Where did the first building blocks of life come from? A possible answer provide rehearsals by the Asteroid Bennu, which the NASA room probe Osiris-Rex brought back to Earth in 2023. Now the first analysis results are available. Among other things, they reveal that the asteroid material contains more than 10,000 different organic molecules. These include 33 amino acids and all five nucleotide bases found in the earthly DNA and RNA. In analyzes of the inorganic components of the Bennu samples, the researchers also demonstrated eleven different salt minerals, including some very rare mineral shapes on earth. They must have arisen from salted liquids and indicate that Bennu’s mother sky body either came from the water -rich outer solar system or accumulated ice -covered dust grains from this zone, as the researchers explain.
It was long assumed that more complex organic molecules such as DNA building blocks, proteins or amino acids were created in certain earthly “life craduates”-for example on lower seas casting pacles, hydrothermal porpes or in rock spores. In the meantime, however, there are increasing indications that the origin of the first building blocks could also be in space – in asteroids and comets that hit the planet in the early days of the earth. Because analyzes and space missions show that many organic molecules can also arise under space conditions. On the comet 67p/Churyumov-Gerasimenko, the ESA-Landesonde showed 16 different organic compounds, including precursors of sugar, amino acids, peptides and nucleotides. DNA bases have also been found in meteorite samples. In addition, laboratory experiments suggest that the ice-crossed dust grains in comet kernels and interstellar dust clouds offer favorable conditions for the chemical synthesis of peptides, components of the DNA sugar frame and other components of organic molecules.
Amino acids from asteroid Bennu
More information about the cosmic molecular formation now provides samples of the near -earth asteroid (101955) Bennu. This asteroid, which weighs around 500 meters tall and 60 million tons, revolves around the sun on one from just within the earth’s railway to Mars and is considered a relic from the early solar system. Telescopic observations also suggested that Bennu is one of the type B saints-carbon-rich chunks with an increased proportion of water and other fleeting substances. Such asteroids would therefore be good candidates as “suppliers” for the early building blocks. In 2016, NASA sent more about the Asteroid Bennu and its composition, the Osiris-Rex spacecraft in 2016. After its arrival in 2018, the probe initially collected data from the orbit around the chunk. In 2020 the crucial step followed: Osiris-Rex approached the surface of Bennu to such an extent that their robotic arm was able to take samples from its surface and the material whirled up with a small demolition. In 2023 the spacecraft then brought the 120 grams of asteroid material back to earth.
Now an international team under the direction of Daniel Glavin and Jason Dworkin from NASA Goddard Space Flight Center has published the results of the rehearsal analyzes. One of the research groups had specifically examined the organic components of the asteroid material – and discovered tens of thousands of chemical compounds based on hydrocarbon. Among them were also several essential building blocks: “We discovered amino acids, amine, formaldehyde, carboxylic acids, polycyclic aromatic hydrocarbons and nitrogen -containing heterocycles, as well as around 10,000 nitrogen -containing chemicals,” report Glavin and his colleagues. Among the 33 proven amino acids were 14 of the 20 for earthly life and protein production essential amino acids such as glycine, asparagine or tyrosine. “In addition, we identified 19 non-protein amino acids,” said the team. These do not occur in the genetic code and in the proteins of earthly living beings. Many amino acids from the Bennu samples were also a mixture of left and right-handed variants- as a so-called racemat. In doing so, they differ significantly from the amino acids created by earthly living beings, because they are all left -handed. “This contradicts the hypothesis, according to which the life based on left -handed proteins on earth was shaped by an imbalance that is also present in the solar system,” the scientists write. At the same time, this confirms the extraterrestrial origin of this molecules.
DNA bases and inorganic salts
In addition, the researchers also discovered nucleotides in the rehearsals-the molecules that form the “sprouts” as DNA bases in the knitting conductor-shaped inheritance molecule. Glavin and his colleagues were able to demonstrate all five DNA and RNA bases occurring in organisms- Adenin, Guanin, Cytosin, Thymin and this only occurred in the RNA. Some of these nucleic acids as well as other nitrogen -containing molecules have already been found in meteorites and in rehearsals of the asteroid Ryugu – but less numerous and diverse. “The differences in the frequency and complexity of nitrogen heterocycles between Bennu and Ryugu could reflect the different surroundings that these asteroids were exposed to in space,” explains co-author Yasuhiro Oba from the University of Hokkaido. The high content of ammonia, water-soluble organic compounds and unusual nitrogen isotope values is also characteristic of Bennu. “This could indicate that the celestial body, whose fragment is Bennu, has accelerated ice from the outer solar system,” the researchers write. Only then did this object move into the inner solar system. Alternatively, ice -rich dust from this outer zone could also have been scraped inwards and only deposited on the mother’s body there.
In a second specialist article, a team led by Tim McCoy from the National Museum of Natural History in Washington DC reports about inorganic salts and minerals that were found in the asteroid samples. “These include sodium -containing phosphates and sodium -rich carbonates, sulfates, chlorides and fluorides,” said the researchers. These salt-containing minerals indicate that there must have been salt-containing liquids on Bennu’s mother-sky base. When this brine evaporated, the salts crystallized and formed these minerals. Among them are connections such as the sodium hydrogen carbonate trona, which also occurs in earthly salt lakes, and also rare sodium fluoride villiaumit. They have now been detected for the first time on an extraterrestrial heavenly body. According to the scientists, this supports assumptions, according to which such salt -containing liquids could still occur in larger asteroids such as the dwarf planet Ceres and inside ice cream monds such as the Saturnmond Enceladus. “Together our analyzes brought us a big step further to understand how asteroids like Bennu developed and how they could have contributed to making the earth with life-friendly,” says co-author Sara Russell from the Natural History Museum in London.
Source: Daniel Glavin, Jason Dworkin (Nasa Goddard Space Flight Center, Greenbelt) et al., Nature Astronomy, DOI: 10.1038/S41550-024-02472-9; Tim McCoy (National Museum of Natural History, Washington DC) et al., Nature, DOI: 10.1038/S41586-024-08495-6