1. Mercury is the closest planet to the Sun, the smallest and fastest. The average speed of the planet in orbit is 48 km/s.
2. Equatorial Mercury's diameter is 4878 km. Smaller than Jupiter's moon Ganymede and Saturn's moon Titan.
3. The mass of Mercury is 3.3 1023 kg, which is 0.055 Earth masses. By mass, Mercury surpasses the satellites of the giant planets Ganymede and Titan.
4. The average density of Mercury is 5.43 g/cm³(slightly less than the density of the Earth). This density indicates an increased content of metals in its bowels.
5. Surface temperature from -185°С to 430°С.
6. It makes a complete revolution around the Sun in 88 (87.97 Earth days) in an elongated orbit, sometimes moving away from the Sun by 70 million km, while the smallest distance to the Sun is 46 million km.
7. Mercury makes a full rotation around its axis in 58.65 days.. The average time interval between the two upper culminations of the Sun on this planet is 176 days. Interestingly, when it is near perihelion (the closest distance from the Sun), the Sun for an observer on the surface of the planet can move in the opposite direction within 8 days.
8. The periods of rotation around its axis are related to the rotation around the Sun as 3:2. That is, in one Mercury year, the planet manages to turn around its axis by one and a half turns.
9. Distance from Mercury to Earth varies from 82 to 217 million km. For several days, when observed from the Earth, Mercury changes its position relative to the Sun from the west (morning visibility) to the east (evening visibility).
10. Only in 2009, scientists compiled the first complete map of Mercury using images from the Mariner 10 and Messenger spacecraft.

> > Rotation of Mercury

Peculiarities rotation of Mercury around the Sun: speed, period, how much time the planet spends in orbit in the solar system, the length of the day and year with a photo.

Of all the planets, movement and period rotation of Mercury is the most unusual. The fact is that the process of axial revolutions is slow. If the rotation axis of Mercury takes 175.97 days, then it takes 88 days to fly around the Sun. That is, a day is 1,999 times longer than a year. The equatorial speed indicator is 10.892 km/h. This leads to solar days, where 58.647 days are spent per revolution.

If you were visiting the planet, you could watch the Sun rise to half and linger at one point throughout the day. This happens 4 days before perihelion due to the fact that the orbital velocity exceeds the angular velocity, and the star starts the reverse movement.

Rotation of Mercury around the Sun

Let's take a closer look at the rotation of Mercury around the Sun. During one of the Mercury years, the average solar motion reaches two degrees per day in a westerly direction, causing the day to triple its rotation. Movement will change depending on the year. And the moment of aphelion, it will slow down and give 3 degrees per day. But the Sun will also slow down and stop its westward drift, move eastward, and return to the west again. The tilt of Mercury's axis of rotation is shown below.

It should be understood that at the moment of changing the solar speed, the star will increase in the observed size, and then decrease.

The features and speed of rotation of the planet were not known until 1965. Then it was believed that everything depends on the planetary tides to the Sun. The breakthrough was made by Soviet researchers, who in 1962 managed to beat off radio signals from the surface of Mercury. Later, the Americans used Arecibo and confirmed the results, as well as the rotation period, which reached 58.647 days.

Mercury is the first planet in the solar system. Not so long ago, it occupied almost the last place among all 9 planets in terms of its size. But, as we know, under the Moon nothing lasts forever. In 2006, Pluto lost planetary status due to its oversized size. It became known as a dwarf planet. Thus, Mercury is now at the end of a series of cosmic bodies that cut innumerable circles around the Sun. But it's about size. In relation to the Sun, the planet is closest - 57.91 million km. This is the average value. Mercury rotates in an overly elongated orbit, the length of which is 360 million km. That is why it is sometimes further from the Sun, then, on the contrary, closer to it. At perihelion (the point of the orbit closest to the Sun), the planet approaches the flaming star at 45.9 million km. And at aphelion (the farthest point of the orbit), the distance to the Sun increases and equals 69.82 million km.

Regarding the Earth, here the scale is slightly different. Mercury from time to time approaches us up to 82 million km or diverges up to a distance of 217 million km. The smallest figure does not mean at all that the planet can be carefully and for a long time examined in a telescope. Mercury deviates from the Sun by an angular distance of 28 degrees. From here it emerges that this planet can be observed from the Earth just before dawn or after sunset. You can see it almost at the horizon line. Also, you can not see the whole body as a whole, but only half of it. Mercury is rushing in orbit at a speed of 48 km per second. The planet makes a complete revolution around the Sun in 88 Earth days. The value that shows how different an orbit is from a circle is 0.205. The run-up between the plane of the orbit and the plane of the equator is 3 degrees. This suggests that the planet is characterized by minor seasonal changes. Mercury is a terrestrial planet. This also includes Mars, Earth and Venus. All of them have a very high density. The diameter of the planet is 4880 km. As it is not a shame to realize, but here even some satellites of the planets bypassed it. Diameter of the major satellite, Ganymede, which orbits Jupiter, is 5262 km. Titan, a satellite of Saturn, has no less solid appearance. Its diameter is 5150 km. The diameter of Callisto (satellite of Jupiter) is 4820 km. The Moon is the most popular satellite in the solar system. Its diameter is 3474 km.

Earth and Mercury

It turns out that Mercury is not so unpresentable and nondescript. Everything is known in comparison. A small planet loses well in size to the Earth. Compared to our planet, this small cosmic body looks like a fragile creature. Its mass is 18 times less than the earth's, and its volume is 17.8 times. The area of ​​Mercury lags behind the area of ​​the Earth by 6.8 times.

Features of Mercury's orbit

As mentioned above, the planet makes a complete revolution around the Sun in 88 days. It rotates around its axis in 59 Earth days. The average speed is 48 km per second. Mercury moves slower in some parts of its orbit, faster in others. Its maximum speed at perihelion is 59 km per second. The planet tries to skip the closest area to the Sun as soon as possible. At aphelion, Mercury's speed is 39 km per second. The interaction of speed around the axis and speed along the orbit gives a striking effect. For 59 days, any part of the planet is in one position to the starry sky. This section returns to the Sun after 2 Mercurial years or 176 days. From this it turns out that the solar day on the planet is equal to 176 days. At perihelion there is interesting fact. Here, the orbital rotation speed becomes greater than the movement around the axis. This is how the effect of Joshua (the leader of the Jews who stopped the Sun) arises at longitudes that are turned towards the luminary.

Sunrise on the planet

The sun stops and then starts moving in the opposite direction. The luminary tends to the East, completely ignoring the western direction destined for it. This continues for 7 days, until Mercury passes the closest part of its orbit to the Sun. Then its orbital speed begins to decrease, and the movement of the Sun slows down. In the place where the speeds coincide, the luminary stops. A little time passes, and it begins to move in the opposite direction - from east to west. Regarding longitudes, the picture is even more surprising. If people lived here, they would watch two sunsets and two sunrises. Initially, the Sun would have risen, as expected, in the east. In a moment it would stop. After the beginning of the movement back and would disappear over the horizon. After 7 days, it would again shine in the east and make its way to the highest point in the sky without obstacles. Such striking features of the planet's orbit became known in the 60s. Previously, scientists believed that it is always turned to the Sun on one side, and moves around the axis at the same speed as around the yellow star.

The structure of Mercury

Until the first half of the 70s, little was known about its structure. In 1974, in March, the interplanetary station Mariner-10 flew 703 km from the planet. She repeated her maneuver in September of the same year. Now its distance to Mercury was equal to 48 thousand km. And in 1975, the station made another orbit at a distance of 327 km. It is noteworthy that the magnetic field was recorded by the equipment. It did not represent a powerful formation, but compared to Venus, it looked quite significant. Mercury's magnetic field is 100 times smaller than Earth's. Its magnetic axis is 2 degrees out of alignment with the axis of rotation. The presence of such a formation confirms that this object has a core, where this very field is created. Today there is such a scheme for the structure of the planet - Mercury has an iron-nickel hot core and a silicate shell that surrounds it. The core temperature is 730 degrees. The nucleus is large. It contains 70% of the mass of the entire planet. The core diameter is 3600 km. The thickness of the silicate layer is within 650 km.

planet surface

The planet is littered with craters. In some places they are located very densely, in others there are very few of them. The largest crater is Beethoven, its diameter is 625 km. Scientists suggest that the flat terrain is younger than that dotted with many sinkholes. It was formed due to eruptions of lava, which covered all the craters and made the surface even. Here is the largest formation, which is called the Heat Plain. This is an ancient crater with a diameter of 1300 km. It is surrounded by a mountainous ring. It is believed that lava eruptions flooded this place and made it almost invisible. Opposite this plain there are many hills that can reach a height of 2 km. The lowlands are narrow. Apparently, a large asteroid that fell on Mercury provoked a shift in its bowels. In one place a large dent was left, and on the other side the crust rose and thus formed a displacement of rocks and faults. Something similar can be observed in other parts of the planet. These formations have a different geological history. Their shape is wedge-shaped. The width reaches tens of kilometers. It seems that this is a rock that was squeezed out under enormous pressure from the deep bowels.

There is a theory that these creations arose with a decrease in the temperature regimes of the planet. The core began to cool and shrink at the same time. Thus, the top layer also began to decrease. Bark shifts were provoked. This is how this peculiar landscape of the planet was formed. Now the temperature regimes of Mercury also have certain specifics. Given that the planet is close to the Sun, the conclusion follows: the surface that faces the yellow star has too high a temperature. Its maximum can be 430 degrees (at perihelion). In aphelion, respectively, cooler - 290 degrees. In other parts of the orbit, the temperature fluctuates between 320-340 degrees. It is easy to guess that at night the situation here is completely different. At this time, the temperature is kept at minus 180. It turns out that in one part of the planet there is a terrible heat, and in another at the same time it is a terrible cold. An unexpected fact that the planet has reserves of water ice. It is found at the bottom of large craters at polar points. The sun's rays do not penetrate here. Mercury's atmosphere contains 3.5% water. It is delivered to the planet by comets. Some collide with Mercury as they approach the Sun and stay there forever. The ice melts into water and it evaporates into the atmosphere. At cold temperatures, it settles to the surface and turns back into ice. If it was at the bottom of the crater or at the pole, it freezes and does not return to the gaseous state. Since temperature differences are observed here, the conclusion follows: the cosmic body has no atmosphere. More precisely, there is a gas cushion available, but it is too rarefied. The main chemical element of the atmosphere of this planet is helium. It is brought here by the solar wind, a stream of plasma that flows out of the solar corona. Its main constituents are hydrogen and helium. The first is present in the atmosphere, but in a smaller ratio.

Research

Although Mercury is not at a great distance from the Earth, its study is quite difficult. This is due to the peculiarities of the orbit. This planet is very difficult to see in the sky. Only by observing it up close, you can get a complete picture of the planet. In 1974, such an opportunity arose. As already mentioned, this year there was an interplanetary station "Mariner-10" near the planet. She took pictures that mapped nearly half of Mercury's surface. In 2008, the Messenger station honored the planet with attention. Of course, they will continue to study the planet. What surprises it will present, we will see. After all, space is so unpredictable, and its inhabitants are mysterious and secretive.

Facts to know about the planet Mercury:

It is the smallest planet in the solar system.

A day here is 59 days, and a year is 88.

Mercury is the planet closest to the Sun. Distance - 58 million km.

This is a solid planet that belongs to the terrestrial group. Mercury has a heavily cratered, rugged surface.

Mercury has no satellites.

The exosphere of the planet consists of sodium, oxygen, helium, potassium and hydrogen.

There is no ring around Mercury.

There is no evidence of life on the planet. Daytime temperatures reach 430 degrees and drop to minus 180.

From the closest point to the yellow star on the surface of the planet, the Sun appears to be 3 times larger than from Earth.

Mercury is the closest planet to the Sun in the Solar System, orbiting the Sun in 88 Earth days. The duration of one sidereal day on Mercury is 58.65 Earth days, and solar - 176 Earth days. The planet is named after the ancient Roman god of trade, Mercury, an analogue of the Greek Hermes and the Babylonian Naboo.

Mercury belongs to the inner planets, since its orbit lies inside the orbit of the Earth. After depriving Pluto of the status of a planet in 2006, Mercury passed the title of the smallest planet in the solar system. The apparent magnitude of Mercury ranges from 1.9 to 5.5, but it is not easy to see due to its small angular distance from the Sun (maximum 28.3°). Relatively little is known about the planet. Only in 2009, scientists compiled the first complete map of Mercury using images from the Mariner 10 and Messenger spacecraft. The presence of any natural satellites of the planet has not been found.

Mercury is the smallest terrestrial planet. Its radius is only 2439.7 ± 1.0 km, which is less than the radius of Jupiter's moon Ganymede and Saturn's moon Titan. The mass of the planet is 3.3 1023 kg. The average density of Mercury is quite high - 5.43 g/cm, which is only slightly less than the density of the Earth. Considering that the Earth is larger in size, the value of the density of Mercury indicates an increased content of metals in its bowels. The free fall acceleration on Mercury is 3.70 m/s. The second space velocity is 4.25 km/s. Despite its smaller radius, Mercury still surpasses in mass such satellites of the giant planets as Ganymede and Titan.

The astronomical symbol of Mercury is a stylized image of the winged helmet of the god Mercury with his caduceus.

Planet movement

Mercury moves around the Sun in a rather strongly elongated elliptical orbit (eccentricity 0.205) at an average distance of 57.91 million km (0.387 AU). At perihelion, Mercury is 45.9 million km from the Sun (0.3 AU), at aphelion - 69.7 million km (0.46 AU). At perihelion, Mercury is more than one and a half times closer to Sun than at aphelion. The inclination of the orbit to the plane of the ecliptic is 7°. Mercury spends 87.97 Earth days per orbit. The average speed of the planet in orbit is 48 km/s. The distance from Mercury to Earth varies from 82 to 217 million km.

For a long time, it was believed that Mercury is constantly facing the Sun with the same side, and one revolution around its axis takes the same 87.97 Earth days. Observations of details on the surface of Mercury did not contradict this. This misconception was due to the fact that the most favorable conditions for observing Mercury are repeated after a period approximately equal to six times the rotation period of Mercury (352 days), therefore, approximately the same part of the planet's surface was observed at different times. The truth was revealed only in the mid-1960s, when the radar of Mercury was carried out.

It turned out that the Mercury sidereal day is equal to 58.65 Earth days, that is, 2/3 of the Mercury year. Such a commensurability of the periods of rotation around the axis and the revolution of Mercury around the Sun is a unique phenomenon for the solar system. It is presumably due to the fact that the tidal action of the Sun took away the angular momentum and slowed down the rotation, which was initially faster, until the two periods were connected by an integer ratio. As a result, in one Mercury year, Mercury has time to rotate around its axis by one and a half turns. That is, if at the moment Mercury passes perihelion, a certain point of its surface faces exactly the Sun, then during the next passage of perihelion, exactly the opposite point of the surface will face the Sun, and after another Mercury year, the Sun will again return to the zenith over the first point. As a result, a solar day on Mercury lasts two Mercury years or three Mercury sidereal days.

As a result of such a movement of the planet, “hot longitudes” can be distinguished on it - two opposite meridians, which alternately face the Sun during the passage of perihelion by Mercury, and on which, because of this, it is especially hot even by Mercury standards.

There are no such seasons on Mercury as there are on Earth. This is due to the fact that the axis of rotation of the planet is at right angles to the plane of the orbit. As a result, there are areas near the poles that the sun's rays never reach. A survey conducted by the Arecibo radio telescope suggests that there are glaciers in this cold and dark zone. The glacial layer can reach 2 m and is covered with a layer of dust.

The combination of the movements of the planet gives rise to another unique phenomenon. The speed of rotation of the planet around its axis is practically constant, while the speed of orbital motion is constantly changing. In the segment of the orbit near the perihelion, for about 8 days, the angular velocity of the orbital motion exceeds the angular velocity rotary motion. As a result, the Sun in the sky of Mercury stops and begins to move in the opposite direction - from west to east. This effect is sometimes called the Joshua effect, after the biblical protagonist Joshua, who stopped the Sun from moving (Joshua 10:12-13). For an observer at longitudes 90° away from the "hot longitudes", the Sun rises (or sets) twice.

It is also interesting that, although Mars and Venus are the closest orbits to Earth, Mercury is more often than others the planet closest to Earth (because others move away to a greater extent, not being so "tied" to the Sun).

Anomalous orbit precession

Mercury is close to the Sun, so the effects of the general theory of relativity are manifested in its movement to the greatest extent among all the planets of the solar system. As early as 1859, the French mathematician and astronomer Urbain Le Verrier reported that there was a slow precession in Mercury's orbit that could not be fully explained by calculating the effects of known planets according to Newtonian mechanics. Mercury's perihelion precession is 5600 arc seconds per century. The calculation of the influence of all other celestial bodies on Mercury according to Newtonian mechanics gives a precession of 5557 arc seconds per century. In an attempt to explain the observed effect, he suggested that there was another planet (or perhaps a belt of small asteroids), whose orbit is closer to the Sun than that of Mercury, and which introduces a perturbing influence (other explanations considered the unaccounted for polar oblateness of the Sun). Thanks to previous successes in the search for Neptune, taking into account its influence on the orbit of Uranus, this hypothesis became popular, and the hypothetical planet we were looking for was even named Vulcan. However, this planet has never been discovered.

Since none of these explanations stood the test of observation, some physicists began to put forward more radical hypotheses that it is necessary to change the law of gravity itself, for example, change the exponent in it or add terms depending on the speed of bodies to the potential. However, most of these attempts have proved contradictory. At the beginning of the 20th century, general relativity provided an explanation for the observed precession. The effect is very small: the relativistic “add-on” is only 42.98 arcseconds per century, which is 1/130 (0.77%) of the total precession rate, so it would take at least 12 million revolutions of Mercury around the Sun for perihelion to return to the position predicted by the classical theory. A similar, but smaller displacement exists for other planets - 8.62 arc seconds per century for Venus, 3.84 for the Earth, 1.35 for Mars, as well as asteroids - 10.05 for Icarus.

Hypotheses for the formation of Mercury

Since the 19th century, there has been a scientific hypothesis that Mercury was a satellite of the planet Venus in the past, which was subsequently “lost” by it. In 1976, Tom van Flandern (English) Russian. and K. R. Harrington, on the basis of mathematical calculations, it was shown that this hypothesis explains well the large deviations (eccentricity) of Mercury's orbit, its resonant nature of circulation around the Sun and the loss of rotational momentum for both Mercury and Venus (the latter also - the acquisition of rotation, the opposite of the main one in the solar system).

At present, this hypothesis is not confirmed by observational data and information from automatic stations of the planet. The presence of a massive iron core with a large amount of sulfur, the percentage of which is greater than in the composition of any other planet in the solar system, the features of the geological and physico-chemical structure of the surface of Mercury indicate that the planet was formed in the solar nebula independently of other planets, that is Mercury has always been an independent planet.

Now there are several versions to explain the origin of the huge core, the most common of which says that Mercury initially had the ratio of the mass of metals to the mass of silicates was similar to those in the most common meteorites - chondrites, the composition of which is generally typical for solid bodies of the solar system and internal planets, and the mass of the planet in ancient times was approximately 2.25 times its present mass. In the history of the early solar system, Mercury may have experienced a collision with a planetesimal of approximately 1/6 of its own mass at a speed of ~20 km/s. Most of the crust and the upper layer of the mantle was blown into outer space, which, having been crushed into hot dust, dissipated in interplanetary space. And the core of the planet, consisting of heavier elements, has been preserved.

According to another hypothesis, Mercury was formed in the inner part of the protoplanetary disk, already extremely depleted in light elements, which were swept out by the Sun into the outer regions of the solar system.

Surface

In its physical characteristics, Mercury resembles the Moon. The planet has no natural satellites, but has a very rarefied atmosphere. The planet has a large iron core, which is the source of the magnetic field in its totality, which is 0.01 of the earth's. Mercury's core makes up 83% of the planet's total volume. The temperature on the surface of Mercury ranges from 90 to 700 K (+80 to +430 °C). The solar side heats up much more than the polar regions and the far side of the planet.

The surface of Mercury also in many ways resembles that of the moon - it is heavily cratered. The density of craters varies in different areas. It is assumed that the more densely cratered areas are older, and the less densely dotted areas are younger, formed when the old surface was flooded with lava. At the same time, large craters are less common on Mercury than on the Moon. The largest crater on Mercury is named after the great Dutch painter Rembrandt, its diameter is 716 km. However, the similarity is incomplete - on Mercury, formations are visible that are not found on the Moon. An important difference between the mountainous landscapes of Mercury and the Moon is the presence on Mercury of numerous jagged slopes stretching for hundreds of kilometers - scarps. The study of their structure showed that they were formed during the compression that accompanied the cooling of the planet, as a result of which the surface area of ​​Mercury decreased by 1%. The presence of well-preserved large craters on the surface of Mercury suggests that over the past 3-4 billion years there has not been a large-scale movement of sections of the crust there, and there was also no surface erosion, the latter almost completely excludes the possibility of the existence of anything significant in the history of Mercury. atmosphere.

In the course of research conducted by the Messenger probe, more than 80% of the surface of Mercury was photographed and found to be homogeneous. In this, Mercury is not like the Moon or Mars, in which one hemisphere differs sharply from the other.

The first data on the study of the elemental composition of the surface using the X-ray fluorescence spectrometer of the Messenger apparatus showed that it is poor in aluminum and calcium compared to plagioclase feldspar, characteristic of the continental regions of the Moon. At the same time, the surface of Mercury is relatively poor in titanium and iron and rich in magnesium, occupying an intermediate position between typical basalts and ultramafic rocks type of terrestrial komatiites. A comparative abundance of sulfur has also been found, suggesting reducing conditions for the formation of the planet.

craters

Craters on Mercury range in size from small bowl-shaped depressions to multi-ringed impact craters hundreds of kilometers across. They are in various stages of destruction. There are relatively well-preserved craters with long rays around them, which were formed as a result of the ejection of material at the moment of impact. There are also heavily destroyed remains of craters. Mercury craters differ from lunar craters in that the area of ​​their cover from the release of matter upon impact is smaller due to the greater gravity on Mercury.

One of the most noticeable details of the surface of Mercury is the Heat Plain (lat. Caloris Planitia). This feature of the relief got its name because it is located near one of the "hot longitudes". Its diameter is about 1550 km.

Probably, the body, upon impact of which the crater was formed, had a diameter of at least 100 km. The impact was so strong that seismic waves, passing the entire planet and focusing at the opposite point of the surface, led to the formation here of a kind of crossed "chaotic" landscape. Also testifying to the force of the impact is the fact that it caused the ejection of lava, which formed high concentric circles at a distance of 2 km around the crater.

The point with the highest albedo on the surface of Mercury is the Kuiper crater with a diameter of 60 km. This is probably one of the "youngest" large craters on Mercury.

Until recently, it was assumed that in the bowels of Mercury there is a metal core with a radius of 1800-1900 km, containing 60% of the mass of the planet, since the Mariner-10 spacecraft detected a weak magnetic field, and it was believed that a planet with such a small size could not have a liquid kernels. But in 2007, Jean-Luc Margot's group summed up five years of radar observations of Mercury, during which they noticed variations in the planet's rotation, too large for a model with a solid core. Therefore, today it is possible to say with a high degree of certainty that the core of the planet is liquid.

The percentage of iron in the core of Mercury is higher than that of any other planet in the solar system. Several theories have been proposed to explain this fact. According to the most widely supported theory in the scientific community, Mercury originally had the same ratio of metal to silicates as an ordinary meteorite, having a mass 2.25 times what it is now. However, at the beginning of the history of the solar system, a planet-like body hit Mercury, having 6 times less mass and several hundred kilometers in diameter. As a result of the impact, most of the original crust and mantle separated from the planet, due to which the relative proportion of the core in the planet increased. A similar process, known as the giant impact theory, has been proposed to explain the formation of the moon. However, the first data of the study of the elemental composition of the surface of Mercury using the gamma-ray spectrometer AMS "Messenger" do not confirm this theory: the abundance of the radioactive isotope potassium-40 of the moderately volatile chemical element potassium compared to radioactive isotopes thorium-232 and uranium-238 over the refractory elements uranium and thorium do not dock with high temperatures, inevitable in a collision. Therefore, it is assumed that the elemental composition of Mercury corresponds to the primary elemental composition of the material from which it was formed, close to enstatite chondrites and anhydrous cometary particles, although the iron content in the enstatite chondrites studied so far is insufficient to explain the high average density of Mercury.

The core is surrounded by a silicate mantle 500-600 km thick. According to data from Mariner 10 and observations from Earth, the thickness of the planet's crust is from 100 to 300 km.

Geological history

Like the Earth, Moon, and Mars, Mercury's geological history is divided into eras. They have the following names (from earlier to later): pre-Tolstoy, Tolstoy, Kalorian, late Kalorian, Mansurian and Kuiper. This division periodizes the relative geological age of the planet. The absolute age, measured in years, is not precisely established.

After the formation of Mercury 4.6 billion years ago, there was an intense bombardment of the planet by asteroids and comets. The last strong bombardment of the planet occurred 3.8 billion years ago. Some regions, such as the Plain of Heat, were also formed due to their filling with lava. This led to the formation of smooth planes inside the craters, like the moon.

Then, as the planet cooled and contracted, ridges and rifts began to form. They can be observed on the surface of larger details of the planet's relief, such as craters, plains, which indicates a later time of their formation. Mercury's volcanic period ended when the mantle contracted enough to prevent lava from escaping to the planet's surface. This probably happened in the first 700-800 million years of its history. All subsequent changes in the relief are caused by impacts of external bodies on the surface of the planet.

A magnetic field

Mercury has magnetic field, the intensity of which is 100 times less than that of the earth. The magnetic field of Mercury has a dipole structure and in the highest degree symmetrically, and its axis deviates by only 10 degrees from the axis of rotation of the planet, which imposes a significant limitation on the range of theories explaining its origin. The magnetic field of Mercury is possibly formed as a result of the dynamo effect, that is, in the same way as on Earth. This effect is the result of the circulation of the liquid core of the planet. Due to the pronounced eccentricity of the planet, an extremely strong tidal effect occurs. It maintains the core in a liquid state, which is necessary for the manifestation of the dynamo effect.

Mercury's magnetic field is strong enough to change the direction of the solar wind around the planet, creating a magnetosphere. The planet's magnetosphere, though small enough to fit inside the Earth, is powerful enough to trap solar wind plasma. The results of observations obtained by Mariner 10 detected low-energy plasma in the magnetosphere on the night side of the planet. Explosions of active particles have been detected in the magnetotail, which indicates the dynamic qualities of the planet's magnetosphere.

During its second flyby on October 6, 2008, Messenger discovered that Mercury's magnetic field may have a significant number of windows. The spacecraft encountered the phenomenon of magnetic vortices - woven knots of the magnetic field connecting the spacecraft with the magnetic field of the planet. The vortex reached 800 km across, which is a third of the radius of the planet. This vortex form of the magnetic field is created by the solar wind. As the solar wind flows around the planet's magnetic field, it binds and sweeps with it, curling into vortex-like structures. These magnetic flux vortices form windows in the planetary magnetic shield through which the solar wind enters and reaches the surface of Mercury. The process of linking the planetary and interplanetary magnetic fields, called magnetic reconnection, is a common occurrence in space. It also occurs near the Earth when it generates magnetic vortices. However, according to the observations of "Messenger", the frequency of reconnection of the magnetic field of Mercury is 10 times higher.

Conditions on Mercury

The proximity to the Sun and the rather slow rotation of the planet, as well as an extremely weak atmosphere, lead to the fact that Mercury experiences the most dramatic temperature changes in the solar system. This is also facilitated by the loose surface of Mercury, which conducts heat poorly (and with a completely absent or extremely weak atmosphere, heat can be transferred deep into only due to heat conduction). The surface of the planet quickly heats up and cools down, but already at a depth of 1 m, daily fluctuations cease to be felt, and the temperature becomes stable, equal to approximately +75 ° C.

The average temperature of its daytime surface is 623 K (349.9 °C), the nighttime temperature is only 103 K (170.2 °C). The minimum temperature on Mercury is 90 K (183.2 ° C), and the maximum reached at noon at "hot longitudes" when the planet is near perihelion is 700 K (426.9 ° C).

Despite these conditions, in Lately there were suggestions that ice could exist on the surface of Mercury. Radar studies of the subpolar regions of the planet showed the presence of depolarization areas there from 50 to 150 km, the most likely candidate for a substance reflecting radio waves may be ordinary water ice. Entering the surface of Mercury when comets hit it, the water evaporates and travels around the planet until it freezes in the polar regions at the bottom of deep craters, where the Sun never looks, and where ice can remain almost indefinitely.

During the flight of the Mariner-10 spacecraft past Mercury, it was established that the planet has an extremely rarefied atmosphere, the pressure of which is 5 1011 times less than the pressure of the earth's atmosphere. Under such conditions, atoms collide with the surface of the planet more often than with each other. The atmosphere is made up of atoms captured from the solar wind or knocked out by the solar wind from the surface - helium, sodium, oxygen, potassium, argon, hydrogen. The average lifetime of an individual atom in the atmosphere is about 200 days.

Hydrogen and helium are likely brought to the planet by the solar wind, diffusing into its magnetosphere and then escaping back into space. The radioactive decay of elements in Mercury's crust is another source of helium, sodium and potassium. Water vapor is present, released as a result of a number of processes, such as impacts of comets on the surface of the planet, the formation of water from the hydrogen of the solar wind and the oxygen of rocks, sublimation from ice, which is located in permanently shadowed polar craters. Finding a significant number of ions related to water, such as O+, OH+ H2O+, came as a surprise.

Since a significant number of these ions have been found in space surrounding Mercury, scientists have suggested that they were formed from water molecules destroyed on the surface or in the exosphere of the planet by the solar wind.

On February 5, 2008, a group of astronomers from Boston University, led by Jeffrey Baumgardner, announced the discovery of a comet-like tail around the planet Mercury, more than 2.5 million km long. It was discovered during observations from ground-based observatories in the sodium line. Prior to this, a tail no longer than 40,000 km was known. The first image was taken by this group in June 2006 with a 3.7-meter telescope. Air force USA on Mount Haleakala (Hawaii), and then used three more smaller instruments: one at Haleakala and two at the McDonald Observatory (Texas). A telescope with a 4-inch (100 mm) aperture was used to create an image with a large field of view. An image of Mercury's long tail was taken in May 2007 by Jody Wilson (Senior Scientist) and Carl Schmidt (PhD student). The apparent length of the tail for an observer from Earth is about 3°.

New data on the tail of Mercury appeared after the second and third flybys of the Messenger spacecraft in early November 2009. Based on these data, NASA employees were able to offer a model of this phenomenon.

Features of observation from the Earth

The apparent magnitude of Mercury ranges from -1.9 to 5.5, but is not easy to see due to its small angular distance from the Sun (maximum 28.3°). At high latitudes, the planet can never be seen in the dark night sky: Mercury is visible for a very short time after dusk. The optimal time for observing the planet is morning or evening twilight during periods of its elongations (periods of maximum removal of Mercury from the Sun in the sky, occurring several times a year).

The most favorable conditions for observing Mercury are at low latitudes and near the equator: this is due to the fact that the duration of twilight is the shortest there. In middle latitudes, finding Mercury is much more difficult and possible only during the period of the best elongations, and in high latitudes it is impossible at all. The most favorable conditions for observing Mercury in the middle latitudes of both hemispheres are around the equinoxes (the duration of twilight is minimal).

The earliest known sighting of Mercury was recorded in the Mul Apin (a collection of Babylonian astrological tables). This observation was most likely made by Assyrian astronomers around the 14th century BC. e. The Sumerian name used for Mercury in the Mul apin tables can be transcribed as UDU.IDIM.GUU4.UD ("leaping planet"). Initially, the planet was associated with the god Ninurta, and in later records it is called "Nabu" in honor of the god of wisdom and scribal art.

V Ancient Greece in the time of Hesiod, the planet was known under the names ("Stilbon") and ("Hermaon"). The name "Hermaon" is a form of the name of the god Hermes. Later, the Greeks began to call the planet "Apollo".

There is a hypothesis that the name "Apollo" corresponded to visibility in the morning sky, and "Hermes" ("Hermaon") in the evening. The Romans named the planet after the fleet-footed god of commerce Mercury, who is equivalent to the Greek god Hermes, for moving across the sky faster than the other planets. The Roman astronomer Claudius Ptolemy, who lived in Egypt, wrote about the possibility of a planet moving through the disk of the Sun in his work Hypotheses about the Planets. He suggested that such a transit has never been observed because a planet like Mercury is too small to observe or because the moment of transit does not occur often.

In ancient China, Mercury was called Chen-xing, "Morning Star". It was associated with the direction of the north, the color black and the element of water in Wu-sin. According to the "Hanshu", the synodic period of Mercury by Chinese scientists was recognized as equal to 115.91 days, and according to the "Hou Hanshu" - 115.88 days. In modern Chinese, Korean, Japanese and Vietnamese cultures, the planet began to be called "Water Star".

Indian mythology used the name Budha for Mercury. This god, the son of Soma, was presiding on Wednesdays. In Germanic paganism, the god Odin was also associated with the planet Mercury and with the environment. The Maya Indians represented Mercury as an owl (or perhaps as four owls, two corresponding to the morning appearance of Mercury, and two to the evening), which was a messenger afterlife. In Hebrew, Mercury was called "Koch in Ham".
Mercury on starry sky(above, above the Moon and Venus)

In the Indian astronomical treatise "Surya Siddhanta", dated to the 5th century, the radius of Mercury was estimated at 2420 km. The error compared to the true radius (2439.7 km) is less than 1%. However, this estimate was based on an inaccurate assumption about the planet's angular diameter, which was taken as 3 arc minutes.

In medieval Arabic astronomy, the Andalusian astronomer Az-Zarkali described the deferent of Mercury's geocentric orbit as an oval like an egg or a pine nut. However, this conjecture had no effect on his astronomical theory and his astronomical calculations. In the 12th century, Ibn Baja observed two planets as spots on the surface of the Sun. Later, the astronomer of the Maraga observatory Ash-Shirazi suggested that his predecessor observed the passage of Mercury and (or) Venus. In India, the astronomer of the Kerala school, Nilakansa Somayaji (English) Russian. In the 15th century, he developed a partially heliocentric planetary model in which Mercury revolved around the Sun, which, in turn, revolved around the Earth. This system was similar to that of Tycho Brahe developed in the 16th century.

Medieval observations of Mercury in the northern parts of Europe were hampered by the fact that the planet is always observed at dawn - morning or evening - against the background of the twilight sky and rather low above the horizon (especially in northern latitudes). The period of its best visibility (elongation) occurs several times a year (lasting about 10 days). Even during these periods, it is not easy to see Mercury with the naked eye (a relatively dim star against a fairly light sky background). There is a story that Nicolaus Copernicus, who observed astronomical objects in the northern latitudes and foggy climate of the Baltic states, regretted that he had not seen Mercury in his entire life. This legend was formed based on the fact that Copernicus' work "On the rotations of the celestial spheres" does not give a single example of observations of Mercury, but he described the planet using the results of observations of other astronomers. As he himself said, Mercury can still be "caught" from the northern latitudes, showing patience and cunning. Consequently, Copernicus could well observe Mercury and observed it, but he made the description of the planet based on other people's research results.

Telescope observations

The first telescopic observation of Mercury was made by Galileo Galilei at the beginning of the 17th century. Although he observed the phases of Venus, his telescope was not powerful enough to observe the phases of Mercury. In 1631, Pierre Gassendi made the first telescopic observation of the passage of a planet across the solar disk. The moment of passage was calculated before by Johannes Kepler. In 1639, Giovanni Zupi discovered with a telescope that the orbital phases of Mercury are similar to those of the Moon and Venus. Observations have definitively demonstrated that Mercury revolves around the Sun.

A very rare astronomical event is the overlapping of one planet's disk by another, observed from Earth. Venus overlaps Mercury every few centuries, and this event was observed only once in history - May 28, 1737 by John Bevis at the Royal Greenwich Observatory. The next Venus occultation of Mercury will be December 3, 2133.

The difficulties accompanying the observation of Mercury led to the fact that for a long time it was studied less than the other planets. In 1800, Johann Schroeter, who observed the details of the surface of Mercury, announced that he had observed mountains 20 km high on it. Friedrich Bessel, using Schroeter's sketches, erroneously determined the period of rotation around its axis at 24 hours and the tilt of the axis at 70 °. In the 1880s, Giovanni Schiaparelli mapped the planet more accurately and proposed a rotation period of 88 days, coinciding with the sidereal orbital period around the Sun due to tidal forces. The work of mapping Mercury was continued by Eugène Antoniadi, who published a book in 1934 presenting old maps and his own observations. Many features on the surface of Mercury are named after Antoniadi's maps.

Italian astronomer Giuseppe Colombo noticed that the period of rotation is 2/3 of the sidereal period of Mercury, and suggested that these periods fall into a 3: 2 resonance. Data from Mariner 10 subsequently confirmed this view. This does not mean that the maps of Schiaparelli and Antoniadi are wrong. It's just that astronomers saw the same details of the planet every second revolution around the Sun, entered them into maps and ignored observations at the time when Mercury was turned to the Sun by the other side, because due to the geometry of the orbit at that time the conditions for observation were bad.

The proximity of the Sun creates some problems for the telescopic study of Mercury. So, for example, the Hubble telescope has never been used and will not be used to observe this planet. Its device does not allow observations of objects close to the Sun - if you try to do this, the equipment will receive irreversible damage.

Mercury exploration modern methods

Mercury is the least explored terrestrial planet. Telescopic methods of its study in the 20th century were supplemented by radio astronomy, radar and research using spacecraft. Radio astronomy measurements of Mercury were first made in 1961 by Howard, Barrett and Haddock using a reflector with two radiometers mounted on it. By 1966, based on the accumulated data, quite good estimates of the surface temperature of Mercury were obtained: 600 K in the subsolar point and 150 K on the unlit side. The first radar observations were carried out in June 1962 by the group of V. A. Kotelnikov at the IRE, they revealed the similarity of the reflective properties of Mercury and the Moon. In 1965, similar observations at the Arecibo radio telescope made it possible to obtain an estimate of the rotation period of Mercury: 59 days.

Only two spacecraft have been sent to study Mercury. The first was Mariner 10, which flew past Mercury three times in 1974-1975; the maximum approach was 320 km. As a result, several thousand images were obtained, covering approximately 45% of the planet's surface. Further studies from Earth showed the possibility of the existence of water ice in polar craters.

Of all the planets visible to the naked eye, only Mercury has never had its own artificial satellite. NASA is currently on a second mission to Mercury called Messenger. The device was launched on August 3, 2004, and in January 2008 it made its first flyby of Mercury. To enter orbit around the planet in 2011, the device made two more gravitational maneuvers near Mercury: in October 2008 and in September 2009. Messenger also performed one gravity assist near Earth in 2005 and two maneuvers near Venus, in October 2006 and June 2007, during which it tested equipment.

Mariner 10 is the first spacecraft to reach Mercury.

The European Space Agency (ESA), together with the Japanese Aerospace Research Agency (JAXA), is developing the Bepi Colombo mission, which consists of two spacecraft: Mercury Planetary Orbiter (MPO) and Mercury Magnetospheric Orbiter (MMO). The European MPO will explore Mercury's surface and depths, while the Japanese MMO will observe the planet's magnetic field and magnetosphere. The launch of BepiColombo is planned for 2013, and in 2019 it will go into orbit around Mercury, where it will be divided into two components.

The development of electronics and informatics made possible ground-based observations of Mercury using CCD radiation receivers and subsequent computer processing of images. One of the first series of observations of Mercury with CCD receivers was carried out in 1995-2002 by Johan Varell at the observatory on the island of La Palma with a half-meter solar telescope. Varell chose the best of the shots without using computer mixing. The reduction began to be applied at the Abastumani Astrophysical Observatory to the series of photographs of Mercury obtained on November 3, 2001, as well as at the Skinakas Observatory of the University of Heraklion to the series from May 1-2, 2002; to process the results of observations, the method of correlation matching was used. The obtained resolved image of the planet was similar to the Mariner-10 photomosaic, the outlines of small formations 150-200 km in size were repeated. This is how the map of Mercury was drawn up for longitudes 210-350°.

March 17, 2011 interplanetary probe "Messenger" (eng. Messenger) entered the orbit of Mercury. It is assumed that with the help of the equipment installed on it, the probe will be able to explore the landscape of the planet, the composition of its atmosphere and surface; The Messenger equipment also makes it possible to conduct studies of energetic particles and plasma. The life of the probe is defined as one year.

On June 17, 2011, it became known that, according to the first studies conducted by the Messenger spacecraft, the planet's magnetic field is not symmetrical about the poles; thus, different numbers of solar wind particles reach the north and south poles of Mercury. We also analyzed the prevalence chemical elements on the planet.

Nomenclature features

The rules for naming geological objects located on the surface of Mercury were approved at the XV General Assembly of the International Astronomical Union in 1973:
The small crater Hun Kal (indicated by the arrow), which serves as the reference point for the longitude system of Mercury. Photo AMS "Mariner-10"

The largest object on the surface of Mercury, with a diameter of about 1300 km, was given the name Heat Plain, since it is located in the region of maximum temperatures. This is a multi-ring structure of impact origin, filled with solidified lava. Another plain, located in the region of minimum temperatures, near the north pole, is called the Northern Plain. The rest of these formations were called the planet Mercury or the analogue of the Roman god Mercury in languages different peoples peace. For example: Suisei Plain (planet Mercury in Japanese) and Budha Plain (planet Mercury in Hindi), Sobkou Plain (planet Mercury among the ancient Egyptians), Plain Odin (Scandinavian god) and Plain Tir (ancient Armenian deity).
Mercury's craters (with two exceptions) are named after famous people in the humanitarian field of activity (architects, musicians, writers, poets, philosophers, photographers, artists). For example: Barma, Belinsky, Glinka, Gogol, Derzhavin, Lermontov, Mussorgsky, Pushkin, Repin, Rublev, Stravinsky, Surikov, Turgenev, Feofan Grek, Fet, Tchaikovsky, Chekhov. The exceptions are two craters: Kuiper, named after one of the main developers of the Mariner 10 project, and Hun Kal, which means the number "20" in the language of the Mayan people, who used a vigesimal number system. The last crater is located near the equator at the meridian of 200 west longitude and was chosen as a convenient reference point for reference in the coordinate system of the surface of Mercury. Initially, the larger craters were given the names of celebrities who, according to the IAU, had respectively greater value in world culture. The larger the crater, the stronger the influence of the individual on modern world. The top five included Beethoven (diameter 643 km), Dostoevsky (411 km), Tolstoy (390 km), Goethe (383 km) and Shakespeare (370 km).
Scarps (ledges), mountain ranges and canyons receive the names of the ships of explorers who have gone down in history, since the god Mercury / Hermes was considered the patron saint of travelers. For example: Beagle, Dawn, Santa Maria, Fram, Vostok, Mirny). An exception to the rule are two ridges named after astronomers, the Antoniadi Ridge and the Schiaparelli Ridge.
Valleys and other features on the surface of Mercury are named after major radio observatories, in recognition of the importance of radar in exploring the planet. For example: Highstack Valley (radio telescope in the USA).
Subsequently, in connection with the discovery in 2008 by the automatic interplanetary station "Messenger" of furrows on Mercury, a rule was added for naming furrows, which receive the names of great architectural structures. For example: The Pantheon in the Plain of Heat.

So, what is the planet Mercury and what is so special about it that distinguishes it from other planets? Probably, first of all, it is worth listing the most obvious that can be easily gleaned from different sources, but without which it will be difficult for a person to compose an overall picture.

At the moment (after Pluto was "demoted" to a dwarf planet), 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 makes a revolution around our star much faster than other planets. Apparently, it was the latter quality that served as the reason to name her in honor of the fastest messenger of the Gods named Mercury, an outstanding 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 the "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 make their rotation around the Sun, and not around.

Mercury today

Nowadays, scientists know that due to the close proximity of Mercury to the Sun, the temperature on its surface can reach up to 450 degrees Celsius. But the absence 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 day and night on Mercury turned out to be the highest in the solar system - more than 600 degrees Celsius.

In size, Mercury is slightly larger 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 that, 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, mankind 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. At the same time, the vacuum in the atmosphere of this planet is much closer to the true vacuum, if compared with any other vacuum created on Earth using technical means.

There are two explanations for the absence of an atmosphere on Mercury. First, it 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 most 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 blow away the last remnants of what can be called an atmosphere.

However, no matter how poor the atmosphere on this planet is, it still exists. According to the NASA space agency, 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 is made up of molecules of argon, carbon dioxide, water, nitrogen, xenon, krypton, neon, calcium (Ca, Ca +) and magnesium.

It is believed that the rarefied atmosphere is due to the presence of extreme temperatures on the surface of the planet. The lowest temperature can be around -180°C and the highest around 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 just 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, leaving unhindered into outer space.

Until 1974, the surface of Mercury remained largely a mystery. Observations of this cosmic body from the Earth were very difficult due to the proximity of the planet to the Sun. It was possible to consider Mercury only before dawn or immediately after sunset, but on Earth at this time the line of sight is significantly limited by too dense layers of the atmosphere of our planet.

But in 1974, after a magnificent three-time flyby of the surface of Mercury by the Mariner 10 spacecraft, the first sufficiently 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 the analysis of 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 "Kaloris" 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. It is believed that these smooth areas of the surface were created as a result of the movement of lava flows through the planet in the past.

And, finally, the third feature is the rocks scattered over 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 active volcanic activity was once present in the historical past of the planet. However, the number and age of the craters, on the contrary, indicate that Mercury was geologically passive for a very long time.

But no less interesting is the third distinguishing feature the surface of Mercury. It turned out that the hills are formed by the activity of the planet's core, as a result of which the so-called "buckling" of the crust occurs. Such bulges on Earth are usually associated with the displacement of tectonic plates, while the loss of stability of the crust of Mercury occurs due to the contraction of its core, which is gradually compressed. The processes occurring with the core of the planet lead to the contraction of the planet itself. The latest 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: crust, mantle, and 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, reminiscent of the earth in their shape, indicates that, despite sufficient hardness, 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 in the past there was a collision of the planet with a huge planetesmial, which led to the loss of a significant mass of the mantle.

The core of Mercury has become the subject of many studies. 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 of Titan, whose diameter is 5125 kilometers and the satellite of 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 tried to explain this feature of the planet's core, and cast doubt on the fact that the core of Mercury is actually solid. By measuring the features of the rebound of radio waves from the surface of the planet, a group of planetary scientists came to the conclusion that the core of the planet is actually liquid and this explains a lot.

Orbit and rotation of Mercury

Mercury is much closer to the Sun than any other planet in our system and, accordingly, it needs the most a short time for orbital rotation. 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. Also, of all the planetary orbits, Mercury's orbit is the least circular.
This eccentricity, along with the absence of a significant atmosphere, explains why the surface of Mercury has the widest range of extreme temperatures in the solar system. Simply put, the surface of Mercury heats up much more when the planet is at perihelion than when it is at aphelion, since the difference in distance between these points is too great.

The orbit of Mercury itself is a perfect example of one of the leading processes in modern physics. It's about about a process called precession, which explains the shift in Mercury's orbit relative to the Sun over time.

Although Newtonian mechanics (i.e. classical physics) predicts the rates of this precession in great detail, the exact values ​​have not been determined. This became a real problem for astronomers in the late nineteenth and early twentieth centuries. In order to explain the difference between theoretical interpretations and actual observations, many concepts have been drawn up. According to one theory, it has even been suggested that there is an unknown planet whose orbit is closer to the Sun than that of Mercury.

However, the most plausible explanation came after Einstein's general theory of relativity was published. 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 the spin-orbital resonance of Mercury (the number of revolutions in the orbit) was 1:1, but, in the end, it was proved that in fact it is 3:2. It is thanks to this resonance that a phenomenon is possible on the planet that is impossible on Earth. If the observer were on Mercury, he could see that the Sun rises to the highest point in the sky, and then "turns on" the reverse motion and descends in the same direction from which it rose.

1. Mercury has been known to mankind since ancient times. Though exact date its discovery is unknown, the first mention of the planet is believed to have appeared around 3000 BC. at the Sumerians.
2. A year on Mercury is 88 Earth days, but a Mercury day is 176 Earth days. Mercury is almost completely blocked by the Sun's tidal forces, but over time it makes a slow rotation of the planet around its axis.
3. Mercury revolves so fast around the sun that some early civilizations believed that they were actually two different stars, one of which appears in the morning and the other in the evening.
4. 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.
5. 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 attribute it to the terrestrial planets.
6. Astronomers did not realize that Mercury was a planet until 1543, when Copernicus created the heliocentric model of the solar system, according to which the planets revolve around the sun.
7. The gravitational forces of the planet are 38% of the gravitational forces of the Earth. This means that Mercury is unable to hold on to the atmosphere it has, and what is left is blown away by the solar wind. However, all the same solar winds attract gas particles to Mercury, dust from micrometeorites and form radioactive decay, which in some way forms an atmosphere.
8. Mercury has no moons or rings due to its low gravity and lack of an atmosphere.
9. There was a theory that between the orbits of Mercury and the Sun there is the still undiscovered planet Vulcan, but its presence has never been proven.
10. Mercury's orbit is an ellipse, not a circle. It has the most eccentric orbit in the solar system.
11. Mercury is only the second hottest planet in the solar system. The first place is