists Discover All Five DNA and RNA Bases in Asteroid Samples

An international team of researchers has discovered the five nucleobases that form the foundation of DNA and RNA within material retrieved from the asteroid Ryugu. The finding offers significant new insight into whether the fundamental building blocks of biology originated in space before being delivered to our planet.

The identified bases include adenine, guanine, cytosine, thymine, and uracil, which work together to store and transmit genetic information in living organisms. Detecting these compounds in an extraterrestrial object is particularly crucial because the samples from Ryugu were collected directly in space by the Japanese Hayabusa2 mission and sealed in a capsule, preventing any contamination by terrestrial air, rain, or bacteria.

For centuries, scientists relied on meteorites that fell haphazardly to Earth, often absorbing moisture and environmental elements over months or years. This left a lingering question regarding whether interesting molecules found inside came from space or were acquired locally. Pristine samples from space missions, such as the 5.4 grams brought from Ryugu in 2020 and the roughly 120 grams gathered from asteroid Bennu by NASA's OSIRIS-REx mission in 2023, have finally resolved that doubt.

Advanced analytical techniques have allowed scientists to examine these samples without destroying fragile molecules. In recent analyses, researchers utilized sensitive equipment and cold water instead of traditional, highly aggressive hot formic acid treatments. This careful approach recently enabled a team from the Japanese institute JAMSTEC, led by Toshiki Koga, to identify all five canonical bases in two small grains of Ryugu, mirroring similar discoveries made in Bennu samples by a NASA group led by Daniel Glavin.

Beyond genetic building blocks, researchers have found a wealth of other organic material in the space rocks. Analyses led by Hiroshi Naraoka of Kyushu University identified 15 different types of amino acids in Ryugu, while Glavin's team found 14 of the 20 amino acids used by terrestrial life to build proteins in Bennu. Additionally, studies have detected various sugars, such as ribose—the sugar component of ARN—along with salty minerals indicating that ancient brine and evaporating salt ponds once existed on the parent bodies of these asteroids.

Despite these rich inventories, researchers emphasize that finding these molecules does not mean life itself was discovered on the asteroids. The chemical components appear isolated and unlinked, failing to follow biological pairing rules like Chargaff's rule, which indicates they formed through non-biological chemical reactions rather than living processes.

During the early formation of the solar system hundreds of millions of years ago, Earth experienced a heavy bombardment of carbonaceous asteroids similar to Ryugu and Bennu. These incoming space rocks delivered a steady supply of amino acids, sugars, ammonia, and salts before the planet even possessed a stable crust. Rather than having to invent its own molecular alphabet from scratch, early terrestrial life likely found the necessary ingredients already written out on the ground.