This photograph was taken from the navigation room Rosetta March 25, 2015, at a distance of 86.6 km from the nucleus of comet 67P . these days the ROSINA instrument carried out a survey of glycine in the comet’s coma. Credits: ESA / Rosetta / NavCam
components that we feel are crucial for the origin of life on Earth were detected on comet 67P / Churyumov-Gerasimenko, the object of study of the probe Rosetta ESA for about two years. Among the detected ingredients appear the amino acid called glycine, which is commonly found in proteins, and phosphorus, one of the key elements of DNA and cell membranes.
The scientific community has long debated the possibility that water and organic molecules have been brought to Earth by asteroids and comets, and that by doing so the small bodies of the solar system have provided us with some of the key building blocks for the emergence of life. If it is true that some comets and asteroids have been shown to contain water with a composition similar to that of Earth’s oceans, it is also true that Rosetta has found significant differences in the composition of the water 67P, fueling the debate on the genesis of water on Earth .
the new results collected show that comets may still have played a key role in the manifestation of life as we know it. Amino acids are organic compounds containing carbon, oxygen, hydrogen and nitrogen, and form the basis for the proteins, then play a biologically fundamental role. Traces of the simplest of the amino acids, namely glycine, were found in the samples brought back to Earth in 2006 by the Wild-2 comet, object of study of NASA’s Stardust mission. However, the high probability of terrestrial contamination of the samples had rendered the results of analysis rather weak. What he got Rosetta, however, are surveys of glycine directly in the canopy of his comet .
“This is the first unambiguous detection of glycine in a comet,” he says Kathrin Altwegg , principal investigator of the ROSINA instrument that performed the measurements and lead author of the study published in Science Advances . “At the same time we also detected the presence of other organic molecules, which can be precursors of the glycine, providing clues about the ways in which this amino acid may have formed”
The measurements were carried out before the comet reached its closest approach to the Sun, called perihelion, which took place in August of 2015. the first survey was obtained in October 2014, while Rosetta was located 10 km away from the comet. The next opportunity arose during a close flyby in March 2015, when the probe was located at 15-30 km from the comet’s nucleus. Glycine has also been observed on other occasions, associated with emissions of jets during the previous month at perihelion, when Rosetta was at more than 200 km from the nucleus, and was surrounded by large amounts of dust.
The ROSINA instrument onboard Rosetta found are considered essential ingredients for life as we know it on Earth 67P inside the comet’s coma. on the top right the amino acid called glycine detection, bottom right a key element for all living beings, or phosphorus. top left one probe scheme, with stated the position of the ROSINA instrument, in low orbit around the comet Rosetta. at the center of the image collection March 25, 2015 from the navigation room. Click on the image to enlarge. Credit: ESA probe / ATG medialab; comet: ESA / Rosetta / NavCam – CC bY-SA 3.0 IGO; data: Altwegg et al. (2016)
“the glycine is the only amino acid known to be able to be formed without water liquid, and the fact that we observe it together with the precursor molecules and the dust suggests that it is formed within the interstellar dust grains or by irradiation of frozen ice by ultraviolet light, to then be preserved for billions of years in the comet, “adds Altwegg .
La glycine is transformed into gas only when it reaches temperatures of around 150 ° C, and this means that for most of the lifetime of the comet the amount of glycine released from the surface is infinitesimal, given the low temperatures. This explains why Rosetta was able to detect only during short time windows.
Another interesting survey described in the article is that of phosphorus, a key element for all living organisms. For example, we can find it in the structure of DNA and cell membranes, and is used for the transport of energy within cells.
“There is still much uncertainty regarding the chemistry that was present on the early Earth, and there is also, of course, an enormous evolutionary gap to be filled between the arrival of these ingredients with cometary impacts, and the occurrence of life, “says Hervé Cottin , co-author of study. “The most important aspect is that comets have not got to change over the past 4.5 billion years, and then provide us with a direct access to some of the ingredients that are probably finished in the great prebiotic soup that led to life on Earth “.
” the company of organic molecules already identified by Rosetta, now joined the exciting confirmation of key ingredients such as glycine and phosphorus, strengthens our hypothesis that comets they have the potential to provide the key elements for prebiotic chemistry, “says Matt Taylor , scientist Rosetta mission. “Being able to show that comets contain the most primitive material in the solar system and may have transported the fundamental elements for life on Earth is one of the main objectives of the Rosetta mission, so we are particularly pleased with this important result.
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source: Media INAF | Written by Elisa Nichelli
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