Asteroids are extraterrestrial objects made of rocks, metals and ice that orbit the Sun. Theories suggest that the chemical reactions within them could create some of the elements that are essential to life. In the Proceedings of the National Academy of Sciences (PNAS) on November 18th, scientists confirmed these hypotheses. Indeed, they discovered that meteorites that have hit the Earth, often from asteroids, contain 'bio-essential' sugars.
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Ribose, an essential sugar
According to a NASA press release, several meteorites have been analysed. One had landed in Australia in 1969, the other in North America in 2001. However, they were several billion years old. The researchers had already gone looking for sugar in these celestial objects, without any luck. This time, they used a different extraction method, using hydrochloric acid and water. They finally identified arabinose, xylose... But the most significant discovery was the ribose.
Ribose plays an important role in human biology, particularly in RNA. These molecules, which have many functions in the cell, are made up of a combination of 'ribonucleotides.' They also transmit the messages to our DNA to build proteins in our body. However, a model of the molecular structure of the ribose was found in two carbon-rich meteorites. 'It is remarkable that a molecule as fragile as ribose can be detected in such an ancient material,' says Jason Dworkin, co-author of the NASA study.
Meteorites, the source of life?
The discovery of this sugar also gives scientists a more precise idea of the formation of life: it suggests that RNA evolved before DNA. The latter has long been considered as the 'template of all life.' But the RNA could have additional capabilities. In particular, molecules can replicate without the help of other molecules. Nor did the researchers detect DNA sugars in meteorites. 'RNA coordinates the mechanism of life before DNA,' they concluded.
'Extraterrestrial sugar could have contributed to the formation of RNA on the prebiotic Earth, which could eventually lead to life,' said Yoshihihiro Furukawa, lead author of the study at Tohoku University (Japan). The hypothesis that meteorites may have been contaminated by life on Earth is not ruled out. But their tests showed that this is unlikely: the sugars probably came from space.
This new research adds to the growing list of evidence that meteorites may have led to life on Earth. Last January, other essential ingredients for existence - amino acids, hydrocarbons, other organic matter and traces of liquid water - that date back to the early days of our solar system, were found in two meteorites.
