Asteroid Bennu carries all ingredients to kick-start life as we know it

All the essential ingredients to kick-start life as we know it have now been found in samples from the asteroid Bennu. This shows that asteroids could have delivered all the prerequisites for life to Earth – and perhaps elsewhere.

In 2020, NASA’s OSIRIS-REx mission extracted samples from Bennu, an asteroid that was orbiting the sun hundreds of millions of kilometres away, between Mars and Jupiter. The mission returned the samples to Earth in 2023. Since then, small amounts of the 121 grams collected have been sent out to labs across the globe for analysis, so specialists in detecting each type of biological compound could set to work.

The first studies revealed the presence of water, carbon and several organic molecules. Next came the detection of amino acids, formaldehyde and all five of the nucleobases found in RNA and DNA, as well as phosphates. However, this isn’t quite enough to put together the molecules that carry genetic information. The rungs of the ladder of RNA and DNA contain a sugar, which is ribose in RNA and deoxyribose in DNA – and that was missing from the first analyses of the Bennu material.

Now, Yoshihiro Furukawa at Tohoku University in Japan and his colleagues have crushed a small share of the sample and mixed it with acid and water. Then they used gas chromatography-mass spectrometry to separate and identify the components in the mix.

This revealed the presence of ribose, as well as other sugars, including lyxose, xylose, arabinose, glucose and galactose – but not deoxyribose.

“This is a new finding of sugars in extraterrestrial materials,” says Furukawa, who adds that almost all life relies on glucose in its metabolism.

“This is such a brilliant result from the OSIRIS-REx mission,” says Sara Russell at the Natural History Museum in London, who wasn’t part of the team, but who also works on Bennu samples. “The one missing ingredient was the sugar, which has now been reported, so now all of the ingredients of RNA are known to be in primitive asteroids.”

Furukawa and his colleagues believe that the sugars formed from brines containing formaldehyde in the parent asteroid from which Bennu came, which is thought to have carried more fluid and featured more reactions.

“Earlier this year, we reported finding salts in the returned sample, and suggested there would have been briny pools of water on Bennu’s parent body,” says Russell. “Such environments would have perfect places to cook up the complex organics that we see in Bennu.”

There is evidence for brines on Saturn’s moon Enceladus and the dwarf planet Ceres, which suggests that the ingredients for life may be abundant in the solar system, says Russell.

Furukawa’s work has previously detected ribose and other sugars in meteorites found on Earth, but he says there was always a worry that these compounds could have made their way into the rock as a result of contamination once they reached Earth. “This finding in the Bennu sample guarantees that these results were true,” he says.

The new work shows that asteroids really could have delivered all the ingredients necessary for life to Earth or to other bodies in the solar system, like Mars, says Furukawa. It also supports the RNA world hypothesis for the origin of life because ribose was found, but deoxyribose wasn’t.

This idea proposes that the earliest life on Earth, long before the advent of cells or DNA-based life, consisted of RNA molecules that contained genetic information and could replicate.