The composition of the atmosphere is one of the most important characteristics of any planet. This is one of the factors directly affecting the formation of surface conditions. Chemistry of the atmosphere can tell scientists a lot about the processes of interaction of the gas shell of the planet with its bowels, on the one hand, and with phenomena of cosmic origin, on the other. A striking example of this is the composition of the atmosphere of the planet Venus.
Brief description of the atmosphere of the Morning Star
An extremely dense gas shell, a source of irreversible greenhouse effect, is, along with an impenetrable cloud layer, the main distinguishing feature of Venus.
Structurally, the atmosphere consists of several layers that differ in composition and physical properties. The lower, most dense layer is the troposphere, which extends to heights of about 65 km. Above, up to 120 km, there is a rarefied mesosphere, above it - the thermosphere and exosphere. In general, the gas shell of Venus is characterized by a much higher density than on Earth in the lower layers (surface pressure exceeds 93 atmospheres) and a lower density in the upper layers.
Clouds are located at altitudes of 50-65 km. At this level, the atmosphere has the property of superrotation: thanks to the strongest winds, it makes a complete revolution around the planet in four Earth days - much faster than Venus rotates.
Chemistry of the gas shell
The main component in the Venusian atmosphere is carbon dioxide. Significantly less nitrogen is contained, and negligible impurities are other gases.
Percentage of the atmosphere of Venus is expressed as follows:
- carbon dioxide CO 2 - about 96.5%;
- nitrogen N 2 - about 3.5%;
- sulfur dioxide SO 2 - 0.015%;
- argon Ar - 0.007%;
- water H 2 O - 0.002%;
- carbon monoxide CO - 0.0017%.
Helium, neon, oxygen, hydrogen, hydrogen halides HCl and HF, hydrogen sulfide are present in trace amounts. The total fraction of impurity gases in the chemical composition of the atmosphere of Venus does not exceed several hundredths of a percent.
Carbon dioxide sets the tone
How much carbon dioxide is in the Venusian air can be imagined by estimating the amount of nitrogen on Venus and on Earth. We remember that in the Earth’s atmosphere, nitrogen is more than three quarters - there is a lot of it. Even more nitrogen on Venus: its mass is approximately three times the mass of the entire Earth’s atmosphere. And while the percentage of nitrogen on Venus is 27.5 times lower than the proportion of carbon dioxide!
Carbon dioxide is a heavy gas, and it is concentrated in the lower atmosphere, causing the famous Venusian greenhouse effect, due to which the surface temperature is kept near 470 ° C. Due to its high density, carbon dioxide is in a state intermediate between gas and liquid.
Its presence in the atmosphere of Venus in such a large amount needs to be explained. It is estimated that the planet survived a global geological catastrophe about half a billion years ago, as a result of which the crust was completely destroyed. The widespread emergence of a huge amount of magma on the surface and its degassing could, as scientists believe, lead to such a massive jump in the content of carbon dioxide in the atmosphere.
Small but important impurity
The amount of sulfur dioxide in the atmosphere may seem insignificant. Venus, however, owes him one of its most remarkable features - the cloud layer. In the upper atmosphere, this gas, along with carbon dioxide and water vapor, is involved in the formation of sulfuric acid under the influence of hard solar ultraviolet radiation.
Droplets of acid “sink” in a dense Venusian atmosphere only to a certain level, below which the acid simply evaporates. Together with sulfur dioxide, these droplets form a layer of clouds that reflect most of the sunlight and make it impossible to observe the planet's surface in the optical range. It is thanks to them that Venus is such a bright object of the earth's sky.
It is assumed that intense volcanic activity was also a source of sulfur dioxide.
Dry planet
A widely known fact is that there is very little water on Venus. Of course, due to the greater proximity to the Sun, the protoplanetary substance from which the planet was formed should have contained fewer volatile components compared with the substance that formed the Earth. Still, there is too little water in Venus’s atmosphere. We are only talking about the atmosphere, since it is clear that under the conditions prevailing on the planet, no hydrosphere is possible, and all free water can exist exclusively in a vaporous state.
Planetologists believe that the tectonic catastrophe (mentioned above) that Venus survived led to the emission along with carbon dioxide and other gases of a large amount of water vapor - it is also a volcanic product. He, being the strongest greenhouse factor, could contribute to the establishment of the modern temperature regime of the atmosphere.
Being much lighter than carbon dioxide, water vapor concentrates at high altitudes. Here, the harsh ultraviolet radiation of the Sun enters into action, breaking up water molecules into oxygen, which is involved in the formation of sulfuric acid, and hydrogen. And since Venus does not have a global magnetic shield like the Earth’s shield, the ions of light gases - hydrogen, partially oxygen and some others - are easily lost by the atmosphere.
It is difficult to estimate how much water the planet could have lost in this way. Be that as it may, the question of the amazing “dryness” of Venus is still waiting for a final answer, and this answer is unlikely to be simple.
New discoveries ahead
A few years ago, due to the data of the European probe “Venus Express”, a weak ozone layer of the Venusian atmosphere was discovered at altitudes of about 100 km. It is formed again under the action of sunlight, which breaks down carbon dioxide molecules. Here, a temperature anomaly was recorded: the atmosphere at this altitude is several tens of degrees warmer. Scientists believe that the anomaly is associated with the release of energy in the decomposition of ozone.
The Venus-Express probe completed its mission in 2015, but the planet’s Akatsuki apparatus is currently exploring the planet’s atmosphere, whose tasks include, among other things, measuring the concentration of gases that make up the atmosphere of Venus at different altitudes. The probe also found a lot of interesting things. So, until an atmospheric component has been identified that absorbs soft ultraviolet, for example, at a wavelength of 365 nm. There is a hypothesis that iron chloride, possibly present in the cloud layer, is responsible for such absorption.
A lot of discoveries can be brought by comparing the data of modern and past missions, such as the Soviet "Venus" or "Vega-2." Thus, the study of the results of measuring the concentration of carbon dioxide and nitrogen obtained by descent vehicles allows us to more accurately imagine the processes in the poorly studied lower layers of the Venus gas shell. The composition of the atmosphere here and above is intricately related to its dynamics.
There are many discoveries and hypotheses in this area. Of course, new missions, for example, Venus-D, planned for the second half of the 2020s, will bring scientists a lot of information about the atmosphere of our neighbor, so similar and unlike Earth. Let's hope that these projects will be realized and become successful.