This will help to specific substances.
Scientists have determined what combination of gases may be a sign of the presence of life. A symptom of the existence of life on the exoplanet may be the simultaneous presence of methane, nitrogen, carbon dioxide and water vapor in its atmosphere, report scientists in the journal Science Advances.
To further indicate the presence of organisms may lack carbon monoxide, which is actively consumed by microbes. Made by astronomers of the assessment will help in the search for life beyond Earth, and also in the selection of planet-candidates for further research.
In our galaxy there may exist several trillions of planets, tens of millions of which can be potentially habitable. Since we cannot directly observe the surface of distant celestial bodies, to search for life have to use indirect methods, in particular spectroscopy of the atmosphere. It allows you to know the chemical composition of the atmosphere and to find so-called biomarkers — substances that say that on the planet there may be plants or microorganisms. Today one of the most popular biomarkers include oxygen, ozone, water, methane and carbon dioxide. Each one individually may have a natural origin, while their combination may indicate the life of the earthly type.
On Earth today there is a very strong chemical imbalance in the atmosphere due to the large number of living organisms on its surface. For example, if we turned off all the processes of life, producing oxygen and methane, in a relatively short time in the gas envelope of our planet of these chemicals would simply be left, as they interact with each other and get each other. However, in the Precambrian period, which accounts for about 90 percent of our planet’s history, the diversity of organisms on Earth was significantly smaller, and therefore the composition of the atmosphere had to be different. At the same time, what are the biomarkers in this case, it would point to the habitability of our planet is poorly known.
In the new work, scientists under the leadership of Joshua Kristiansen-Totton (Joshua Krissansen-Totton) calculated, what could be the chemical composition of the system atmosphere-ocean during the Archean, Proterozoic and Phanerozoic (the period, which began 542 million years ago and continuing today). For this they used a special model, which calculates the difference in Gibbs energy between the initial and final States of the system. The Gibbs free energy allows us to establish the fundamental possibility of occurrence of a chemical reaction under specified conditions.
It turned out that a chemical imbalance in okeanicheskie-atmospheric system of the Earth grew as the evolution of life. The largest balance was observed during the Archean, which considerably decreased during the oxygen catastrophe, when the era of the Proterozoic the composition of the air changed dramatically. Other global increase in oxygen that occurred in the Neoproterozoic, has led to a growing imbalance.
If the life of archaea was chemotrophy (chemotrophy organisms that get energy by redox reactions) in the atmosphere has been observed an increased amount of CO2, N2, CH4, and water vapor. In anoxigenic photosynthesis, the chemical imbalance would increase. During the Proterozoic and Phanerozoic on the planet twin of Earth for life signs indicate the simultaneous presence of O2, N2 and liquid water.
The researchers note that despite the availability of other sources of methane, including volcanoes, asteroid collisions, the interaction between water and rocks, large quantities of this gas in the atmosphere often can be explained by the presence of life. A separate sign of habitability, according to astrochemical will be the lack of carbon monoxide CO, serving as “an intermediate state” of carbon between its maximum and minimum oxidation state( +4 in carbon dioxide and -4 in methane).
The simultaneous presence of oxidized and reduced forms of carbon in the gas shell and the absence of CO is best explained by the existence of living organisms on the planet.