For 10 years, scientists have been observing the state of the Venus atmosphere using sensors installed on spacecraft. As a result, it became clear that an important cause of cyclical climate change is the long-term fluctuations of the planet's albedo (reflectivity), which in turn is related to the number of mysterious dark spots in the atmosphere of Venus. These spots absorb solar radiation much more effectively than the surrounding lighter clouds, but their nature is not yet clear.
According to one version, they are clusters of microorganisms similar to those found in the Earth's atmosphere, although most likely more prosaic and the reason for the formation of zones with reduced reflectivity is associated with chemical reactions occurring in the atmosphere of Venus.
The human eye even in a telescope is not visible to a surface of the Venus as this planet is completely enveloped by a dense cover of the opaque clouds possessing high reflectivity. Unlike the Earth, where most of the solar energy is absorbed at the surface level, on Venus, this energy is mainly delayed in the clouds, and the climate on the planet largely depends on the reflectivity - albedo - of these clouds.
In general, the clouds of the upper layers of the carbon dioxide atmosphere of Venus, consisting mainly of sulfur dioxide and particles of sulfuric acid, rather poorly absorb solar radiation, reflecting up to 75% of the incident flow. However, against their background, dark spots are observed, within which absorption is up to 50% or more. These spots appear and disappear over time, changing their location and clarity of shape.
For the first time, dark spots in the atmosphere of Venus have been found out by ground telescopes more than a century ago. In fact, these are clusters of tiny particles of unknown nature (as they are called - unknown absorbers), formed near the upper level of the clouds and characterized by a wide range of absorption spectrum of solar energy - from ultraviolet to visible, reaching a maximum level in the region of 340-380 nm.
Various hypotheses have been proposed to explain the nature of dark spots at different times, ranging from purely chemical hypotheses (the formation of clusters of iron chloride, sulfur allotropes, sulfur dioxide, etc., as a result of atmospheric reactions in the upper atmosphere) to biogenic hypotheses (particles are approximately the same size and have the same light-absorbing properties as the microorganisms found in the Earth's atmosphere).
The hypothesis that the dark spots in the clouds of Venus are composed of microorganisms, at one time supported by such prominent scientists as the American biophysicist Harold J. Morowitz (Harold J. Morowitz) and the famous astronomer and astrophysicist Carl Sagan. On the surface of Venus, the living conditions are extreme (temperature around 450°C, pressure over 90 bar), but at the altitudes of 50-65 km the conditions are quite acceptable and resemble the terrestrial ones, so the biogenic hypothesis can not be simply taken and removed.
Neither observations nor results of modeling have yet been able to confirm the legitimacy of this or that hypothesis, because none of the types of microorganisms or inorganic substances do not fully correspond to the particles of Venus's dark spots in their spectral characteristics. Apparently, only the appearance of more advanced equipment and new research missions, within the framework of which the samples of the Venus atmosphere will be taken, will be able to put an end to this issue.
Between 2006 and 2014, Venus's albedo in the ultraviolet range steadily declined, resulting in a decline of almost half. The albedo then began to increase and reached the level of 2008-2009 between 2016 and 2017.
The modeling conducted by the authors of the study allowed us to reconstruct in more detail the picture of cyclic changes occurring in the atmosphere. The main elements of the atmospheric circulation of Venus are the zonal winds transporting heat between the day and night sides of the planet and the meridional winds determined by the movement of air masses of different temperature between low and high latitudes.
A serious fall of the albedo in 2006-2014 and, as a result, an increase in the amount of solar energy absorbed by the atmosphere (by 25-40% at high latitudes) has led to heating of the atmosphere and growth of the meridional temperature gradient between the poles and the equator. As a result, the average speed of zonal winds increased from 80-90 to 110 m/s. To a lesser extent, but the speed of meridional winds also increased.
Similarly, the increase of albedo in the period 2014-2018 resulted in a decrease of solar heating of the atmosphere and deceleration of the zonal wind speeds up to 100 m/s, as well as in the decrease of the meridional temperature gradient and decrease of the meridional wind speed. Thus, for the first time, the mechanism of albedo influence on long-term climatic changes was revealed.