The orbit of the Venus Express spacecraft has a large eccentricity. Epigae is 68,000 km from the ground and Perigae is 250 km from the ground. This difference was used to measure the density of the atmosphere and its drag at the lowest altitude reached by the spacecraft
Research Methods
One of the goals of the Venus Express spacecraft is to measure the density of the atmosphere at the poles of the planet Venus. The usual way to do this is to make the measurements when the spacecraft passes over the atmosphere. In order to improve the measurements, it was decided to use new techniques that had not been performed until now. During its flight, it was decided to lower the release of the spacecraft so that it would pass through the atmosphere and then perform the necessary measurements. This extraordinary move was made in July August 2008, October 2009, February April 2010 (1).
Two techniques were used to perform these measurements. The first technique was used in 2008 and 2009. Atmospheric drag is used, which affects the spacecraft as a whole as it passes through the atmosphere. The atmosphere slows down the flight speed by causing a slight change in the flight path. Measuring this change makes it possible to measure the density of the atmosphere. The advantage of this method is that it makes it possible to measure point densities, while at a high altitude above the atmosphere the measured density is average (2).
In April 2010 a different technique was used. The spacecraft was lowered to a height of 180 km above the ground. During the measurements of the aerodynamic drag (airodrag), the solar collectors were rotated at different angles with the flight direction. This flight configuration exposed the solar collectors to the threshold point between the atmosphere and space. During this flight, a measurable aerodynamic torque is created. This winding is done several times. At the same time, the reaction wheels in the spaceship rotate in the opposite direction to the direction of flight in order to maintain the orientation of the spaceship during its flight. The solar collectors did not rotate symmetrically with each other. One collector sets perpendicular to the direction of flight and the other collector is rotated several times gradually in order to increase the twist and the balance is done by the reaction wheels. In the series of experiments she did on 16.4.2010, the two solar collectors were rotated at an angle of 0 45 with the direction of the flow of the atmosphere, in such a way that they mimic the blades of a wind farm. In this maneuver it is also possible to obtain information regarding the behavior of the molecules in the atmosphere. The entire spacecraft was used as a sensor for the purpose. The results of this experiment allowed planning another series of experiments of this kind in October 2010 and 2011 (1).
When the orbit of the spacecraft has a large eccentricity, Aphiga is at a distance of 68,000 km from the ground and Periga is at a distance of 250 km from the ground. At this stage, measuring the density of the atmosphere with these techniques is still not effective. For this purpose, in preparation for these measurements, the frigate was lowered to an altitude of 200 km and then the altitude of the track was reduced again to 180 km for several days. When the measurements are finished, the spacecraft is returned to the previous orbit (2).
The area of the wings is 5.7 square meters. It is possible that in future flights of spacecraft that will be launched to Venus, it will be possible to increase the area and the configuration of the solar collectors in order to improve these measurements and perhaps lower them to a lower altitude and measure the density of the atmosphere at different altitudes (the hypothesis of the author-Haim Mazar).
From the set of experiments that used these techniques, it turned out that the atmosphere above the poles is 60% thinner than they thought. This finding could indicate an unknown process operating in the atmosphere (2).
Atmospheric composition
Between the years 2006-2011, 59 measurements were made along the border line between the day side and the night side in the geographical area that extends from N 0 88 to S 0 77. A cold layer was discovered at an altitude of 125 km trapped between two warm layers located at heights of 100 km m and of 140 km. In several places the temperature drops to the freezing point of 2CO, which raises the possibility of the existence of ice or snow of 2CO (3). Due to the warm temperatures below the warm low layer, a strange phenomenon can occur. 2CO snow falls in the atmosphere of Venus, but it does not reach the ground. At the point where the temperature rises beyond its freezing point, the 2CO evaporates and a cycle of this gas is created, similar to the water cycle on Earth (the hypothesis of the writer-Haim Mezar).
At an altitude of 50-70 km there are clouds of 2 SO which, together with water vapor emitted from volcanoes, form drops of sulfuric acid (42 SO H). The 2SO should be broken down by the sun at an altitude of 70 km. In the observations made in 2008, a layer of sulfuric acid gas was found at an altitude of 90-100 km. The source of the gas is unknown. According to a computer model, sulfuric acid gas droplets probably evaporate at high altitudes and release sulfuric acid gas. At this height the sunlight releases the 2SO gas. This means that the cycle of sulfur in the atmosphere is more complex than thought (4).
Most likely, in the distant past, billions of years ago, there was more water vapor in the atmosphere than today. The loss of water vapor was caused by the ultraviolet radiation that broke the water molecules into oxygen atoms and hydrogen atoms and these escaped into space. The escape rate of hydrogen is 2 times greater than that of oxygen. It turned out that the heavy hydrogen (deuterium) enriches the upper atmosphere. Its atomic weight is greater than that of normal hydrogen, slowing down the rate of gas escape (5).
What is found today is the remains of the large amounts of water in the past. If all the water vapor found in the atmosphere today would condense to liquid water on the ground, its height would be only a few centimeters. There are differences between the amounts of water vapor at heights between 10 km and 100 km above the ground. A height of 100 km is above the clouds. The heavy water vapor cannot escape from the atmosphere as easily as normal water vapor (6). The amount of heavy water vapor in the upper atmosphere is probably twice as large as the amount of water vapor in the lower layers of the atmosphere (2).
In ultraviolet measurements made from an altitude of 38,000 km, bright areas and dark areas are visible and the difference between them is distinct. This difference is caused by the presence of an unknown substance in the clouds that absorbs the sun's ultraviolet radiation. It turned out that in the dark areas above the equator the temperature is relatively high. Convection currents lift up dark matter from below. In contrast to this, in the bright areas found above the middle latitudes, the temperature decreases as you go deeper towards the ground. The temperature reaches its minimum at the top of the clouds and prevents vertical mixing of the air. The cold air is ring-shaped and was named COLD COLLAR. It appears as a bright strip in the ultraviolet light (5).
From the observations of the Venus Express spacecraft, it turned out to the surprise of the researchers that Venus also has an ozone layer in the atmosphere, although it is thin. On Earth, the ozone layer is found in the stratosphere at heights between 15-5 km. The ozone on Earth is created as a result of the impact of the ultraviolet radiation that breaks down oxygen molecules and then the oxygen atoms connect with each other and create new oxygen molecules in the structure of 3O - ozone. This means that in any atmosphere that has oxygen there is the potential for ozone formation. Traces of ozone were discovered in the Martian atmosphere 40 years ago. The ozone layer on Venus is very thin and is found in varying ranges of height from the ground between 90-120 km and 5-10 km wide. The constant change of the ozone layer and its width indicate that there is some mechanism of unknown nature that keeps it at these altitudes. In the studies done before this discovery, it became clear that sunlight breaks down the CO 2 molecules and releases the oxygen (8). Helium and neon are also found in the atmosphere in small amounts and being noble gases they do not combine with other elements (9).
The spacecraft's passage through the atmosphere as mentioned earlier revealed another thing regarding the density of the atmosphere. There is a sharp difference in the density of the atmosphere between the day side and the night side (10). In Venus there is a process of atmosphere loss both on the day side and on the night side, although the loss is greater on the night side. Unlike the Earth, Venus does not have a magnetic field to protect the atmosphere from the solar wind. As a result, the solar wind hits the upper atmosphere and sprays particles from it into space. According to the researchers' assessment, it is this process that caused the loss of water for 4.5 billion years since the planet was formed. What is still not understood is the fact that the amount of hydrogen in the upper atmosphere is twice as large as expected. What causes this is unclear (2).
Clouds and eddies
During the spacecraft's observations, an atmospheric vortex "double eye" with a diameter of 2000 km was discovered in the South Pole, similar to a similar vortex that was discovered earlier in the North Pole. It has been known for several years that there is an atmospheric vortex at the South Pole, but recent observations have shown that it is much more complex than they thought. The vortex's shape and structure change in time frames of less than 24 hours. Compared to Earth, the South Pole vortex is more dynamic than terrestrial hurricanes. Although the general structure of the vortex can be in the shape of an "S" or the figure "8" in many cases it is chaotic. The origin of the variations in the velocities of the vortex formation is that the center of the vortex does not correspond to the geographic pole. The speed of the winds in the east-west direction depends on their location in the latitudes. The observations show that the vortex is contracted and stretched by shear waves. Although the main wind band moves in the opposite direction to the rotation of Venus around itself the speed. It is uniform as you approach the equator from latitude S 0 84.
The speed is less when moving towards the pole. The direction of movement reverses to the west-east direction near the latitude S 0 87. A wind with a smaller speed was detected at latitude S 0 75 and corresponds to the edge of the band of clouds which itself corresponds to a region of cold air surrounding the center of the vortex.
The location of the vortex center moves around the pole and it changes in cycles of 5-10 Earth days. Its average displacement from the South Pole is 0 3 of latitude - hundreds of kilometers. There is no correlation between the geographic location of the changing vortex centers (centroids) and the local time zones (local solar time). The general impression is that the vortex at the North Pole has a structure similar to that of the South Pole, but further observations are needed to confirm this assumption (11).
Temperatures
On Earth there is a phenomenon called "Hadley cells". This phenomenon occurs when warm air rises above the equator and moves towards the poles, places where it cools and sinks. Since the air near the ground is denser, it is compressed and heats the upper atmosphere above the poles. In the atmosphere of Venus the process is reversed. In addition to this, the heat changes are of the order of magnitude of C 0 30 in ranges of terrestrial days in the mesosphere and the thermosphere - above the low latitudes the metasphere is more stable. The range of heat changes is C 0 15. The mesosphere, and the thermosphere of Venus are very dynamic. Winds originating from heating by the sun and winds whose direction is east-west "compete" with each other and probably cause heat to be transferred to each other. The atmospheric changes (atmospheric variability) can have several reasons. Storms caused by air currents at different heights moving at speeds of more than 320 km/h and in opposite directions can transfer heat from below and the cold air moves up. All of these can cause changes in the upper atmosphere. In addition to this, the huge vortices active at the poles can themselves create storms and change the atmospheric pressure and consequently cause changes in heat.
The layers of the atmosphere above the clouds that were observed by the researchers are affected by changes in the intensity of the light coming from the sun in the transition zones between day and night or with progress in the latitudes towards the poles. At the high altitude where these layers are found, they can also be affected by solar activity such as solar explosions called flares and explosions of material from the sun known as coronal mass ejections in time spans of days, weeks and even a decade. The temperatures measured in 1990-1994 were higher than those measured in 2009. In a comparison between measurements made in 2007 and 2009, it was noticed that the temperatures from 2007 are higher in the equatorial region. From this set of data, additional observations are required to check how these phenomena affect the upper atmosphere in different time intervals (12).
Careful
In infrared observations, the Venus Express noticed the glow of the atmosphere on the night side of Venus. The source of the warning is the introduction of ultraviolet light into the atmosphere which breaks down nitric acid molecules into simpler atoms and molecules. The free atoms can recombine and in some cases the new molecules combine with energy which is then lost into space. On the day side some of the atoms connect back together and can be seen in visible light.
A nocturnal glow of nitric acid has not been observed so far either in the Earth's atmosphere or in that of Mars, despite the fact that their existence was known from ultraviolet observations. The Venus Express can watch 3 cautions at the same time. The nocturnal warning of molecules does not have to be at the same time. Understanding the process will become clearer when more observations are made (13).
Sources
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http://www.spacedaily.com/reports/Surfing_An_Alien_Atmosphere_999.html
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