Planet characteristics:
- Distance from the Sun: 57.9 million km
- Planet Diameter: 4878 km
- Days on the planet: 58 days 16 o'clock*
- Year on the planet: 88 days*
- t° on the surface: -180°C to +430°C
- Atmosphere: almost not present
- Satellites: does not have
* period of rotation around its own axis (in Earth days)
** orbital period around the Sun (in Earth days)
Mercury is the eighth largest planet and the closest to the Sun, with an average distance of 0.387 AU (astronomical units) or 57,910,000 kilometers. The mass of the planet is 3.30e23 kg, and the diameter is 4.880 km (only Pluto is smaller).
Presentation: planet Mercury
Internal structure
In the center of the planet is a metal core, similar to the earth, the difference is only in size. If the earth's core occupies only 17% of the planet's volume, then Mercury has 42% of the volume.
Around the core is a mantle layer - 500-700 kilometers of silicate rock. The next layer is the crust, which is about 100-300 kilometers thick. The upper layer of the planet has a lot of damage, most scientists adhere to the theory that they arose due to the slow cooling of Mercury.
atmosphere and surface
The atmosphere of Mercury is very rarefied and practically equates to a vacuum. Compound:
- hydrogen (70 atoms per 1 cm³);
- helium (4,500 atoms per 1 cm³).
Due to the almost zero atmosphere and proximity to the Sun, the temperature on the planet's surface fluctuates between -180….+440 °C. The surface resembles the lunar one - many craters (from a collision with asteroids), and mountains up to 4 km high (lunar ones can be one and a half times higher).
Unlike the Earth's satellite, on the reverse side of Mercury there are swellings that were formed under the influence of solar tides. There are also high ledges, whose length can reach several hundred kilometers.
The name of the planet was given by the ancient Romans, who revered the god Mercury as the patron of thieves, travelers and merchants. However, it is believed that the first planet from the Sun was known as early as 3000 BC. (from the time of the Samaritans).
In ancient Greece, she was called by two names at once - Apollo (god of sunlight, patron of the arts and sciences) in the morning and Hermes (nimble messenger of the gods) in the evening. Moreover, the Greeks did not know that they were seeing the same planet.
For a long time, astronomers could not figure out the movement of Mercury across the sky, and all because of the anomalous precession of its orbit. Newtonian mechanics was in no way suitable for explaining an overly elongated orbit: perihelion = 46 million km from the Sun, aphelion = 70 million km. Scientists of the 19th century even believed that some other planet (sometimes called Vulcan) was moving close to Mercury, which influenced its orbit. It became possible to correctly predict the motion of the planet only after the discovery by Einstein of his General Theory of Relativity.
Exploring the planet
The study of Mercury is very complicated due to its close location to the Sun; it is impossible to get high-quality images from the American Hubble telescope.
Only one interplanetary station approached the planet - Mariner 10, which made three flybys in 1974-1975. It turned out to make cartography only 45% of the planet.
Radar observations were also carried out, but these data are more of a theory than iron facts. So, a similar study showed the presence of frozen water at the north pole of Mercury (Mariner did not map this area).
Mercury - the smallest planet in, is at the closest distance from the Sun, belongs to the terrestrial planets. The mass of Mercury is about 20 times less than that of the earth, and the planet has no natural satellites. According to scientists, the planet has a frozen iron core, which occupies about half of the planet's volume, followed by a mantle, and a silicate shell on the surface.
The surface of Mercury is very reminiscent of the moon, and is densely covered with craters, most of which are of impact origin - from a collision with fragments that have remained since the formation of the solar system about 4 billion years ago. The surface of the planet 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 of 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 is 3476 km for the Moon, 4878 for Mercury. A day on Mercury is about 58 Earth days, or exactly 2/3 of a Mercury year. Another curious fact of the “lunar” similarity is connected with this - from the Earth, Mercury, like the Moon, always sees only the “front side”.
The same effect would have been if the Mercury day were exactly equal to the Mercury year, so before the beginning of the space age and observations using radar, it was believed that the period of rotation of the planet around its axis is 58 days.
Mercury moves very slowly around its axis, but it moves very quickly in orbit. On Mercury, a solar day is equal to 176 Earth days, that is, during this time, due to the addition of 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 actual properties of Mercury, they are in many ways similar to those of the moon - on the night side the temperature drops to -180 degrees Celsius, which is enough to freeze carbon dioxide and liquefy oxygen, on the daytime 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 absence 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.
In projection 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, about 912 times. It is possible to 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 the 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 the Sun moves backward for an observer on Mercury. Mercury is so close to the Sun that it is very difficult to observe it.
In mid-latitudes (including Russia), the planet is noticeable 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. At the same time, since the axis of the planet almost does not deviate from 0 degrees, even on the planet closest to the Sun (at its poles), there are craters, the bottom of which the sun's rays never reached.
2. Mercury makes one revolution around the Sun in 88 Earth days, and around its axis one revolution 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's magnetic field strength is 300 times less than the magnetic field strength of the 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 planets of the terrestrial group, 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 Venus and Mars are the closest orbits to the Earth, Mercury is 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 of a large number of 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. Almost 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. A body that hit the surface of Mercury in ancient times must have had a diameter of at least 100 km.
8. Around the sun, the planet Mercury rotates at an average speed of 47.87 km / s, which makes it the fastest planet in the solar system.
9. Mercury is the only planet in the solar system that has Joshua effect. This effect is as follows: 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 vice versa - from west to east. This is possible as a result of the fact that for about 8 days the rotational speed of Mercury is less than the orbital speed of the planet.
10. Not so long ago, thanks to mathematical modeling, scientists came up with the assumption that Mercury is not an independent planet, but a long-lost satellite of Venus. However, while there is no material evidence, this is nothing more than a theory.
A solar day on Mercury lasts 176 Earth days.. And the period of its revolution around its axis relative to the stars is exactly equal to 2/3 of a Mercurial year. With such exact relations, the rotation is called resonant. All peculiarities Mercury's movements are largely due to gravitational influence sun, including changes in the orientation of the orbit planets.
As the planet closest to the Sun, Mercury receives much more energy from the central luminary than, for example, the Earth (10 times on average). Due to the elongation of the orbit, the energy flux from the Sun varies by about a factor of two.. The long duration of day and night leads to the fact that the brightness temperatures (measured by infrared radiation in accordance with Planck's law of thermal radiation) on the "day" and on the "night" sides of the surface of Mercury at an average distance from the Sun can vary from about 600 K to 100 K. But already at a depth of several tens of centimeters there are no significant temperature fluctuations, which is a consequence of the very low thermal conductivity of the rocks.
Surface of Mercury, covered with crushed basalt-type material, rather dark. Based on observations from Earth and photographs from spacecraft, it is generally similar to the surface of the Moon, although the contrast between dark and light areas is less pronounced. Along with craters (generally less deep than on the Moon), there are hills and valleys.
Above the surface of Mercury there are traces of a very rarefied atmosphere. containing, in addition to helium, also hydrogen, carbon dioxide, carbon, oxygen and noble gases (argon, neon). The proximity of the Sun determines the tangible influence of the solar wind on Mercury. Due to this proximity, the tidal effect of the Sun on Mercury is also significant, which should lead to the appearance above the surface planets electric field, the strength of which can be about twice that of the "clear weather field" above the Earth's surface, and differs from the latter in comparative stability.
Mercury also has a magnetic field.. The magnetic dipole moment of Mercury is about four orders of magnitude less than that of the Earth; however, since the field strengths are inversely proportional to the cube of the radius of the planets, they are close in order of magnitude on Mercury and on Earth.
Several models of the internal structure of Mercury have been proposed.. According to the most common (albeit preliminary) opinion, the planet consists of a hot, gradually cooling iron-nickel core and a silicate shell, at the boundary between which the temperature can approach 103 K. The core accounts for more than half of the mass planets
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 it 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. This 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 above 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 of the rotational 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 is 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 ultrabasic rocks such as 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, having passed the entire planet and focused at the opposite point of the surface, led to the formation of a kind of rugged "chaotic" landscape here. 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 on 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 the radioactive isotopes thorium-232 and uranium-238 of the more refractory elements of uranium and thorium does not fit into the high temperatures that are 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 a magnetic field that is 100 times weaker than Earth's. Mercury's magnetic field has a dipole structure and is highly symmetrical, and its axis deviates by only 10 degrees from the planet's axis of rotation, 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 such conditions, there have recently been suggestions that ice may 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, 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 team's first image was taken in June 2006 with the US Air Force's 3.7-meter telescope at Mount Haleakala, Hawaii, and then three smaller instruments were used: one at Haleakala and two at 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.
In ancient Greece, at 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, with two corresponding to the morning appearance of Mercury, and two to the evening), which was the messenger of the underworld. In Hebrew, Mercury was called "Koch in Ham".
Mercury in the 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.
Research of Mercury with 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. An analysis was also made of the prevalence of 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 an analogue of the Roman god Mercury in the languages of different peoples of the world. 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 Tyr (ancient Armenian deity).
Mercury craters (with two exceptions) are named after famous people in the humanitarian field (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, were of correspondingly greater importance in world culture. The larger the crater, the stronger the influence of the individual on the 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.
Mercury is the smallest and closest planet to the Sun in the solar system. The ancient Romans gave him a 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 across the sky.
a brief description of
Due to its small size and proximity to the Sun, Mercury is inconvenient for terrestrial observations, so very little was known about it for a long time. An important step in its study was made thanks to the Mariner-10 and Messenger spacecraft, with the help of which high-quality images and a detailed surface map were obtained.
Mercury belongs to the terrestrial planets and is located at an average distance of about 58 million km from the Sun. The maximum distance (at aphelion) is 70 million km, and the minimum distance (at perihelion) is 46 million km. Its radius is only slightly larger than that of the Moon, at 2,439 km, and its density is almost the same as that of the Earth, at 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. The acceleration of free fall is 2.6 times less than the earth's - 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 revolves around the Sun in 88 days, and the period of rotation around its axis relative to the stars (sidereal day) is two-thirds of the period of revolution - 58 days. This means that one day on Mercury lasts two of its years, that is, 176 Earth days. The commensurability of the periods, apparently, is explained by the tidal action 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 plane of the ecliptic) - the angle between them is 7 degrees. The speed of the planet in orbit 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 the night side and poles to 700 K (430 °C) at noon at the equator. At the same time, daily temperature fluctuations rapidly decrease with advancement deep into the crust, that is, the thermal inertia of the soil is large. From this it was concluded that the soil on the surface of Mercury is the so-called regolith - a highly fragmented rock with a low density. The surface layers of the Moon, Mars and its satellites Phobos and Deimos also consist of regolith.
Planet formation
The most likely description of the origin of Mercury is the nebular hypothesis, according to which the planet was a satellite of Venus in the past, and then, for some reason, got out of the influence of its gravitational field. According to another version, Mercury was formed simultaneously with all the objects of the solar system in the inner part of the protoplanetary disk, from where the light elements were already carried by the solar wind to the outer regions.
According to one version of the origin of the very heavy inner core of Mercury - the giant collision theory - the mass of the planet was originally 2.25 times greater than the current one. However, after a collision with a small protoplanet or planet-like object, most of the crust and upper mantle dissipated into space, and the core began to make up a significant part 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, because its surface is dotted with many craters. Rapid 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 features of the relief were born: ridges, mountains, hills and ledges.
Internal structure 
The structure of Mercury as a whole differs little from the rest of the terrestrial planets: in the center there is a massive metallic core with a radius of about 1800 km, surrounded by a mantle layer of 500 - 600 km, which, in turn, is covered with a crust 100 - 300 km thick.
It was previously believed that the core of Mercury 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 a planet's own magnetic field, albeit a weak one, 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 makes up 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, light rays radiate from young craters in different directions. However, there are no such extensive seas on Mercury, which, moreover, would be relatively flat and free from craters. Another noticeable difference in the landscapes is the numerous ledges hundreds of kilometers long, formed during the compression of Mercury. 
Craters are located on the surface of the planet unevenly. Scientists suggest that areas that are more densely filled with craters are older, and more even are young. Also, the presence of large craters suggests that on Mercury for at least 3-4 billion years there have been no crustal shifts and surface erosion. The latter is evidence that a sufficiently dense atmosphere has never existed on the planet.
The largest crater on Mercury is about 1500 kilometers in size and 2 kilometers in height. Inside it is a huge lava plain - the Zhara Plain. This object is the most visible detail on the surface of the planet. The body that collided with the planet and gave rise to such a large-scale formation must have been at least 100 km long.
Pictures of the probes 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 lifted by it from the surface. One of the sources of helium and argon are radioactive decays 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, comet impacts on the surface, sublimation of ice, presumably located in craters at the poles.
Mercury has a weak magnetic field, the intensity of which at the equator is 100 times less than on Earth. However, this tension is enough to create a powerful magnetosphere around the planet. The field axis almost coincides with the rotation axis, the age is estimated at about 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, it is quite difficult to observe Mercury from Earth. It never moves more than 28 degrees from the Sun and therefore is almost invisible. The visibility of Mercury depends on the geographic latitude. It is easiest to observe it at the equator and latitudes close to it, since twilight lasts the least here. At higher latitudes, Mercury is much more difficult to see - it is very low above the horizon. Here, the best conditions for observation occur during the greatest distance of Mercury from the Sun or at the 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 from 80 mm in diameter. However, surface detail can naturally only be seen with much larger telescopes, and even with such instruments, this will be a difficult task.
Mercury has phases similar to those of the moon. At a minimum distance from the Earth, it is visible as a thin sickle. In the full phase, it is too close to the Sun, and it is impossible to see it.
When launching the Mariner-10 probe to Mercury (1974), a gravitational maneuver was used. Direct flight of the apparatus to the planet
required a huge amount of energy and was practically impossible. This difficulty was circumvented by orbit correction: first, the device passed by Venus, and the conditions for flying past it were chosen so that its gravitational field changed its trajectory just enough that the probe flew to 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 be 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 those observed. To explain this, a hypothesis was put forward that there is another invisible planet Vulcan in the orbit of Mercury, the influence of which introduces the observed inconsistencies. The real explanation was given decades later with Einstein's general theory of relativity. Subsequently, the name of the planet Vulcan was given to vulcanoids - the alleged 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.
