The sugars that make up RNA and DNA, the only elements not found in previous analyses, have now been confirmed in the Bennu samples.
The only ingredient essential for life that had not yet been found on Bennu is now there: traces of various types of sugars were found in samples from the Near Earth asteroid visited in October 2020 by the NASA OSIRIS-REx mission, when the space rock was 320 million km from Earth.
Since the return of the capsule with its precious cargo in 2023, various analyzes had already established the presence, in the rocks of Bennu, of the elements necessary for life. However, sugar was missing, which is necessary to hold together the structure of the molecules at the basis of living things, RNA and DNA.
Previous episodes: what had been discovered about Bennu so far
Since the 121 grams of Bennu dust were returned by OSIRIS-REx, they have been divided among various laboratories around the world capable of analyzing them. The first studies shortly after the return had revealed the presence of water, carbon and various organic molecules in the samples; at the beginning of this year, the discovery of various amino acids, many of which are present in terrestrial biological processes, ammonia and all five nitrogenous bases that make up RNA and DNA was confirmed in Bennu crumbs.
There was no trace, until now, of the sugars that make up the skeleton of the nucleotides, i.e. the basic blocks, of RNA and DNA, i.e. ribose for RNA and deoxyribose for DNA. Until the new study, just published on Nature Geoscience.
On the asteroid Bennu there are ribose and other sugars
A team of scientists from Tohoku University in Sendai, Japan, chopped up and mixed a small portion of Bennu rocks with acids and water, and used gas chromatography-mass spectrometry to separate and analyze the compounds. The analyzes revealed the presence of ribose in the asteroid samples – therefore of the structural component of RNA, together with other sugars such as xylose, arabinose, glucose and galactose, but not deoxyribose.
Scientists believe the sugars may have formed in the same pools of brackish water hypothesized on Bennu’s parent celestial body, the aqueous frosts in which the complex molecules traced so far are thought to have originated. An important fact, because those same salt water pools would also be found on Saturn’s moon Enceladus and on the dwarf planet Ceres. The ingredients underlying life would therefore be abundant in the Solar System and asteroids could have transported them to Earth and other celestial bodies, such as Mars.
Two highly anticipated confirmations
The presence of sugars and other molecules fundamental for life had already been confirmed in the past on meteorites that fell on Earth, for which however the possibility of contamination following the impact could not be completely excluded.
Having found sugars also on the samples of Bennu, which arrived intact, is a confirmation of the validity of the previous discoveries.
Furthermore, the absence of deoxyribose, the sugar that gives structure to DNA, on Bennu, supports the idea of the “RNA world”, according to which the most ancient forms of life on Earth, long before the development of DNA and proteins, consisted of RNA molecules that played both the role of containers of genetic information and that of catalysts of chemical reactions.
