Key building block for life discovered on distant asteroid Ryugu — and it could explain how life on Earth began

Scientists have found uracil, one of the key building blocks for RNA, on the 200 million-mile-distant asteroid Ryugu

For the first time, scientists have found one of the key building blocks for RNA on an asteroid in space. The discovery indicates that the blueprints for life may have been brought to Earth from beyond our planet, and that rudimentary forms of life could exist elsewhere in the solar system. 

Japanese scientists performed the new analysis on a sample taken from the diamond-shaped asteroid Ryugu. The researchers found uracil, one of the five nucleobases that make up our genetic code, along with vitamin B3 and a number of other organic molecules on the space rock's surface.

An animation of asteroid Ryugu made with images from JAXA's Hayabusa2 mission. (Image credit: JAXA/University of Tokyo/Kochi University/Rikkyo University/Nagoya University/Chiba Institute of Technology/Meiji University/University of Aizu/AIST)

Previous analyses of meteorites found on Earth revealed that the fallen space rocks contained the five nucleobases essential for building life as we know it, but scientists were unsure if they were there before they plummeted to Earth or got onto the meteorites by contamination with our atmosphere. But the analysis of Ryugu's contents, which were scraped from the asteroid's surface before being launched back to Earth, has provided a significant clue that the cosmos could be teeming with life-sparking molecules. The researchers published their findings Mar. 21 in the journal Nature Communications(opens in new tab). 

"As long as uracil and other nucleobases are present in space, it means the ingredients for nucleic acids [DNA and RNA] are present in that environment," lead author Yasuhiro Oba(opens in new tab), an astrochemist at Hokkaido University in Japan, told Live Science in an email. "In my personal opinion, it is difficult to exclude the possibility that some forms of life are present in extraterrestrial environments."

The five nucleobases — adenine, guanine, cytosine, thymine and uracil — combine with ribose and phosphate to form DNA and RNA, the ladder-like structures that make up the genetic code of all life on Earth. It is from this code that cells are manufactured: DNA unzips and gets transcribed into RNA; the RNA makes proteins; and the proteins in turn act as microscopic machines that build and maintain cells while also creating more copies of DNA. 

To make the first-of-its-kind detection, the Japan Aerospace Exploration Agency (JAXA) sent the Hayabusa2 spacecraft on a 200 million-mile (322 million kilometers) journey to Ryugu, a carbonaceous asteroid crammed with carbon-rich organic matter. Much of Ryugu's contents, which are loosely piled together as a spinning collection of rubble, likely originated from the same nebula that gave birth to the sun and our solar system's planets roughly 4.6 billion years ago, according to the researchers.

After touching down on the asteroid in 2018, Hayabusa2 scraped about 0.2 ounces (5.4 grams) from Ryugu's surface, before stowing the material in an airtight container and launching itself back to Earth on a fine-tuned trajectory. Other building blocks for life, including 15 different amino acids, were also discovered inside the returned sample.

How life's blueprints first formed on Ryugu, or in the interstellar cloud that would later birth it and the rest of our solar system, isn't well understood. The researchers believe amino acids and nucleotides could have been made when interstellar ice was zapped with intense cosmic rays, breaking down the simple molecules trapped within and reconstituting them in more complex configurations. After becoming trapped on asteroids like Ryugu, these molecules may have eventually hitched a ride to Earth via meteorite impacts, where they sparked the first stirrings of life in primordial oceans.

Ryugu is not the only space rock under investigation. In 2021, NASA's OSIRIS-REx spacecraft collected a rock sample from another diamond-shaped asteroid, named Bennu. When the sample returns to Earth in September, signs of organic matter contained within it could provide scientists with important clues about the evolution of the solar system and its materials, as well as hints of how life emerged from them.