Mercury is the planet closest to the Sun. It belongs to the cosmic bodies of the earth group and is located relatively close to us. However, relatively little is known about Mercury today. Some time ago, he was considered the most poorly studied planet. Various parameters (surface character, climate features, the presence of the atmosphere, its composition) of Mercury remained a mystery due to the extremely inconvenient position of the planet for observation and research using spacecraft. The reason for this is the proximity to the Sun, which spoils any equipment directed in its direction or approaching it. Nevertheless, over the centuries of constant attempts at observation, impressive material has been collected, which, after the beginning of the space age, was supplemented by data from interplanetary stations. The atmosphere of Mercury is included in the list of characteristics that Mariner-10 and Messenger studied. The thin air shell of the planet, like everything on it, is subject to the constant influence of the luminary. The sun is the main factor that determines and shapes the characteristics of the atmosphere of Mercury.
Earth observation
Admiring Mercury from the surface of our planet is inconvenient because of its proximity to the Sun and the characteristics of the orbit. He appears in the sky close enough to the horizon. And always during sunset or dawn. The observation time is negligible. In the most favorable circumstances, it is about two hours before sunrise and the same after sunset. In most cases, the duration of observation does not exceed 20-30 minutes.
Phases
Mercury has the same phases as the moon. Flying around the Sun, it turns into a narrow sickle, then becomes a complete circle. In all its glory, the planet is visible when it is opposite the Earth, behind the Sun. At this time for the observer comes the "full moon" of Mercury. At the same time, however, the planet is at the maximum distance from the Earth, and bright sunlight interferes with observation.
Moving around the star, Mercury begins to visually increase in size, as it approaches us. At the same time, the area of the illuminated surface is reduced. In the end, the planet turns to us with its dark side and disappears from sight. Once every few years at such a moment, Mercury passes exactly between the Sun and the Earth. Then you can observe its movement on the disk of the star.
Observation Methods
Mercury can be seen with the naked eye or observed through binoculars shortly before dawn and after sunset, that is, at dusk. With the help of a small amateur telescope, it will be possible to notice the planet in the afternoon, but you will not be able to see any details. It is important during such observations - do not forget about safety. Mercury is never significantly removed from the Sun, which means that both eyes and equipment must be protected from its rays.
The ideal place to observe the planet closest to the luminary is mountain observatories and low latitudes. Here the astronomer comes to the aid of clean air, a cloudless sky, a short duration of twilight.
It was earthly observations that helped establish the fact that Mercury has no atmosphere. Powerful telescopes made it possible to consider many features of the surface relief of the planet and calculate the approximate temperature difference on the illuminated and dark sides. However, only flights of AMS (automatic interplanetary stations) were able to shed light on other characteristics of the planet and clarify the data already obtained.
Mariner 10
In the entire history of astronautics, only two spacecraft were sent to Mercury. The reason is a complex and expensive maneuver, which is necessary for the station to enter the planet’s orbit. The first to go to Mercury was Mariner 10. In 1974-1975, he flew three times around the planet closest to the Sun. The minimum distance that separated the apparatus and Mercury was 320 km. Mariner-10 transmitted several thousand images of the planet’s surface to Earth. About 45% of Mercury was captured. “Mariner-10” measured the surface temperature on the illuminated and dark side, as well as the magnetic field of the planet. In addition, the apparatus found that the atmosphere of Mercury is practically absent, it is replaced by a thin air shell, in which helium is present.
Messenger
The second AMC sent to Mercury was the Messenger. It started in August 2004. He transmitted to Earth an image of that part of the surface that was not captured by Mariner-10, measured the terrain of the planet, looked into its craters and discovered stains of obscure dark matter (possibly marks from meteorite impacts), which are often found here. The device studied solar flares, the magnetosphere of Mercury, its gas shell.
The messenger completed its mission in 2015. He fell on Mercury, leaving a crater 15 meters deep on the surface.
Is there an atmosphere on Mercury?
If you carefully reread the previous text, you will notice a slight contradiction. On the one hand, ground-based observations indicated the absence of any kind of gas shell. On the other hand, the Mariner-10 device transmitted information to the Earth, according to which the atmosphere of the planet Mercury still exists and contains helium. In the scientific community, this message was also surprising. And the point is not that it contradicted previous observations. Just Mercury does not have characteristics that contribute to the formation of a gas shell.
What is the atmosphere? This is a mixture of gases, volatile substances, which can only be held at the surface by gravity of a certain magnitude. Small by space standards, Mercury cannot boast of such a characteristic. The force of gravity on its surface is three times less than on Earth. Thus, the planet is not able to retain not only helium and hydrogen, but also heavier gases. Nevertheless, it was precisely helium that was discovered by Mariner-10.
Temperature
There is another factor that casts doubt on the presence of the atmosphere of Mercury. This is the surface temperature of the planet. Mercury is a record holder in this regard. In daylight, the surface temperature sometimes reaches 420-450 º. At such high values, the molecules and atoms of the gas begin to move faster and gradually reach a second cosmic velocity, that is, nothing can hold them at the surface. Under the temperature conditions of Mercury, the same helium should be the first to “escape”. In theory, it should not be on the planet closest to the Sun at all, and almost from the moment of its formation.
Special provision
Nevertheless, the answer to the question of whether there is an atmosphere on Mercury is positive, although it is somewhat different from what is usually hidden behind this astronomical concept. The reason for such a fantastic and at the same time quite real state of things lies in the unique location of the planet. The proximity of the luminary determines many characteristics of this cosmic body, and the atmosphere of Mercury is no exception.
The gas shell of the planet is constantly exposed to the so-called solar wind. It originates in the corona of the star and is a stream of nuclei, protons and electrons of helium. With the solar wind, fresh portions of volatile matter are delivered to Mercury. Without such a feed, all helium would disappear from the surface of the planet in about two hundred days.
Atmosphere of Mercury: composition
Careful research has helped to find other elements that make up the gas shell of the planet. The atmosphere of Mercury also contains hydrogen, oxygen, potassium, calcium and sodium. The percentage of these elements is very small. In addition, the atmosphere of the planet Mercury is characterized by the presence of traces of carbon dioxide.
The air shell is very thin. The gas molecules in it do not actually interact with each other, but only move along the surface without collisions and collisions. Scientists have been able to establish the factors that determine the presence of the atmosphere of Mercury. Hydrogen, like helium, is supplied to its surface by the solar wind. The source of other elements is the planet itself or meteorites falling on it. The atmosphere of Mercury, the composition of which is planned to be thoroughly studied in the near future, is presumably formed as a result of the evaporation of rocks under the influence of the solar wind or diffusion from the bowels of the planet. Most likely, each of these factors contributes.
So what is the atmosphere of Mercury? Highly rarefied, consisting of helium, hydrogen, traces of alkali metals and carbon dioxide. Often in the scientific literature it is called the exosphere, which only emphasizes the strong difference between this shell and a similar formation, for example, on Earth.
Despite all the difficulties, the planet Mercury still appears on the list of space research goals. The atmosphere and surface of this cosmic body are likely to be studied more than once with the help of various devices. Mercury is still fraught with a lot of interesting and unknown. In addition, the study of such planets as Venus, Mars or Mercury, whether they are deprived of the atmosphere or not, sheds light on the history of the formation and development of the Earth.