About space organics on comets and in general

On November 12, a descent vehicle Philae sat on the surface of comet 67P / Churyumov-Gerasimenko. He worked for about 60 hours, and managed to conduct preliminary research. One of the devices managed to register organic compounds, which they wrote about in an official press release .

This news made noise in the media and there were questions like "What, did you find a foreign life?" Decided to sort this question in more detail.

Let's start with the origins: what is "organic".
In everyday life, it is generally accepted that this is something directly related to the vital activity of organisms, i.e. life, but in science the concept is broader. Moreover, in science there is no unequivocal definition of what is, organic. First of all, carbon is necessary for organics. It can create an infinite number of compounds, and if hydrogen atoms participate in them, then such a substance is unambiguously considered organic. But there are several compounds that are not hydrocarbons, but, nevertheless, they relate to organic matter simply historically, by tradition. But we will continue to talk only about hydrocarbons, because it is them who most likely found Philae on a comet.
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COSAC gas analyzer aboard Philae.

Why did I not immediately hurry to tell about this sensational news?
Because organic matter (hydrocarbons) on a comet is not new. Moreover, it is not new and organic in meteorites that fall to Earth.

One of the simplest organic compounds in bulk in the solar system is methane. On Jupiter, for example, the mass of methane is approximately equal to the mass of the entire planet Earth. On the satellite of Saturn, Titan, its smaller, but enough to fill several seas, rivers and clouds, which are regularly shed methane rain.



Only on Earth, it is believed, methane has a biogenic origin - the result of the vital activity of microorganisms that decompose more complex organic compounds. It is considered so because in our atmosphere too much oxygen, which oxidizes methane. However, I dare to suggest, sooner or later, they will prove a non-biological origin of at least some of the methane reserves of the Earth. (And this assumption is not paid for by Gazprom, and is in no way connected with the hydride Earth hypothesis, if you understand what I mean;).

On comets there is also methane in the composition of those volatile compounds that evaporate as the comet approaches the Sun. Methane was also recorded on Mars, but in such insignificant concentrations that the question is still open. Curiosity, for example, did not catch it .



But methane is like that, flowers. Organic matter flies in the Solar System and more interesting. The first hints of organic compounds in the composition of the comet, were obtained in 1986, in the study of Halley 's comet by a group of spacecraft, including the Soviet "Vega".

Later, in 1996, during remote sensing from the Earth by infrared and radio telescopes, comet C / 1996B2 Hyakutake detected methanol, methyl cyanide, hydrogen cyanide, formaldehyde, methane, ethanol, and ethane emissions.

Finally, Stardust’s mission was able to deliver particles of cometary dust to Earth. As it turned out, comet 81P / Wild 2 was far from being as simple as expected from the comet. The results of the analysis of the extracted dust led to some rethinking of what comets are. Previously, it seemed that comets and asteroids are separate bodies that were formed in various ways in different regions of the protoplanetary cloud. Now it turned out that the dust particles of comets are almost identical to the composition of carbon-containing C-class meteorites.



These same meteorites, especially the CI, CM, and CR groups, contain a rich set of complex organic compounds, including purine and pyrimidine nitrogenous bases, which in terrestrial organisms are structural units of information storage in RNA and DNA. It is characteristic that these meteorites even look like coal, for which they are called, often "carbonaceous". Comet nuclei also have a very dark color.



A study of carbon meteorites revealed a whole range of various amino acids and complex organic compounds. Moreover, scientists emphasize that their discovery is not the result of contamination of samples on Earth. This was established for a number of factors: some of the amino acids found are not formed on Earth; meteorites picked up in the ice of Antarctica and in the desert of Australia did not demonstrate the difference in the content of hydrocarbons; the isotopic ratios of light hydrogen and deuterium in molecules differed from terrestrial types.



Today, scientists have come to the conclusion that some asteroids that are currently found in the solar system are “sleeping” comets or cometary nuclei that have exhausted their volatile compounds or have stored them deep beneath the surface.

Another unexpected fact, though not directly related to organic matter, is that both C-class meteorites and particles of cometary dust contain minerals that were formed at high temperatures above 1000 degrees Celsius. This is not consistent with the early hypothesis that comets were formed on the edge of the solar system during the condensation of gases. That is why not only organics is interesting, but in general everything that our “Filka” child found on 67P / Churyumov-Gerasimenko, and how it is necessary to rewrite the textbooks after interpreting the data he received.