A planet in the solar system whose orbit is within the Earth's orbit. The fact that Mercury is close to the Sun makes it virtually invisible to the naked eye. In fact, Mercury can be observed near the Sun 2 hours after sunset and 2 hours after sunrise.

Mercury is denoted by the symbol ☿.

Despite this, Mercury has been known since at least Sumerian times, about 5,000 years ago. In classical Greece he was called Apollo when he appeared as the morning star before sunrise and was called Hermes when he appeared as the evening star just after sunset.

Until the end of the 20th century, Mercury was one of the least studied planets, and even now we can talk about insufficient information about this planet.

So, for example, the length of its day, that is, the period of a complete revolution around its axis, was not determined until 1960.

Mercury is most comparable in size and relief shape with the Moon, but

Mercury is much denser, with a metallic core that makes up about 61% of its volume (compared to 4% for the Moon and 16% for the Earth).

The surface of Mercury differs from the lunar landscape in the absence of massive dark lava flows.

The proximity of Mercury to the Sun does not allow for full-fledged studies directly from the Earth. For a more in-depth study of the planet, the United States launched a spacecraft, which was given the name Messenger ("Messenger" - as indicated in the media).

The envoy was launched in 2004, flew past the planet in 2008, in 2009, entered the orbit of Mercury in 2011.

The proximity of Mercury to the Sun is used to study the theory of how gravity affects space and time.

The main characteristics of Mercury

Mercury is the closest planet to the Sun in the solar system.

The average orbital distance is 58 million km, it has the shortest duration of the year (an orbital period of 88 days) and receives the most intense solar radiation compared to all the planets.

Mercury is the smallest planet in the solar system, with a radius of 2440 km, it is smaller than Jupiter's largest moon, Ganymede, or Saturn's largest moon, Titan.

Mercury is an unusually dense planet, its average density is about the same as that of the Earth, but it has less mass and therefore is less compressed by its own gravity, adjusted for self-compression, the density of Mercury is the highest compared to any of the planets in the solar system.

Nearly two-thirds of Mercury's mass is contained in an iron core that extends from the planet's center with a radius of about 2100, or about 85% of its volume. The rocky outer shell of the planet - its crust and mantle layer have a thickness (depth) of only 300 km.

Problems of studying the planet Mercury

Mercury from Earth is never observed more than 28° in angular distance from the Sun.

The synodic period of Mercury is 116 days. Visible proximity to the horizon means that Mercury is always visible through the more turbulent currents of the Earth's atmosphere, which blur the visible image.

Even outside the atmosphere, orbiting observatories such as the Hubble Space Telescope require special setups and highly sensitive sensors to observe Mercury.

Because Mercury's orbit is within Earth's orbit, it occasionally passes directly between the Earth and the Sun. This event, when the planet can be observed as a small black dot that crosses the bright disk of the sun, is called a transit eclipse, this happens about a dozen times a century.

Mercury also makes it difficult for space probes to study. The planet is deep in the gravitational field of the Sun, a very large amount of energy is needed to form the trajectory of the spacecraft in order to enter the orbit of Mercury from the Earth.

The first spacecraft to approach Mercury was Mariner 10, which made three short flybys around the planet in 1974-75. But it was orbiting the Sun, not Mercury.

When developing follow-up missions to Mercury by Messenger spacecraft in 2004, engineers had to calculate complex routes using gravity from repeated flybys of Venus and Mercury over several years. The point is also that thermal radiation comes not only from the Sun, but also from Mercury itself, thus, when developing spacecraft to study Mercury, it is necessary to develop a system of protection against thermal radiation.

Mercury and tests of the theory of relativity.

Mercury made it possible to conduct and once again prove the consistency of Einstein's theory of relativity. The bottom line is that mass should affect space and speed. The experiment was as follows. When the location of the Earth, Mercury and the Sun becomes such that between Mercury and the Earth is the Sun, but not in a straight line, but somewhat to the side. An electromagnetic signal is sent from Earth to Mercury, it is reflected from Mercury and comes back to Earth. Knowing the distance to Mercury at a given time and the speed of signal propagation, scientists came to the conclusion that the signal to Mercury went in curved space. The curvature of this space was influenced by the huge mass of the Sun, that is, the signal did not go along a conventional straight line, but deviated slightly towards the Sun. Thus, this was the second important confirmation of the theory of relativity.

Data from spacecraft Mariner 10, Messenger.

Mariner 10 flew close to Mercury three times, but Mariner 10 orbited the Sun? And not Mercury and its orbit partially coincided with the orbit of Mercury itself, in this regard, it was not possible to study 100% of the planet's surface, the pictures were taken on an area of ​​​​about 45% of the entire surface of the planet. Mercury was found to have a magnetic field, and scientists did not expect that such a small planet and so slowly rotating would have such a powerful magnetic field. A spectral study has shown that Mercury has a very rarefied atmosphere.

First substantial post-mission telescopic surveys of Mercury Mariner 10 led to the discovery of sodium in its atmosphere, this happened in the mid-1980s. In addition, studies from more advanced ground-based radars have led to the creation of maps of the hemisphere, invisible Mariner 10 and in particular to the discovery of condensed material in craters near the poles, possibly ice.

In 2008 research Messenger, made it possible to obtain photographs of more than 1/3 of the planet's surface. The study took place within 200 km from the planet's surface and made it possible to consider many previously unknown geological features. In 2011 Messenger entered Mercury orbit and began research.

Mercury atmosphere

The planet is very small and hot, so there is little chance for Mercury to retain its atmosphere, even if it once existed. It should be noted that the pressure on the surface of Mercury is less than one trillionth of the pressure on the surface of the Earth.

However, the traces of atmospheric components that have been found have provided clues to planetary processes.

Mariner 10 detected a small number of helium atoms and an even smaller amount of atomic hydrogen near the surface of Mercury. These atoms are mainly formed from the solar wind - the flow of charged particles from the Sun, but these substances are constantly formed and constantly go back to the outer expanses of the Solar System. Perhaps the delay of the substance occurs no longer than a few hours.

Mariner 10 also detected atomic oxygen, which, along with the sodium, potassium, and calcium subsequently detected by telescopic observations, is likely formed from the surface of Mercury's soil or from the impact of meteorites, and released into the atmosphere either by the impact or bombardment of solar wind particles.

Atmospheric gases, as a rule, accumulate on the night side of Mercury and are dispersed by the action of the Sun in the morning.

Many atoms are ionized by the solar wind and Mercury's magnetosphere. Unlike Mariner 10, the Messenger spacecraft has instruments that can detect ions. During the first flyby of the Messenger in 2008, ions of oxygen, sodium, magnesium, potassium, calcium and sulfur were detected. In addition, Mercury has a peculiar tail, which is detected when viewing sodium emission lines.

The idea that the planet closest to the Sun could have a significant amount of water ice initially seemed strange.

However, Mercury must have accumulated water over its entire history, for example from impacts from comets. Water ice on the hot surface of Mercury will immediately turn into steam, and individual water molecules will move in random directions, along a ballistic trajectory.

Calculations show that it is possible that 1 in 10 water molecules may eventually be concentrated in the polar regions of the planet.

Because Mercury's axis of rotation is essentially perpendicular to the plane of its orbit, sunlight at the poles strikes almost horizontally.

Under such conditions, the planet's poles are constantly in shadow and provide cold traps into which water molecules can fall for millions or billions of years. Gradually the polar ice will grow. But the reflected rays of the Sun, from the edges of the craters, will stop its growth, and it will be covered with dust and debris from the meteorite bombardment, let's say - garbage.

Radar data suggests that the reflective layer is indeed covered with a layer of 0.5 meters of such debris.

It is impossible to say with 100% certainty that the caps of Mercury are covered with ice or at least partially contained ice.

It can also be atomic sulfur, a very common substance in space.

Research on Mercury continues and new secrets of this planet will be revealed over time.

Mercury Features:

Weight: 03302 x10 24 kg

Volume: 6.083 x10 10 km 3

Radius: 2439.7 km

Average density: 5427 kg/m3

Gravity (ed ): 3.7 m/s

Free fall acceleration: 3.7 m/s

Second escape velocity: 4.3 km/s

Solar energy: 9126.6 W/m2

Distance from the Sun: 57.91x 10 6 km

Synodic period: 115.88 days

Maximum orbital speed: 58.98 km/s

Minimum orbital speed: 38.86 km/s

Orbital inclination: 7o

Period of rotation around its axis: 1407.6 hours

Daylength: 4226.6 hours

Tilt of the axis to the plane of the ecliptic: 0.01 o

Minimum distance to Earth: 77.3 x 10 6 km

Maximum distance to Earth: 221.9x 10 6 km

Average temperature on the illuminated side: +167 C

Average temperature on the shady side: -187 C

Dimensions of Mercury compared to Earth:

What the surface of Mercury looks like - Atmosphere and temperature on Mercury - Studying and observing Mercury - Interesting facts about Mercury

What does the surface of Mercury look like?

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, thanks 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 the projection on the celestial sphere, the planet is visible as a star-shaped object that does not depart from the Sun further than 28 degrees of arc, 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)

1. 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.

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 effect 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 scattered into space, and the core began to make up a significant part of the mass of the planet. 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 planets of the terrestrial group: 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.

Mercury occupies the first place in the list of planets of our solar system. Despite the rather modest size, this planet has an honorable role: to be closest to our star, to be approached by the cosmic body of our luminary. However, this location cannot be called very successful. Mercury is the closest planet to the Sun and is forced to endure the full force of the hot love and warmth of our star.

Astrophysical characteristics and features of the planet

Mercury is the smallest planet in the solar system, belonging together with Venus, Earth and Mars to the terrestrial planets. The average radius of the planet is only 2439 km, and the diameter of this planet at the equator is 4879 km. It should be noted that the size makes the planet not only the smallest among other planets in the solar system. In size, it is even smaller than some of the largest satellites.

Jupiter's satellite Ganymede and Saturn's satellite Titan have a diameter of over 5,000 km. Jupiter's moon Callisto is about the same size as Mercury.

The planet is named after the sly and swift Mercury, the ancient Roman god of trade. The choice of name is not accidental. A small and nimble planet moves the fastest in the sky. The movement and length of the orbital path around our star takes 88 Earth days. This speed is due to the close location of the planet to our star. The planet is at a distance from the Sun within 46-70 million km.

The following astrophysical characteristics of the planet should be added to the small size of the planet:

• the mass of the planet is 3 x 1023 kg or 5.5% of the mass of our planet;
• the density of a small planet is slightly inferior to that of the earth and equals 5.427 g/cm3;
• the gravitational force on it or the free fall acceleration is 3.7 m/s2;
• the surface area of ​​the planet is 75 million square meters. kilometers, i.e. only 10% of the earth's surface area;
• the volume of Mercury is 6.1 x 1010 km3 or 5.4% of the volume of the Earth, i.e. 18 such planets would fit in our Earth.

Mercury rotates around its own axis with a frequency of 56 Earth days, while a Mercury day lasts half an Earth year on the surface of the planet. In other words, during a Mercury day, Mercury basks in the rays of the Sun for 176 Earth days. In this situation, one side of the planet is heated to extreme temperatures, while the other side of Mercury at this time cools to a state of cosmic cold.

There are very interesting facts about the state of the orbit of Mercury and the position of the planet in relation to other celestial bodies. There is practically no change of seasons on the planet. In other words, there is a sharp transition from a hot and hot summer to a fierce cosmic winter. This is due to the fact that the planet has an axis of rotation located perpendicular to the orbital plane. As a result of this position of the planet, there are areas on its surface that the sun's rays never touch. The data obtained from the Mariner space probes confirmed that on Mercury, as well as on the Moon, suitable water was found, which, however, is in a frozen state and is located deep under the surface of the planet. At the moment, it is believed that such areas can be found in areas close to the regions of the poles.

Another interesting property that characterizes the orbital position of the planet is the discrepancy between the speed of rotation of Mercury around its own axis and the movement of the planet around the Sun. The planet has a constant frequency of revolution, while it runs around the Sun at different speeds. Near perihelion, Mercury moves faster than the angular velocity of the planet itself. This discrepancy causes an interesting astronomical phenomenon - the Sun begins to move across the Mercury sky in the opposite direction, from the West to the east.

Given the fact that Venus is considered to be the closest planet to Earth, Mercury is often much closer to our planet than the “morning star”. The planet has no satellites, so it accompanies our star in splendid isolation.

Atmosphere of Mercury: origin and current state

Despite its close position to the Sun, the surface of the planet is separated from the star by an average of 5-7 tens of millions of kilometers, but the most significant daily temperature drops are observed on it. During the day, the surface of the planet is heated to the state of a hot frying pan, the temperature of which is 427 degrees Celsius. At night, cosmic cold prevails here. The surface of the planet has a low temperature, its maximum reaches minus 200 degrees Celsius.

The reason for such extreme temperature fluctuations lies in the state of the Mercury atmosphere. It is in an extremely rarefied state, having no effect on the thermodynamic processes on the surface of the planet. Atmospheric pressure here is very low and is only 10-14 bar. The atmosphere has a very weak influence on the climatic conditions of the planet, which is determined by the orbital position in relation to the Sun.

Basically, the atmosphere of the planet consists of molecules of helium, sodium, hydrogen and oxygen. These gases were either captured by the planet's magnetic field from solar wind particles or originated from the evaporation of the Mercury surface. The rarefiedness of the atmosphere of Mercury is evidenced by the fact that its surface is clearly visible not only from the board of automatic orbital stations, but also through a modern telescope. There is no cloudiness above the planet, opening up free access to the Mercury surface for the sun's rays. Scientists believe that this state of the Mercury atmosphere is explained by the close position of the planet to our star, its astrophysical parameters.

For a long time, astronomers had no idea what color Mercury was. However, observing the planet through a telescope and looking at pictures taken from spacecraft, scientists discovered a gray and unattractive Mercury disk. This is due to the lack of an atmosphere on the planet and the rocky landscape.

The strength of the magnetic field is clearly not able to resist the influence of the gravitational force that the Sun exerts on the planet. Solar wind streams supply the planet's atmosphere with helium and hydrogen, but due to constant heating, the heated gases dissipate back into outer space.

Brief description of the structure and composition of the planet

In this state of the atmosphere, Mercury is not able to protect itself from the attack of cosmic bodies falling on the surface of the planet. There are no signs of natural erosion on the planet, the surface is more likely to be affected by cosmic processes.

Like other terrestrial planets, Mercury has its own firmament, but unlike the Earth and Mars, which are mainly composed of silicates, it is 70% metal. This explains the rather high density of the planet and its mass. In many physical parameters, Mercury is very much like our satellite. As on the Moon, the surface of the planet is a lifeless desert, devoid of a dense atmosphere and open to cosmic influence. At the same time, the crust and mantle of the planet have a thin layer, if compared with terrestrial geological parameters. The inner part of the planet is mainly represented by a heavy iron core. It has a core, which consists entirely of molten iron and occupies almost half of the entire planetary volume and ¾ of the planet's diameter. Only an insignificant mantle, only 600 km thick, represented by silicates, separates the core of the planet from the crust. The layers of the Mercurial crust have different thicknesses, which vary in the range of 100-300 km.

This explains the very high density of the planet, which is not typical for celestial bodies similar in size and origin. The presence of a molten iron core gives Mercury a magnetic field strong enough to counteract the solar wind by trapping charged plasma particles. Such a structure of the planet is uncharacteristic for most planets in the solar system, where the core accounts for 25-35% of the total planetary mass. Probably, such mercurology is caused by the peculiarities of the origin of the planet.

Scientists believe that the composition of the planet was strongly influenced by the origin of Mercury. According to one version, it is a former satellite of Venus, which subsequently lost its rotational momentum and was forced, under the influence of the Sun's gravity, to move into its own elongated orbit. According to other versions, at the stage of formation, more than 4.5 billion years ago, Mercury collided with either Venus or another planetesimal, as a result of which most of the Mercury crust was demolished and dispersed in outer space.

The third version of the origin of Mercury is based on the assumption that the planet was formed from the remnants of cosmic matter left after the formation of Venus, Earth and Mars. Heavy elements, mostly metals, formed the core of the planet. To form the outer shell of the planet, lighter elements were clearly not enough.

Judging by the photos taken from space, the time of Mercury activity is long gone. The surface of the planet is a meager landscape, on which the main decoration are craters, large and small, presented in huge numbers. The Mercury Valleys are vast areas of solidified lava, which testifies to the former volcanic activity of the planet. The crust has no tectonic plates and covers the planet's mantle in layers.

The size of the craters on Mercury is amazing. The largest and largest crater, which was called the Heat Plain, has a diameter of more than one and a half thousand kilometers. The giant caldera of the crater, whose height is 2 km, suggests that the collision of Mercury with a cosmic body of this size had the scale of a universal cataclysm.

The early cessation of volcanic activity led to a rapid cooling of the planet's surface and the formation of an undulating landscape. The cooled layers of the crust crawled onto the lower ones, forming scales, and the impacts of asteroids and the fall of large meteorites only more disfigured the face of the planet.

Spacecraft and equipment involved in the study of Mercury

For a long time, we observed cosmic bodies, asteroids, comets, satellites of the planet and stars through telescopes, not having the technical ability to study our cosmic neighborhood in more detail and in detail. We looked at our neighbors and Mercury in a completely different way, including when it became possible to launch space probes and spacecraft to distant planets. We got a completely different idea of ​​what outer space looks like, the objects of our solar system.

The bulk of scientific information about Mercury was obtained as a result of astrophysical observations. The study of the planet was carried out with the help of new powerful telescopes. Significant progress in the study of the smallest planet in the solar system was made by the flight of the American spacecraft Mariner-10. Such an opportunity appeared in November 1973, when the Atlas rocket with an astrophysical automatic probe was launched from Cape Canaveral.

The American space program "Mariner" assumed the launch of a series of automatic probes to the nearest planets, to Venus and Mars. If the first devices were mainly directed towards Venus and Mars, then the last, tenth probe, having studied Venus along the way, flew away towards Mercury. It was the flight of a small spacecraft that gave astrophysicists the necessary information about the surface of the planet, about the composition of the atmosphere and about the parameters of its orbit.

The spacecraft performed surveys of the planet from a flyby trajectory. The flight of the spacecraft was calculated in such a way that Mariner 10 could pass as many times as possible in close proximity to the planet. The first flight took place in March 1974. The device passed from the planet at a distance of 700 km, taking the first pictures of a distant planet from a close distance. During the second flyby, the distance decreased even more. The American probe swept over the surface of Mercury at an altitude of 48 km. For the third time, Mariner 10 was separated from Mercury by a distance of 327 km. As a result of the flights of the Mariner, it was possible to obtain images of the surface of the planet and draw up an approximate map of it. The planet turned out to be seemingly dead, inhospitable and unsuitable for existing and known to science life forms.

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It belongs to the cosmic bodies of the terrestrial group and is located relatively close to us. However, comparatively little is known about Mercury today. Some time ago, it was considered the least explored planet. Various parameters (the nature of the surface, climate features, the presence of an atmosphere, its composition) of Mercury remained a mystery due to the extremely inconvenient position of the planet for observation and research using spacecraft. The reason for this is the proximity to the Sun, which spoils any equipment directed towards it or approaching it. Nevertheless, over the centuries of constant attempts at observation, impressive material was collected, which was then supplemented by data from interplanetary stations. The atmosphere of Mercury is included in the list of characteristics that were studied by Mariner 10 and Messenger. The thin air shell of the planet, like everything on it, is subject to the constant influence of the luminary. The sun is the main factor determining and shaping the features of Mercury's atmosphere.

Earth observation

It is inconvenient to admire Mercury from the surface of our planet because of its proximity to the Sun and the peculiarities of its orbit. It appears in the sky close enough to the horizon. And always during sunset or dawn. The observation time is negligible. Under the most favorable set of circumstances, this is about two hours before dawn and the same amount after sunset. In most cases, the duration of observation does not exceed 20-30 minutes.

Phases

Mercury has the same phases as the Moon. Flying around the Sun, it either turns into a narrow crescent, or becomes a full circle. In all its glory, the planet is visible when it is opposite the Earth, behind the Sun. At this time, for the observer comes the "full moon" of Mercury. At the same time, however, the planet is at its maximum distance from the Earth, and bright sunlight interferes with observation.

Moving around the star, Mercury begins to visually increase in size, as it approaches us. At the same time, the illuminated surface area is reduced. In the end, the planet turns to us with its dark side and disappears from visibility. Once every few years at such a moment, Mercury passes exactly between the Sun and the Earth. Then you can observe its movement across the disk of the star.

Observation methods

Mercury can be seen with the naked eye or observed through binoculars shortly before dawn and after sunset, that is, at dusk. With the help of a small amateur telescope, it will be possible to notice the planet during the day, but it will not be possible to see any details. It is important during such observations - do not forget about safety. Mercury never moves significantly away from the Sun, which means that both eyes and equipment must be protected from its rays.

The ideal place for observing the planet closest to the star is mountain observatories and low latitudes. Here, the astronomer comes to the aid of clean air, a cloudless sky, and a short duration of twilight.

It was earthly observations that helped establish the fact that Mercury has no atmosphere. Powerful telescopes made it possible to consider many features of the planet's surface topography and calculate the approximate difference in temperature on the illuminated and dark sides. However, only the flights of AMS (automatic interplanetary stations) were able to shed light on other characteristics of the planet and clarify the data already obtained.

"Mariner-10"

In the entire history of astronautics, only two vehicles have been sent to Mercury. The reason is a complex and expensive maneuver, which is necessary for the station to enter the orbit of the planet. Mariner 10 was the first to go to Mercury. In 1974-1975, he circled the planet closest to the Sun three times. The minimum distance that separated the apparatus and Mercury was 320 km. Mariner 10 transmitted several thousand images of the planet's surface to Earth. About 45% of Mercury was photographed. Mariner 10 measured the surface temperature on the illuminated and dark sides, as well as the planet's magnetic field. In addition, the apparatus found that the atmosphere of Mercury is practically absent, it is replaced by a thin air shell, which contains helium.

"Messenger"

The second AMS sent to Mercury was Messenger. It started in August 2004. He transmitted to Earth an image of that part of the surface that Mariner 10 did not capture, measured the landscape of the planet, looked into its craters and found spots of an incomprehensible dark substance (possibly marks from meteorite impacts), which is often found here. The apparatus studied the magnetosphere of Mercury, its gas envelope.

Messenger completed its mission in 2015. He fell on Mercury, leaving a crater 15 meters deep on the surface.

Is there an atmosphere on Mercury?

If you carefully reread the previous text, you can see a slight contradiction. On the one hand, ground-based observations testified to the absence of any kind of gas envelope. On the other hand, the Mariner-10 apparatus transmitted to Earth information, according to which the atmosphere of the planet Mercury still exists and contains helium. In the scientific community, this message also caused surprise. And it's not that it contradicted previous observations. It's just that Mercury does not have the characteristics that contribute to the formation of a gaseous envelope.

This is a mixture of gases, volatile substances, which can only be held at the surface by gravity of a certain magnitude. Small by cosmic standards, Mercury cannot boast of such a characteristic. on its surface is three times less than on Earth. Thus, the planet is not able to hold not only helium and hydrogen, but also heavier gases. And yet it was helium that was discovered by Mariner 10.

Temperature

There is another factor that casts doubt on the presence of an atmosphere of Mercury. This is the surface temperature of the planet. Mercury is the champion in this regard. During daylight hours, the temperature on the surface sometimes reaches 420-450 ºС. At such high values, the molecules and atoms of the gas begin to move faster and faster and gradually reach the second cosmic velocity, that is, nothing can hold them near the surface. In the temperature conditions of Mercury, the same helium should be the first to “escape”. In theory, it should not be on the planet closest to the Sun at all, and almost from the moment of its formation.

Special position

And yet the answer to the question of whether there is an atmosphere on Mercury is positive, although it is somewhat different from what is usually hidden behind this astronomical concept. The reason for such a fantastic and at the same time quite real state of affairs lies in the unique proximity of the star determines many of the characteristics of this cosmic body, and the atmosphere of Mercury is no exception.

The gas envelope of the planet is constantly exposed to the so-called solar wind. It originates in the corona of the star and is a stream of nuclei, protons and electrons of helium. With the solar wind, fresh portions of volatile matter are delivered to Mercury. Without such a recharge, all helium would disappear from the surface of the planet in about two hundred days.

Atmosphere of Mercury: composition

Careful research helped to discover other elements that make up the gaseous shell of the planet. Mercury's atmosphere also contains hydrogen, oxygen, potassium, calcium, and sodium. The percentage of these elements is very small. In addition, the atmosphere of the planet Mercury is characterized by the presence of traces of carbon dioxide.

The air envelope is very rarefied. The gas molecules in it actually do not interact with each other, but only move along the surface without collisions and collisions. Scientists have been able to establish the factors that determine the presence of the atmosphere of Mercury. Hydrogen, like helium, is delivered to its surface by the solar wind. The source of other elements is the planet itself or meteorites falling on it. The atmosphere of Mercury, the composition of which is planned to be thoroughly studied in the near future, is presumably formed as a result of the evaporation of rocks under the influence of the solar wind or diffusion from the bowels of the planet. Most likely, each of these factors contributes.

So, what is the atmosphere of Mercury? Highly rarefied, consisting of helium, hydrogen, traces of alkali metals and carbon dioxide. Often in the scientific literature it is called the exosphere, which only emphasizes the strong difference between this shell and a similar formation, for example, on Earth.

Despite all the difficulties, the planet Mercury is still on the list of space research targets. The atmosphere and surface of this cosmic body will probably be studied more than once using various devices. Mercury still holds a lot of interesting and unknown things. In addition, the study of such planets as Venus, Mars or Mercury, whether they are devoid of an atmosphere or not, sheds light on the history of the formation and development of the Earth.