Comets could have seeded life on Earth, study finds

Ribose, a simple sugar which serves as the backbone of RNA in living organisms, might have originally formed inside comets, a new experimental analysis by scientists at the Institut de Chimie de Nice (CNRS/Université Nice Sophia Antipolis) has revealed.

The researchers, whose work was published Friday in the journal Science, created an artificial comet with the help of colleagues at the Institut d’Astrophysique Spatiale in Orsay, France and found a scenario where the carbohydrate could have formed in cometary ices.

While ribose is a key building block in the genetic material of humans and other life forms, it had previously never been detected in meteorites or comets. By detailing a scenario in which the compound could have formed in cometary ices, the study authors explained that they have come one step closer to fully understanding the origins of RNA, and therefore of life itself.

“Our results suggest that the generation of numerous sugar molecules, including the aldopentose ribose, may be possible from the photochemical and thermal treatment of cosmic ices in the late stages of the solar nebula,” they wrote. “Our detection of ribose provides plausible insights into the chemical processes that could lead to the formation of biologically relevant molecules in suitable planetary environments.”

Comets formed from formaldehyde likely contained ribose, other sugars

Nucleic acids such as RNA and DNA comprise make up the genes of all organisms living on Earth, the researchers explained in a statement. RNA, which is considered more primitive than DNA, is believed to have been one of the first molecules characteristic of life to appear on our planet, and experts have long wondered how the nucleic acid originally formed.

One hypothesis suggests that comets and/or asteroids containing the core components needed to form such molecules once bombarded the Earth – a notion supported by the discovery of  amino acids (the components of proteins) and nitrogenous bases (a component of nucleic acids) in both meteorites and in artificial, laboratory-produced comets. Attempts to use such methods to detect ribose, however, had proven unsuccessful – until now.

As part of their experiments, the French scientists produced an artificial comet by mixing water, methanol, and ammonia in a high-vacuum chamber at temperatures of -200 degrees Celsius. They began by simulating the formation of ice-coated dust grains, then irradiated these base materials with ultraviolet rays to simulate conditions in the molecular clouds in which these grains formed. The sample was then heated up to simulate the comet model approaching the sun.

Using multidimensional gas chromatography and time-of-flight mass spectrometry, the authors analyzed the composition of the artificial comet, successfully detecting ribose and several other kinds of sugar. They believe the diversity and relative abundance of the molecules indicate that they were formed from formaldehyde, a molecule often found on comets.

While the researchers emphasize that this is not confirmation that ribose exists in actual comets, they explained that their work shows that all of the molecules required for the formation of living organisms can be formed in interstellar ice. Furthermore, they said that the results lend additional support to the notion that the organic molecules that gave rise to life on Earth came from comets.

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Image credit: NASA

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