Asteroid Bennu: NASA detects life-linked sugars, mysterious ‘space gum’ and ancient stardust

Sugars essential for DNA and RNA
According to a team of scientists led by Yoshihiro Furukawa of Tohoku University in Japan, samples brought back from Bennu contain five-carbon sugar ribose. Also, for the first time, a sample collected from outer space was found to contain six-carbon glucose. While these findings do not confirm the existence of life, the recent and previous findings show how building blocks of biological molecules are spread throughout the solar system.
“All five nucleobases used to construct both DNA and RNA, along with phosphates, have already been found in the Bennu samples brought to Earth by OSIRIS-REx. The new discovery of ribose means that all of the components to form the molecule RNA are present in Bennu,” said Furukawa.
Researchers believe that the presence of ribose and the lack of deoxyribose support the “RNA world” hypothesis, as primary forms of life relied on RNA to store information and perform chemical reactions necessary for survival. Interestingly, samples from Bennu also contain the sugar glucose molecule, one of the most common forms of food on Earth.
Never-before-seen gum-like substance
The second paper, published by NASA’s Ames Research Center and the University of California, Berkeley, reveals that the asteroid also has a never-before-seen gum-like material that was presumably formed in the early days of the solar system.
The ancient “gum” was once soft and flexible and consisted of nitrogen and oxygen materials, which scientists say may have helped some of the chemical precursors that helped form life on Earth. Studying the substance might also help us understand how life started and if it exists outside our planet.
According to Scott Sandford, Bennu is an ancient asteroid formed by materials in the solar nebula, a huge cloud of gas and dust that formed the solar system as we know it. But as the asteroid started to heat up due to radiation in space, a compound known as carbamate was formed. Somehow, the water-soluble substance polymerised by reacting with other molecules to form bigger and more complex chains, hinting that it was synthesised before the asteroid started to warm up.
“With this strange substance, we’re looking at, quite possibly, one of the earliest alterations of materials that occurred in this rock. On this primitive asteroid that formed in the early days of the solar system, we’re looking at events near the beginning of the beginning,” says Sandford.
Scientists say they used an infrared microscope to study unusual, carbon-rich grains containing abundant nitrogen and oxygen, and started doing what Sandford calls “blacksmithing at the molecular level.”
Using super-thin layers of platinum, they reinforced the particle and welded it to a needle made from tungsten to lift it and further shaved it using a beam of charged particles. When it was finally a thousand times thinner than human hair, its composition was studied using electron microscopes and X-ray spectroscopy.
When the substance was studied, it was found that the grain was deposited in layers on grains of ice and minerals in the asteroid. As it turns out, the gum-like substance was flexible, similar to soft plastic and bent and dimpled when pressure was applied. However, exposure to space radiation made it brittle.
Supernova dust
Bennu samples also contained an abundance of supernova dust. These presolar grains are basically dust from stars that existed before the solar system. Compared to other space rocks, the samples had six times more supernova dust, hinting that the asteroid’s parent body was formed in the protoplanetary disk, which is full of dust from dying stars.
And while Bennu’s parent asteroid underwent extensive alteration by fluids, it looks like the space rock still has pockets of less-altered material.
“These fragments retain a higher abundance of organic matter and presolar silicate grains, which are known to be easily destroyed by aqueous alteration in asteroids. Their preservation in the Bennu samples was a surprise and illustrates that some material escaped alteration in the parent body. Our study reveals the diversity of presolar materials that the parent accreted as it was forming,” says Ann Nguyrn, a member of NASA’s Johnson Space Center in Houston who analysed the asteroid.