Meteor impacts could have provided Earth with the essential materials for the emergence of life, as a study has shown again: Researchers have detected uracil – a component of the DNA of living organisms – in samples from the near-Earth asteroid Ryugu. In addition to other interesting compounds, they also found the compound nicotinic acid, which is also known as the vitamin niacin and plays an important role in the metabolism of terrestrial organisms. The results thus support the assumptions that some biologically relevant materials were first brought to Earth by carbon-rich meteorites and were implicated in the emergence of life.
They are astronomical time capsules from our solar system’s past: many asteroids are still composed of material that participated in the formation of the celestial bodies of the solar system. What distinguishes these planetary building blocks? For a long time, scientists could only examine samples that fell to Earth to gain insight into this question: meteorites. But there was always the possibility that the components found were contaminated with terrestrial materials or metamorphic products from fallout into the atmosphere.
Sexy mail from space
But that has changed: the Japanese space probe Hayabusa2 collected rock samples from two places during a visit to the asteroid Ryugu, which is about a kilometer across. Sometimes Ryugu gets so close to Earth that a rover visit and return of rock samples were possible. Finally, on December 5, 2020, mail from space has landed in Australia. The precious material has already undergone various investigations. Among others, organic molecules can already be detected in the carbon-rich material. Now scientists around Yasuhiro Aoba of Hokkaido University in Sapporo have investigated the composition of extraterrestrial matter using more detailed research methods than before.
The scientists used a newly developed analysis method that can also handle tiny amounts of material. In the case of Ryugu’s two samples, they were about ten milligrams each. The researchers extracted particles from the material by heating them in water using a special process. The materials were then analyzed using liquid chromatography and high-resolution mass spectrometry in order to use specific patterns to clarify the identity of the components.
Basic subjects in biology
As the researchers report, they have found traces of exciting substances: above all, the compound uracil, which is important for heredity. As a nucleolar base, it forms an information unit of RNA that transmits instructions for the structure and functioning of living organisms. Researchers have also found nicotinic acid, sometimes referred to as vitamin B3 or niacin, an important factor in the metabolism of organisms. “Other biologically relevant molecules have also been found, including a selection of amino acids, amines and carboxylic acids that occur in proteins or in metabolism,” says Ohba.
As the scientist emphasizes, the important aspect of the results is that terrestrial contamination can now be ruled out through the completely aseptic processing of the Ryugu material. “Scientists have found nucleobases and vitamins in some carbon-rich meteorites on Earth in the past, but the issue of pollution from contact with the Earth’s environment has always been raised,” explains Ohba. “Since the Hayabusa2 spacecraft took two samples directly from the asteroid Ryugu and brought them back to Earth in sealed capsules, this can now be ruled out.” In other words: biologically relevant materials were created in the conditions of space.
The authors hypothesize that the compounds were formed from precursor materials by photochemical reactions in interstellar ice, which later agglomerated with dust to form asteroids. Ultraviolet light and cosmic rays can alter molecules over millions of years. Loaded with this special material, it is likely that asteroids also entered the young Earth – with the potential for “fruitful” consequences: “The discovery of uracil in samples from Ryugu strengthens current theories about the origin of nuclear bases on the early Earth,” Ohba says. He now hopes to further confirm this assumption: “NASA’s OSIRIS-REx mission will return samples from the asteroid Bennu this year and a comparative study of the composition of these asteroids will provide more data that can provide further clues.” world.
Source: Hokkaido University, professional article: Nature Communications, doi: 10.1038/s41467-023-36904-3
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