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Remnants of vitamin B3 and uracil, key compounds for life, found on asteroid without contact with Earth

In June 2018, after three and a half years of travel, the investigation hayabusa2 The Japanese Space Agency (JAXA) has reached the asteroid Ryugu, which is tens of thousands of kilometers away. After taking samples, the probe dropped a capsule with valuable loot in the Australian desert in December 2020. The results of the analysis of these samples, protected from contact with the Earth, were published today. They have two basic components for life: uracil, one of the units that make up RNA – the molecules that contain the instructions for the construction and operation of living organisms – and also vitamin B3 or niacin, an important agent for the metabolism of living organisms.

Uracil was discovered for the first time in history, A Nucleobase, in a sample taken from an asteroid. discovery Published in this Tuesday’s Journal Communications of nature.

There are several theories about how the ingredients are made call Primitive soup from which life arose about 3.8 billion years ago (although even this dating is disputed). “The present study strongly suggests that such molecules of prebiotic interest commonly formed on carbonaceous asteroids, including Ryugu, and reached early Earth,” the authors note in their paper.

Scientists have already found nucleobases and vitamins in some carbon-rich meteorites, but the question has always been whether they were contaminated by exposure to the terrestrial environment. “Since the ship hayabusa2 By collecting two samples directly from the Ryugu asteroid and delivering them to Earth in sealed capsules, contamination can be ruled out,” he explains. in a press release Yasuhiro Oba, Hokkaido University professor and project coordinator.

This does not mean that life came to Earth from space, but rather that the presence of these ingredients may have played a role in the origin of life.

Michael New
NASA astrochemist

He and his colleagues used a recently developed small-scale analytical technique to analyze the samples. In addition to uracil and niacin, they discovered other organic molecules (a selection of amino acids, amines and carboxylic acids). The same group of researchers had already found them in meteorites that had fallen to Earth, but their discovery in virgin samples strengthens the theory of an extraterrestrial origin.

“This work confirms what we thought before we collected parts of the asteroid and brought them back to Earth for analysis: the mineral and organic composition of the Ryugu asteroid is very similar to that of some classes of meteorites, the so-called Carbonaceous chondrites“, says NASA astrochemist Michel Nuevo to

This independent expert evaluates the work of his Japanese colleagues: “The presence of the main components of life in meteorites, and now in the asteroid Ryugu, supports the scenario when these compounds were brought to the surface of the Earth via asteroids or fragments. Asteroids, which we call meteorites. This does not mean that life came to Earth from space, but that the presence of these ingredients may have played a role in the origin of life.”

Asteroids like Ryugu are made up of intact material from the formation of the Solar System 4.5 billion years ago. The authors suggest that these compounds may have been formed by photochemical reactions of interstellar ice in space, which subsequently led to their introduction into asteroids during the formation of the Solar System. Ultraviolet rays and cosmic radiation can change them over millions of years.

“The Million Dollar Question”

The question remains whether life on Earth could have emerged as it did without the contribution of organic compounds carried by meteorites.

Michel Nuevo is categorical: “This question will be a Nobel Prize.” The short answer is that we don’t know. We do not know how life began, at what point “non-living” materials became “living”. Therefore, it is very difficult to know what role all the ingredients and conditions that we think were present on the early Earth played in the origin of life. It is not yet clear whether life began in the oceans near hydrothermal vents or in warm basins undergoing desiccation/rehydration cycles. What we do know is that asteroids and comets contain organic compounds inherited from the molecular cloud that formed the solar system. These organic materials reached the planets, including Earth, through meteorites, and it is likely that meteorite impacts were more common in the early stages of the formation of the solar system (…) how these organic compounds began to interact and ended. How to replicate and evolve ourselves is the million dollar question we don’t know the answer to.”

In an effort to shed new light on the origins of life on Earth, NASA launched the OSIRIS-Rex probe in 2016 toward the asteroid Bennu, where it arrived in December 2018. The probe is scheduled to return next September.

“The amount of material that OSIRIS-REx is expected to return is far greater hayabusa2So it will be interesting to see what the Bennu samples confirm or not, as Bennu and Ryugu are believed to have very similar compositions,” Nuevo points out.

His colleague Yasuhiro Oba also hopes for NASA’s mission: “The discovery of uracil in the Ryugu samples reinforces current theories about the origin of nuclear bases on the early Earth. NASA’s OSIRIS-REx mission will return samples of the asteroid Bennu (…) and a comparative study of the composition of these asteroids will provide more data to support these theories.”

“big news”

talks to SMC Spain, Angel Menor Salvan, a biochemist and astrobiologist at the University of Alcalá, reiterates that “essential questions” about the origin of life on Earth remain unanswered. He calls the study “great news” but explains that the results of this study “do not at all” suggest that the contribution of organic matter from space was necessary for the origin of life on Earth. “This is a misinterpretation that the media often makes when presenting these types of results,” he says.

He also adds that this paper “does not prove any hypothesis Panspermia, nor does it suggest that life or its components must have come from space or that meteorite impact was necessary for it. The fact that there is uracil in the asteroid does not contribute to the understanding of how life arose. The apparent paradox is that, for this reason, it is a very interesting job. ”

Something more possible is Izaskun Jiménez-Serra, CSIC Senior Scientist at the Center for Astrobiology in Madrid and a specialist in the chemistry of prebiotic molecules in the interstellar environment. Jiménez-Serra also said in a statement with SMC Spain that this is an “exciting” discovery that shows that uracil, one of the nucleobases of RNA, can be synthesized in space. “This implies that significant amounts of uracil could have been present on the early Earth as a result of meteorite impacts.” Late heavy bombardment4,100 to 3,800 million years ago, leading to the first biochemical processes that led to the origin of life.”

Source: El Diario





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