Asteroid Hosts All Ingredients for DNA and RNA. Did We All Come From Space?

Samples collected from the asteroid Ryugu contain the four genetic “letters” of DNA.

08 Apr 2026, 14:04 by Matthew R. Francis · ZME Science

The asteroid Ryugu is seen by the Hayabusa2 spacecraft from a distance of 6 kilometers. Credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST

The basic ingredients for life as we know it are common in the cosmos. Scientists are still learning which of those ingredients were present on primordial Earth, and how they combined to make life remains an unsolved mystery. However, many researchers now think many of the molecules necessary for life were already present in the nebula that grew into our solar system, which would mean the components for all living things came from space.

A recent study published in Nature Astronomy provides strong new support for that hypothesis. Scientists identified all five nucleobases—the chemical “letters” that make up DNA and RNA—in a sample taken from asteroid Ryugu (ree-oo-GOO). The Japan Aerospace Exploration Agency’s Hayabusa2 spacecraft brought the sample to Earth in 2020 for laboratory study.

“Detecting all five nucleobases in extraterrestrial materials shows that the full set of these key molecules can form in space,” said Toshiki Koga, a biogeochemist at the Japan Agency for Marine-Earth Science and Technology in Yokosuka and lead author of the new study. In an email interview, he wrote, “Together with the results from the asteroid Bennu, this strengthens the idea that these molecules may be widespread in primitive asteroid materials.”

“Primitive” in this sense means asteroids and meteorites that were relatively untouched by processes that shaped the solar system, such as high heat and successive collisions. This category, known as carbonaceous chondrites, includes Ryugu, Bennu, and famous meteorites such as Murchison, which landed in Australia in 1969. Scientists have identified amino acids—the chemical building blocks of proteins—as well as nucleobases in carbonaceous chondrites.

But the discovery on Ryugu is the first time researchers have found all five nucleobases in one place in roughly equal quantities. This lends strong support to the idea that prebiological molecules were present, perhaps even common, in the solar nebula that condensed into the Sun and the planets 4.5 billion years ago.

“We look at samples that have been returned from these missions [like Hayabusa2] and that confirms things we found in Murchison,” said Áine O’Brien, an astrobiologist at the University of Glasgow who was not involved with the Ryugu study. Because carbonaceous chondrite meteorites likely were broken off of asteroids like Ryugu (possibly even Ryugu itself), they could tell an important part of our origin story. “Could meteorites like Murchison have been what brought the ingredients for life to Earth in the first place? That is the point of the entire field of astrobiology.”

The Letters of Life

The canonical nucleobases are the purines adenine (A) and guanine (G) and the pyrimidines cytosine (C), thymine (T), and uracil (U). The sequence of A, G, C, and T in DNA encodes genetic sequences, while U takes the place of T in RNA. These organic molecules are also components of ATP (adenosine triphosphate, the energy courier within cells) and other essential biomolecules. In other words, nucleobases are fundamental to all biology as we know it, but they themselves are relatively simple molecules.

Researchers found more purines than pyrimidines in Murchison but measured the opposite in the asteroid Bennu and the meteorite Orgueil, which landed in France in 1864. However, Koga and his colleagues found nearly equal amounts of all five canonical nucleobases in Ryugu, which has potentially exciting implications for the abundances of these molecules in the solar nebula.

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In particular, they noted that the ratio of purines to pyrimidines correlates inversely with the amount of ammonia in samples: The more purines there are relative to pyrimidines, the less ammonia is present and vice versa. That in turn hints at the processes by which nucleobases formed before the solar system came to be.

Foreign Contaminant

Grains of material from the asteroid Ryugu, seen here, were collected by the Hayabusa2 spacecraft and returned to Earth. Credit: JAXA

“These molecules are also difficult to identify because they are present only in trace amounts,” Koga warned, noting that other prebiological molecules like amino acids are far more common and easier to isolate. Another challenge is contamination because biomolecules are everywhere on Earth. The researchers isolated the sample from Hayabusa2 in an extremely clean facility, then performed comparison measurements with “blanks” made of sea sand and serpentine from Earth to ensure the nucleobases were actually from Ryugu.

But finding even tiny amounts of nucleobases in small samples actually reinforces the strength of the discovery.

“The fact that we’re able to detect these things at that concentration in such a small sample does indicate we would expect to find these things in other asteroids,” O’Brien said. She added that Ryugu and Bennu were chosen as targets for sample collection because they’re carbonaceous chondrites, like the Winchcombe meteorite that provided much of the data for her own research. “We’re seeing a diverse suite of organics and it’s taking us back in time billions of years.”

Koga and his team also found molecules, such as hypoxanthine and xanthine, that are closely related to nucleobases. These molecules are not themselves genetic materials but are extremely interesting to astrobiologists because they can play a part in building DNA and RNA—or other molecules known as XNA that might be the basis for life elsewhere in the cosmos.

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“Our results support the idea that chemically diverse nucleobase analogues were available, which could be relevant when considering alternative pathways for the origin of genetic systems,” he said. Every data point reinforces the conclusion that nucleobases—along with amino acids—were part of the primordial solar system, seeding early Earth with the ingredients for life as we know it. “These molecules may have been relatively common in primitive materials in the early solar system and could have been widely available for delivery to the early Earth and other planetary bodies.”