Mercury is the smallest planet in the world, is located at the closest distance from the Sun, and belongs to the terrestrial planets. The mass of Mercury is approximately 20 times less than that of Earth; the planet has no natural satellites. According to scientists, the planet has a frozen iron core, occupying about half the volume of the planet, followed by a mantle, and a silicate shell on the surface.
The surface of Mercury is very similar to the Moon, and is densely covered with craters, most of which are of impact origin - from collisions with fragments that remained from the time of formation solar system about 4 billion years because. The planet's surface is covered with long, deep cracks, which may have formed as a result of the gradual cooling and compression of the planet's core.
The similarity between Mercury and the Moon lies not only in the landscape, but also in a number of other features, in particular the diameter of both celestial bodies - 3476 km for the Moon, 4878 for Mercury. A day on Mercury is equal to approximately 58 Earth days, or exactly 2/3 of a Mercury year. Connected with this is another curious fact of “lunar” similarity - from the Earth, Mercury, like the Moon, is always visible only the “front side”.
The same effect would occur if a Mercurian day were exactly equal to a Mercurian year, so before space age and observations using radar, it was believed that the period of rotation of the planet around its axis was 58 days.
Mercury moves very slowly around its axis, but moves very quickly in its orbit. On Mercury, a solar day is equal to 176 earthly days, that is, during this time, thanks to the addition of the orbital and axial movements, two “Mercurian” years have time to pass on the planet!
Atmosphere and temperature on Mercury
Thanks to spacecraft, it was possible to find out that Mercury has an extremely rarefied helium atmosphere, which contains an insignificant state of neon, argon and hydrogen.
As for the properties of Mercury itself, they are in many ways similar to the lunar ones - on the night side the temperature drops to -180 degrees Celsius, which is enough to freeze carbon dioxide and liquefy oxygen, on the day side it rises to 430, which is enough to melt lead and zinc . However, due to the extremely weak thermal conductivity of the loose surface layer, already at a depth of a meter the temperature stabilizes at plus 75.
This is due to the lack of a noticeable atmosphere on the planet. However, there is still some semblance of an atmosphere - from atoms emitted as part of the solar wind, mostly metallic.
Study and observation of Mercury
It is possible to observe Mercury, even without the help of a telescope, after sunset and before sunrise, however, certain difficulties arise due to the location of the planet; even during these periods it is not always noticeable.
When projected onto the celestial sphere, the planet is visible as a star-shaped object that does not move further than 28 degrees of arc from the Sun, with a greatly varying brightness - from minus 1.9 to plus 5.5 magnitude, that is, approximately 912 times. You can notice such an object at dusk only in ideal atmospheric conditions and if you know where to look. And the displacement of the “star” per day exceeds four degrees of arc - it was for this “speed” that the planet at one time received its name in honor of the Roman god of trade with winged sandals.
Near perihelion, Mercury comes so close to the Sun and its orbital speed increases so much that to an observer on Mercury the Sun appears to be moving backwards. Mercury is so close to the Sun that it is very difficult to observe.
In mid-latitudes (including Russia), the planet is visible only in the summer months and after sunset.
You can observe Mercury in the sky, but you need to know exactly where to look - the planet is visible very low above the horizon (lower left corner)
- The temperature on the surface of Mercury varies significantly: from –180 C on the dark side to +430 C on the sunny side. Moreover, since the planet’s axis almost never deviates from 0 degrees, even on the planet closest to the Sun (at its poles), there are craters whose bottoms have never been reached by the sun’s rays.
2. Mercury makes one revolution around the Sun in 88 Earth days, and one revolution around its axis in 58.65 days, which is 2/3 of one year on Mercury. This paradox is caused by the fact that Mercury is affected by the tidal influence of the Sun.
3. Mercury has tension magnetic field 300 times less than the magnetic field strength of planet Earth, the magnetic axis of Mercury is inclined to the axis of rotation by 12 degrees.
4. Mercury is the smallest of all the terrestrial planets; it is so small that it is inferior in size to the largest satellites of Saturn and Jupiter - Titan and Ganymede.
5. Despite the fact that the closest orbits to the Earth are Venus and Mars, Mercury has been closer to the Earth for a longer period of time than any other planet.
6. The surface of Mercury resembles the surface of the Moon - it, like the Moon, is dotted with a large number of craters. The biggest and most important difference between these two bodies is the presence on Mercury large number jagged slopes - the so-called scarps, which extend for several hundred kilometers. They were formed by compression, which accompanied the cooling of the planet's core.
7. Perhaps the most noticeable detail on the surface of the planet is the Plain of Heat. This is a crater that got its name due to its location near one of the “hot longitudes”. 1300 km is the diameter of this crater. The body that hit the surface of Mercury in time immemorial must have had a diameter of at least 100 km.
8. The planet Mercury rotates around the Sun at an average speed of 47.87 km/s, making it the fastest planet in the Solar System.
9. Mercury is the only planet in the solar system that has Joshua effect. This effect looks like this: The Sun, if we observed it from the surface of Mercury, at a certain moment would have to stop in the sky, and then continue moving, but not from east to west, but on the contrary - from west to east. This is possible due to the fact that within approximately 8 days the speed rotational movement Mercury is less than the planet's orbital speed.
10. Not so long ago, thanks to mathematical modeling, scientists came up with the idea that Mercury is not an independent planet, but a long-lost satellite of Venus. However, while there is no physical evidence, this is nothing more than a theory.
Mercury is the smallest and closest planet to the Sun in the Solar System. The ancient Romans gave it its name in honor of the god of trade Mercury, the messenger of other gods who wore winged sandals, because the planet moves faster than others in the sky.
a brief description of
Due to its small size and proximity to the Sun, Mercury is inconvenient for earthly observations, therefore for a long time very little was known about him. An important step in its study was made thanks to the Mariner-10 and Messenger spacecraft, with the help of which high-quality images were obtained and detailed map surfaces.
Mercury is a terrestrial planet and is located at an average distance of about 58 million km from the Sun. In this case, the maximum distance (at aphelion) is 70 million km, and the minimum (at perihelion) is 46 million km. Its radius is only slightly larger than that of the Moon - 2,439 km, and its density is almost the same as that of the Earth - 5.42 g/cm³. High density means that it contains a significant proportion of metals. The mass of the planet is 3.3 10 23 kg, and about 80% of it is the core. Acceleration free fall 2.6 times less than on Earth - 3.7 m/s². It is worth noting that the shape of Mercury is ideally spherical - it has zero polar compression, that is, its equatorial and polar radii are equal. Mercury has no satellites.
The planet orbits the Sun in 88 days, and the period of rotation around its axis relative to the stars (sidereal day) is two-thirds of the orbital period - 58 days. This means that one day on Mercury lasts two of its years, that is, 176 Earth days. The commensurability of the periods is apparently explained by the tidal influence of the Sun, which slowed down the rotation of Mercury, which was initially faster, until their values became equal.
Mercury has the most elongated orbit (its eccentricity is 0.205). It is significantly inclined to the plane of the earth's orbit (the ecliptic plane) - the angle between them is 7 degrees. The planet's orbital speed is 48 km/s.
The temperature on Mercury was determined by its infrared radiation. It varies over a wide range from 100 K (-173 °C) at night and the poles to 700 K (430 °C) at noon at the equator. At the same time, daily temperature fluctuations quickly decrease as one moves deeper into the crust, that is, the thermal inertia of the soil is high. From this it was concluded that the soil on the surface of Mercury is the so-called regolith - highly fragmented rock with low density. The surface layers of the Moon, Mars and its satellites Phobos and Deimos also consist of regolith.
Education of the planet
The most likely description of the origin of Mercury is considered to be the nebular hypothesis, according to which the planet was in the past a satellite of Venus, and then for some reason came out of the influence of its gravitational field. According to another version, Mercury was formed simultaneously with all objects of the Solar system in the inner part of the protoplanetary disk, from where light elements were already carried by the solar wind to the outer regions.
According to one version of the origin of Mercury's very heavy inner core - the giant impact theory - the planet's mass was initially 2.25 times greater than its current one. However, after a collision with a small protoplanet or planet-like object, most of the crust and upper mantle was scattered into space, and the core began to make up a significant portion of the planet's mass. The same hypothesis is used to explain the origin of the Moon.
After the completion of the main stage of formation 4.6 billion years ago, Mercury was intensively bombarded by comets and asteroids for a long time, which is why its surface is dotted with many craters. Violent volcanic activity at the dawn of Mercury's history led to the formation of lava plains and "seas" inside the craters. As the planet gradually cooled and contracted, other relief features were born: ridges, mountains, hills and ledges.
Internal structure 
The structure of Mercury as a whole differs little from the other terrestrial planets: in the center there is a massive metallic core with a radius of about 1800 km, surrounded by a layer of mantle of 500 - 600 km, which, in turn, is covered with a crust 100 - 300 km thick.
It was previously believed that Mercury's core is solid and makes up about 60% of its total mass. It was assumed that such a small planet could only have a solid core. But the presence of the planet’s own magnetic field, albeit weak, is a strong argument in favor of the version of its liquid core. The movement of matter inside the core causes a dynamo effect, and the strong elongation of the orbit causes a tidal effect that maintains the core in a liquid state. It is now reliably known that the core of Mercury consists of liquid iron and nickel and accounts for three-quarters of the mass of the planet.
The surface of Mercury is practically no different from the moon. The most noticeable similarity is the countless number of craters, large and small. As on the Moon, young craters radiate in different sides light rays. However, Mercury does not have such vast seas, which would also be relatively flat and free of craters. Another noticeable difference in the landscapes is the numerous ledges hundreds of kilometers long, formed by the compression of Mercury.
Craters are located unevenly on the surface of the planet. Scientists suggest that areas more densely filled with craters are older, and smoother areas are younger. Also, the presence of large craters suggests that there have been no crustal shifts or surface erosion on Mercury for at least 3-4 billion years. The latter is proof that the planet never had a sufficiently dense atmosphere.
The largest crater on Mercury is about 1,500 kilometers in size and 2 kilometers in height. Inside it there is a huge lava plain - the Plain of Heat. This object is the most noticeable feature on the planet's surface. The body that collided with the planet and gave birth to such a large-scale formation must have been at least 100 km long.
The probes' images showed that the surface of Mercury is homogeneous and the reliefs of the hemispheres do not differ from each other. This is another difference between the planet and the Moon, as well as from Mars. The composition of the surface is noticeably different from the lunar one - it contains few of the elements that are characteristic of the Moon - aluminum and calcium - but quite a lot of sulfur.
Atmosphere and magnetic field
The atmosphere on Mercury is practically absent - it is very rarefied. Its average density is equal to the same density on Earth at an altitude of 700 km. Its exact composition has not been determined. Thanks to spectroscopic studies, it is known that the atmosphere contains a lot of helium and sodium, as well as oxygen, argon, potassium and hydrogen. Atoms of elements are brought from outer space by the solar wind or raised from the surface by it. One source of helium and argon is radioactive decay in the planet's crust. The presence of water vapor is explained by the formation of water from hydrogen and oxygen contained in the atmosphere, impacts of comets on the surface, and sublimation of ice, presumably located in craters at the poles.
Mercury has a weak magnetic field, the strength of which at the equator is 100 times less than on Earth. However, such tension is enough to create a powerful magnetosphere for the planet. The field axis almost coincides with the rotation axis; the age is estimated at approximately 3.8 billion years. The interaction of the field with the solar wind enveloping it causes vortices that occur 10 times more often than in the Earth's magnetic field.
Observation
As already mentioned, observing Mercury from Earth is quite difficult. It is never more than 28 degrees away from the Sun and is therefore practically invisible. The visibility of Mercury depends on geographical latitude. It is easiest to observe it at the equator and latitudes close to it, since twilight lasts the shortest here. At higher latitudes, Mercury is much more difficult to see - it is very low above the horizon. Here best conditions for observation come during greatest removal Mercury from the Sun or on highest altitude above the horizon during sunrise or sunset. It is also convenient to observe Mercury during the equinoxes, when the duration of twilight is minimal.
Mercury is fairly easy to see with binoculars just after sunset. The phases of Mercury are clearly visible in a telescope of 80 mm in diameter. However, surface details, naturally, can only be seen in much more detail. large telescopes, and even with such tools it will be a difficult task.
Mercury has phases similar to the phases of the Moon. At a minimum distance from the Earth, it is visible as a thin crescent. IN full phase it is too close to the Sun to be seen.
When launching the Mariner 10 probe to Mercury (1974), a gravity assist maneuver was used. Direct flight of the device to the planet
required enormous amounts of energy and was practically impossible. This difficulty was circumvented by correcting the orbit: first, the device passed by Venus, and the conditions for flying past it were selected so that its gravitational field changed its trajectory just enough that the probe reached Mercury without additional expenditure of energy.
There are suggestions that ice exists on the surface of Mercury. Its atmosphere contains water vapor, which may well exist in a solid state at the poles inside deep craters.
In the 19th century, astronomers observing Mercury could not find an explanation for its orbital motion using Newton's laws. The parameters they calculated differed from the observed ones. To explain this, it was hypothesized that there is another invisible planet Vulcan in the orbit of Mercury, the influence of which introduces the observed inconsistencies. The real explanation came decades later using Einstein's general theory of relativity. Subsequently, the name of the planet Vulcan was given to vulcanoids - supposed asteroids located inside the orbit of Mercury. Zone from 0.08 AU up to 0.2 a.u. gravitationally stable, so the probability of the existence of such objects is quite high.
Mercury is similar in physical characteristics to the Moon. It has no natural satellites, its atmosphere is very rarefied. This planet has a large iron core, accounting for 83% of the volume of the entire planet. This core is the source of a magnetic field with a strength of 0.01 of the earth's. The surface temperature of the planet is - 90 - 700 K (-183.15-426.85 C). The solar side of the planet is heating up significantly more than its back side and polar regions.
Craters of Mercury
On the surface of Mercury there is a large number of craters, this landscape is very reminiscent of the lunar one. The density of craters differs in different parts of Mercury. It is possible that the areas of the planet's surface that are more heavily dotted with craters are more ancient, and those that are less dotted are younger. They were formed as a result of lava flooding the old surface. At the same time, there are fewer large craters on Mercury than on the Moon. The diameter of the largest crater on Mercury is 716 km, it was named after Rembrandt, the great Dutch painter. Also on Mercury there are formations that are not similar on the Moon. For example, scarps are numerous jagged slopes that extend for hundreds of kilometers. When studying the scarps, it was found that they were formed during the compression of the surface that accompanied the cooling of Mercury, during which the surface area of the planet decreased by 1%. Because There are well-preserved large craters on the surface of Mercury, which means that over the past 3 - 4 billion years there has been no movement of sections of the crust on a large scale, there was no erosion on the surface (by the way, the latter almost completely confirms the impossibility of the existence in the history of Mercury of any some significant atmosphere).
During the research, the Messenger probe obtained photographs of more than 80% of the planet's surface, as a result of which it was determined that it was homogeneous, unlike the surface of Mars or the Moon, in which one hemisphere is very different from the other.
The elemental composition of Mercury's surface, obtained by the Messenger X-ray fluorescence spectrometer, showed that the planet's surface is rich in plagioclase feldspar, characteristic of the continental regions of the Moon, and, in comparison, poor in calcium and aluminum. It is also rich in magnesium and low in iron and titanium, allowing it to fill the gap between ultrabasic rocks, like terrestrial komatiites, and typical basalts. A relative abundance of sulfur has also been discovered - this means that the planet was formed under reducing conditions.
The craters of Mercury differ from each other. They can be small bowl-shaped depressions, or multi-ring impact craters that are hundreds of kilometers in diameter. Mercury's craters to varying degrees destroyed. There are more or less well-preserved ones, with long rays located around them, formed during the release of substance from the impact of the impact. There are also very destroyed remains of craters.
The Plain of Heat (lat. Caloris Planitia) is one of the most noticeable features of the relief of Mercury. It is so named because it is located next to one of the “hot longitudes”. The diameter of this plain is about 1550 km.
Most likely, the body, the collision of which with the surface of Mercury formed a crater, was at least 100 km in diameter. The impact was so strong that seismic waves, having passed through the entire planet and gathered at the opposite point of the surface, caused the formation of a kind of “chaotic” rugged landscape on Mercury. The force of the impact is also evidenced by the fact that it provoked the emission of lava, as a result of which the Zhary Mountains, more than 2 km high, were formed around the crater. Kuiper Crater (60 km across) is the point on the planet's surface with the highest albedo. Most likely, Kuiper crater is one of the “last” large craters on Mercury to form.
Another interesting arrangement of craters on the planet was discovered by scientists in 2012: the sequence of crater locations forms the face of Mickey Mouse. Maybe in the future this configuration will be called that way.
Geology of Mercury
More recently, it was believed that in the depths of Mercury there is a metallic core, the radius of which 
Rogo 1800 - 1900 km, it makes up 60% of the mass of the planet, since a weak magnetic field was discovered by the Mariner 10 spacecraft. In addition, according to scientists, it was believed that the core of Mercury, due to the small size of the planet, should not be liquid. After five years of radar observations, Jean-Luc Margot's group took stock in 2007, and as a result, various variations in Mercury's rotation were noted, which are too large for a planet with a solid core. Based on this, we can say with almost one hundred percent accuracy that Mercury’s core is liquid.
Compared to any planet in the solar system, Mercury's core has a higher percentage of iron. There are several versions of the explanation for this. The most widely accepted theory in the world of science says that Mercury, while originally 2.25 times as massive as it is today, had the same proportion of silicates and metal as a normal meteorite. But at the very beginning of the history of the Solar System, a planet-like body, several hundred kilometers in diameter and with a mass 6 times less, collided with Mercury. Because of this collision, a large part of the primary crust and mantle was torn away from the planet, as a result of which the relative proportion of the core in the composition of Mercury increased. By the way, to explain the formation of the Moon, a similar hypothesis was proposed, called the Giant Impact Theory. But this theory is contradicted by the first data obtained during the study of the elemental composition of the surface of Mercury using the AMS Messenger gamma spectrometer (it allows measuring the content radioactive isotopes). It turned out that there is a lot of potassium on the planet (a volatile element when compared with thorium and uranium, which are more refractory). This is not consistent with the inevitable collision high temperatures. Based on this, it becomes clear that the elemental composition of Mercury coincides with the primary elemental composition of the material that formed it, which is close to anhydrous cometary particles and enstatite chondrites, while the iron content in the latter, to date, is small to explain the high average density of the planet.
A silicate mantle (500-600 km thick) surrounds Mercury's core. The thickness of its crust ranges from 100 to 300 km (according to Mariner-10 data).
Geological history of Mercury
The geological history of the planet is divided into eras, like those of Mars, the Moon and the Earth. These eras are called as follows (to the later from the earlier): 1- pre-Tolstovsky, 2- Tolstoyan, 3- Kalorian, 4- late Kalorian, 5- Mansurian and 6- Kuiper. And the relative geological age of Mercury is divided into periods according to these eras. True, the absolute age measured in years has not been precisely established.
About 4.6 billion years ago, when the planet was already formed, there was an intense collision with comets and asteroids. The last massive bombardment of Mercury was 3.8 billion years ago. Some areas (for example, the Plain of Heat) were created, among other things, by filling them with lava. As a result, smooth cavities similar to those of the Moon formed inside the craters.
After this, as Mercury cooled and contracted, faults and ridges formed. The later time of their formation is evidenced by their location on the surface of large relief objects, such as plains and craters. The planet's time of volcanism ended after the mantle shrank enough to prevent lava from reaching Mercury's surface. It is possible that this happened during the first 700-800 million years since the formation of Mercury. Later changes in the planet's landscape were caused by impacts of cosmic bodies on its surface.
Mercury's magnetic field
The strength of Mercury's magnetic field is approximately one hundred times less than that of Earth and is equal to ~300 nT. Mercury's magnetic field has a dipole structure, is very symmetrical, its axis is only 10 degrees deviated from Mercury's rotation axis. This significantly reduces the number of hypotheses explaining the origin of Mercury's magnetic field. Presumably, Mercury's magnetic field arises as a result of the dynamo effect (the same happens on Earth). Perhaps this effect is a consequence of the circulation of the liquid core. The very strong tidal effect occurs due to the very pronounced eccentricity of Mercury. This tidal effect keeps the core liquid, which is mandatory conditions to create a dynamo effect. The planet's magnetic field is so strong that it can change the direction of the solar wind around Mercury, resulting in the creation of its magnetosphere. And although it is so small that it would fit inside the Earth, it is powerful enough to catch the plasma of the solar wind. As a result of observations obtained with the help of Mariner 10, it turned out that there is low-energy plasma in the magnetosphere of the night side of Mercury. Explosions of active particles in the tail of the magnetosphere indicate its inherent dynamic qualities.
On October 6, 2008, Messenger, flying by Mercury for the second time, recorded a large number of windows in the planet’s magnetic field. Messenger discovered the phenomenon of magnetic vortices. These are intertwined magnetic field knots that connect the spacecraft to Mercury's magnetic field. The diameter of the vortex was 800 km, this is a third of the radius of the planet. The solar wind creates such a vortex form of the magnetic field. As the solar wind flows around Mercury's magnetic field, it binds and rushes with it, forming into vortex-like structures. Such vortices create windows in the planet’s magnetic shield; the solar wind penetrates through them, reaching the surface of the planet. The connection between interplanetary and planetary magnetic fields (magnetic reconnection) is a common cosmic phenomenon that also occurs near the Earth at a time when it creates magnetic vortices. But the frequency of Mercury’s magnetic reconnection, according to Messenger, is 10 times higher.
Photo taken from the MESSENGER spacecraft.
The planet Mercury is the closest planet to the Sun. It is located at a distance of only 58 million km from our star (for comparison, from Earth to the Sun is 150 million km). Like all planets, It is named after a Roman god, in this case, the Roman god of trade - just like ancient greek god Hermes.
Its diameter is only 4879 km, making it the smallest planet in the solar system. It is even smaller than the moons Ganymede and Titan. But it has a metallic core that makes up almost half the volume of the planet. This gives it greater mass and stronger gravity than one would expect. On Mercury, your weight would be 38% of your weight on Earth.
Orbit
Mercury revolves around the Sun in a highly elongated elliptical orbit.
At its closest point, it approaches the Sun at 46 million km, and then moves away to 70 million km. It takes the planet only 88 days to orbit the Sun.
At first glance, Mercury is quite similar to our Moon. It has a surface covered with craters, as well as ancient lava flows. The largest crater is the Caloris Basin, almost 1300 km across. Like our Moon, it has no discernible atmosphere. But below the surface is very different from the Moon. It has a huge core of iron surrounded by a thick layer of mantle rocks and a thin crust. gravity on the planet is 1/3 of Earth's.
It rotates slowly around its axis, completing one revolution every 59 days.
Atmosphere
It is very rarefied and consists of captured particles of the Solar wind. Without an atmosphere, it cannot retain heat from the Sun. The side that faces the Sun heats up to a temperature of 450 °C, while the shadow side cools to -170 °C.
Study
BepiColumbo, which was launched to explore the planet
The first spacecraft to reach Mercury was Mariner 10, which flew past the planet in 1974. He managed to photograph about half of the planet's surface over several flybys. Then in 2004 NASA launched the MESSENGER spacecraft mission. On this moment, the spacecraft has entered orbit and is studying it in great detail.
If you want to see it without a telescope, it is difficult to do because the planet is in the bright rays of the Sun most time.
When visible, you can see it in the west just after sunset, or in the east before sunrise. In a telescope, the planet has phases like the Moon, depending on its position in its orbit.
So, what is the planet Mercury and what is so special about it that makes it different from other planets? Probably, first of all, it’s worth listing the most obvious things that can be easily gleaned from different sources, but without which it will be difficult for a person to form an overall picture.
At the moment (after Pluto was “demoted” to dwarf planets) Mercury is the smallest of the eight planets in our solar system. Also, the planet is at the closest distance from the Sun, and therefore rotates around our star much faster than the other planets. Apparently, it was precisely the latter quality that served as the reason to name her in honor of the fastest-footed messenger of the Gods named Mercury, an extraordinary character from legends and myths Ancient Rome with phenomenal speed.
By the way, it was the ancient Greek and Roman astronomers who more than once called Mercury both the “morning” and “evening” star, although for the most part they knew that both names correspond to the same cosmic object. Even then, the ancient Greek scientist Heraclitus pointed out that Mercury and Venus rotate around the Sun, and not around.
Mercury today
Today, scientists know that due to Mercury's close proximity to the Sun, temperatures on its surface can reach up to 450 degrees Celsius. But the lack of an atmosphere on this planet does not allow Mercury to retain heat and on the shadow side the surface temperature can drop sharply to 170 degrees Celsius. The maximum temperature difference between daytime and nighttime on Mercury turned out to be the highest in the Solar System - more than 600 degrees Celsius.
Mercury is small in size bigger than the moon, but at the same time much heavier than our natural satellite.
Despite the fact that the planet has been known to people since time immemorial, the first image of Mercury was obtained only in 1974, when the Mariner 10 spacecraft transmitted the first images in which it was possible to make out some features of the relief. After this, a long-term active phase began to study this cosmic body, and several decades later, in March 2011, a spacecraft called Messenger reached the orbit of Mercury. after which, finally, humanity received answers to many questions.
The atmosphere of Mercury is so thin that it practically does not exist, and the volume is about 10 to the fifteenth power less than the dense layers of the Earth's atmosphere. Moreover, the vacuum in the atmosphere of this planet is much closer to true vacuum, if we compare it with any other vacuum created on Earth using technical means.
There are two explanations for the lack of atmosphere on Mercury. Firstly, this is the density of the planet. It is believed that with a density of only 38% of the Earth's density, Mercury is simply not able to retain much of the atmosphere. Secondly, the proximity of Mercury to the Sun. Such a close distance to our star makes the planet most susceptible to the influence of solar winds, which remove the last remnants of what can be called an atmosphere.
However, no matter how scarce the atmosphere on this planet is, it still exists. According to the space agency NASA, in its own way chemical composition it consists of 42% oxygen (O2), 29% sodium, 22% hydrogen (H2), 6% helium, 0.5% potassium. The remaining insignificant part consists of molecules of argon, carbon dioxide, water, nitrogen, xenon, krypton, neon, calcium (Ca, Ca +) and magnesium.
It is believed that the rarefaction of the atmosphere is due to the presence of extreme temperatures on the surface of the planet. The most low temperature can be on the order of -180 °C, and the highest is approximately 430 °C. As mentioned above, Mercury has the largest range of surface temperatures of any planet in the Solar System. The extreme maxima present on the side facing the Sun are precisely the result of an insufficient atmospheric layer that is not able to absorb solar radiation. By the way, the extreme cold on the shadow side of the planet is due to the same thing. The absence of a significant atmosphere does not allow the planet to retain solar radiation and heat very quickly leaves the surface, freely escaping into outer space.
Until 1974, the surface of Mercury remained largely a mystery. Observations of this cosmic body from Earth were very difficult due to the proximity of the planet to the Sun. It was possible to see Mercury only before dawn or immediately after sunset, but on Earth at this time the line of visibility is significantly limited by the too dense layers of our planet’s atmosphere.
But in 1974, after a magnificent three-time flyby of the surface of Mercury by the Mariner 10 spacecraft, the first fairly clear photographs of the surface were obtained. Surprisingly, despite significant time constraints, the Mariner 10 mission photographed almost half of the entire surface of the planet. As a result of analyzing observational data, scientists were able to identify three significant features of the surface of Mercury.
The first feature is the huge number of impact craters that gradually formed on the surface over billions of years. The so-called Caloris basin is the largest of the craters, with a diameter of 1,550 km.
The second feature is the presence of plains between the craters. These smooth surface areas are believed to have been created by the movement of lava flows across the planet in the past.
And finally, the third feature is the rocks, scattered across the entire surface and reaching from several tens to several thousand kilometers in length and from one hundred meters to two kilometers in height.
Scientists especially emphasize the contradiction of the first two features. The presence of lava fields indicates that there was once active volcanic activity in the planet's historical past. However, the number and age of craters, on the contrary, indicate that Mercury was geologically passive for a very long time.
But the third one is no less interesting. distinguishing feature surface of Mercury. It turned out that the hills are formed by the activity of the planet’s core, which results in the so-called “bulging” of the crust. Similar bulges on Earth are usually associated with the displacement of tectonic plates, while the loss of stability of Mercury's crust occurs due to the contraction of its core, which is gradually compressed. The processes occurring at the core of the planet lead to compression of the planet itself. Recent calculations by scientists indicate that the diameter of Mercury has decreased by more than 1.5 kilometers.
Structure of Mercury
Mercury is made up of three distinct layers: the crust, the mantle, and the core. The average thickness of the planet's crust, according to various estimates, ranges from 100 to 300 kilometers. The presence of the previously mentioned bulges on the surface, whose shape resembles those of the earth, indicates that, despite being sufficiently hard, the crust itself is very fragile.
The approximate thickness of Mercury's mantle is about 600 kilometers, which suggests that it is relatively thin. Scientists believe that it was not always so thin and that in the past there was a collision of the planet with a huge planetesmial, which led to the loss of significant mass of the mantle.
The core of Mercury has become the subject of much research. It is believed to be 3,600 kilometers in diameter and has some unique properties. The most interesting property is its density. Considering that the planetary diameter of Mercury is 4878 kilometers (it is smaller than the satellite Titan, whose diameter is 5125 kilometers, and the satellite Ganymede with a diameter of 5270 kilometers), the density of the planet itself is 5540 kg/m3 with a mass of 3.3 x 1023 kilograms.
So far, there is only one theory that has attempted to explain this feature of the planet's core, and has cast doubt on whether Mercury's core is actually solid. Having measured the characteristics of the bounce of radio waves from the surface of the planet, a group of planetary scientists came to the conclusion that the planet’s core is actually liquid and this explains a lot.
Mercury's orbit and rotation
Mercury is much closer to the Sun than any other planet in our system and, accordingly, it requires the shortest time to orbit. A year on Mercury is only about 88 Earth days.
An important feature of Mercury's orbit is its high eccentricity compared to other planets. Additionally, of all the planetary orbits, Mercury's orbit is the least circular.
This eccentricity, along with the lack of a significant atmosphere, explains why Mercury's surface experiences the widest range of temperature extremes in the Solar System. Simply put, Mercury's surface heats up much more when the planet is at perihelion than at aphelion, because the difference in distance between these points is too great.
The orbit of Mercury itself is an excellent example of one of the leading processes of modern physics. We are talking about a process called precession, which explains the shift in Mercury's orbit relative to the Sun over time.
Despite the fact that Newtonian mechanics (i.e. classical physics) predicts the rates of this precession in great detail, the exact values have never been determined. This became a real problem for astronomers in the late nineteenth and early twentieth centuries. Many concepts have been formulated to explain the differences between theoretical interpretations and actual observations. According to one theory, it was even suggested that there is an unknown planet whose orbit is closer to the Sun than that of Mercury.
However, the most plausible explanation was found after it was published general theory Einstein's relativity. Based on this theory, scientists were finally able to describe the orbital precession of Mercury with sufficient accuracy.
Thus, for a long time it was believed that Mercury's spin-orbit resonance (the number of revolutions in its orbit) was 1:1, but it was eventually proven that it was actually 3:2. It is thanks to this resonance that a phenomenon is possible on the planet that is impossible on Earth. If an observer were on Mercury, he would be able to see that the Sun rises to the highest point in the sky, and then “turns on” reverse stroke and descends in the same direction from which it rose.
- Mercury has been known to mankind since ancient times. Although the exact date of its discovery is unknown, the first mention of the planet is believed to have appeared around 3000 BC. among the Sumerians.
- A year on Mercury is 88 Earth days long, but a Mercury day is 176 Earth days long. Mercury is almost completely blocked by tidal forces from the Sun, but over time the planet slowly rotates around its axis.
- Mercury orbits the Sun so quickly that some early civilizations believed it was actually two different stars, one of which appears in the morning, and the other in the evening.
- With a diameter of 4.879 km, Mercury is the smallest planet in the solar system and is also one of the five planets that can be seen in the night sky with the naked eye.
- After Earth, Mercury is the second densest planet in the solar system. Despite its small size, Mercury is very dense, as it consists mainly of heavy metals and stone. This allows us to classify it as a terrestrial planet.
- Astronomers did not realize that Mercury was a planet until 1543, when Copernicus created a heliocentric model of the solar system, in which the planets revolve around the sun.
- The gravitational forces of the planet are 38% of the gravitational forces of the Earth. This means that Mercury is unable to retain the atmosphere it has, and what remains is blown away by the solar wind. However, these same solar winds attract gas particles and dust from micrometeorites to Mercury and form radioactive decay, which in some way forms an atmosphere.
- Mercury has no moons or rings due to its low gravity and lack of atmosphere.
- There was a theory that between the orbits of Mercury and the Sun there was an undiscovered planet Vulcan, but its presence was never proven.
- Mercury's orbit is an ellipse, not a circle. It has the most eccentric orbit in the solar system.
- Mercury has only the second highest temperature among the planets in the solar system. The first place is taken
