Mercury planet diameter in km. The atmosphere of Mercury. Brief description of the structure and composition of the planet

Although the laurels of the smallest planet went to Mercury quite recently, because previously it was considered the smallest planet, but after it was demoted from the status of “full-fledged” planets, the primacy passed to Mercury, about which our article today is about.

History of the discovery of the planet Mercury

The history of Mercury and our knowledge of this planet goes back to ancient times; in fact, it is one of the first planets known to mankind. This is how Mercury was observed back in ancient Sumer, one of the first developed civilizations on Earth. The Sumerians associated Mercury with the local god of writing, Nabu. Babylonian and ancient Egyptian priests, who were also excellent astronomers of the ancient world, also knew about this planet.

As for the origin of the name of the planet “Mercury,” it comes from the Romans, who named this planet in honor of the ancient god Mercury (in the Greek version, Hermes), the patron of trade, crafts and the messenger of other Olympian gods. Also, astronomers of the past sometimes poetically called Mercury the morning or evening dawn, according to the time of its appearance in the starry firmament.

God Mercury, after whom the planet was named.

Also, ancient astronomers believed that Mercury and its closest neighbor, the planet Venus, revolved around the Sun, and not around the Earth. But in turn it revolves around the Earth.

Features of the planet Mercury

Perhaps the most interesting feature of this small planet is the fact that it is on Mercury that the largest temperature fluctuations occur: since Mercury is closest to the Sun, during the day its surface warms up to 450 C. But on the other hand, Mercury does not have its own atmosphere and cannot retain heat, as a result, at night the temperature drops to minus 170 C, here is the largest temperature difference in our solar system.

Mercury is only slightly larger in size than our Moon. Its surface is also similar to that of the Moon, riddled with craters and traces of small asteroids and meteorites.

Interesting fact: approximately 4 billion years ago, a huge asteroid crashed into Mercury, the force of which can be compared to the explosion of a trillion megaton bombs. This impact left a giant crater on the surface of Mercury, approximately the size of the modern state of Texas; astronomers called it the crater Basin Caloris.

Also very interesting is the fact that on Mercury there is real ice, which is hidden in the depths of the craters there. Ice could have been brought to Mercury by meteorites, or even formed from water vapor that escaped from the bowels of the planet.

Another interesting feature of this planet is the reduction in its size. The decrease itself, scientists believe, is caused by the gradual cooling of the planet, which occurs over millions of years. As a result of cooling, its surface collapses and lobe-shaped rocks form.

The density of Mercury is high, higher only than that of our Earth; in the center of the planet there is a huge core, accounting for 75% of the diameter of the entire planet.

With the help of NASA's Mariner 10 research probe sent to the surface of Mercury, an amazing discovery was made - there is a magnetic field on Mercury. This was all the more surprising, since according to the astrophysical data of this planet: the rotation speed and the presence of a molten core, there should be no magnetic field there. Despite the fact that the strength of Mercury's magnetic field is only 1% of the strength of the Earth's magnetic field, it is superactive - the magnetic field of the solar wind periodically enters the field of Mercury and from interaction with it strong magnetic tornadoes arise, sometimes reaching the surface of the planet.

The speed of the planet Mercury, at which it revolves around the Sun, is 180,000 km per hour. Mercury's orbit is oval-shaped and highly elongated epileptically, as a result of which it either approaches the Sun by 47 million kilometers, or moves away by 70 million kilometers. If we could observe the Sun from the surface of Mercury, it would appear three times larger from there than from Earth.

One year on Mercury is equal to 88 Earth days.

Mercury photo

We bring to your attention a photo of this planet.

Temperature on Mercury

What is the temperature on Mercury? Although this planet is located closest to the Sun, the championship of the warmest planet in the solar system belongs to its neighbor Venus, whose thick atmosphere, which literally envelops the planet, allows it to retain heat. As for Mercury, due to the lack of an atmosphere, its heat evaporates and the planet both quickly heats up and cools down quickly; every day and every night there are simply huge temperature changes from +450 C during the day to -170 C at night. At the same time, the average temperature on Mercury will be 140 C, but this is not cold, not hot, the weather on Mercury leaves much to be desired.

Is there life on Mercury?

As you probably guessed, with such temperature fluctuations the existence of life is not possible.

Atmosphere of Mercury

We wrote above that there is no atmosphere on Mercury, although one can argue with this statement; the atmosphere of the planet Mercury is not absent, it is simply different and different from what we actually understand by atmosphere.

The original atmosphere of this planet was dissipated 4.6 billion years ago due to the very weak Mercury, which simply could not contain it. In addition, the proximity to the Sun and constant solar winds also did not contribute to the preservation of the atmosphere in the classical sense of the term. However, a weak atmosphere on Mercury remains, and it is the most unstable and insignificant atmosphere in the solar system.

The composition of Mercury's atmosphere includes helium, potassium, sodium, and water vapor. In addition, the planet's current atmosphere is periodically replenished from various sources, such as solar wind particles, volcanic degassing, and radioactive decay of elements.

Also, despite its small size and scanty density, the atmosphere of Mercury can be divided into four sections: the lower, middle and upper layers, as well as the exosphere. The lower atmosphere contains a lot of dust, which gives Mercury a peculiar red-brown appearance; it warms up to high temperatures due to the heat that is reflected from the surface. The middle atmosphere has a current similar to the earth's. Mercury's upper atmosphere actively interacts with solar winds, which also heat it to high temperatures.

The surface of the planet Mercury is bare rock of volcanic origin. Billions of years ago, molten lava cooled and formed a rocky, gray surface. This surface is also responsible for the color of Mercury - dark gray, although due to the dust in the lower layers of the atmosphere it seems that Mercury is red-brown. Images of the surface of Mercury taken from the Messenger research probe are very reminiscent of the lunar landscape, the only thing is that there are no “lunar seas” on Mercury, while there are no Mercury scarps on the Moon.

Rings of Mercury

Does Mercury have rings? After all, many planets solar system, for example, and of course they are present. Alas, Mercury literally has no rings at all. Rings cannot exist on Mercury again due to the proximity of this planet to the Sun, because the rings of other planets are formed from ice debris, pieces of asteroids and other celestial objects, which near Mercury are simply melted by hot solar winds.

Moons of Mercury

Just like Mercury has no satellite rings. This is due to the fact that there are not many asteroids flying around this planet - potential candidates for satellites when they come into contact with the planet’s gravity.

Rotation of Mercury

The rotation of the planet Mercury is very unusual, namely, the orbital period of its rotation is shorter compared to the duration of rotation around its axis. This duration is less than 180 Earth days. While the orbital period is half as long. In other words, Mercury goes through two orbits in three of its revolutions.

How long does it take to fly to Mercury?

At its closest point, the minimum distance from Earth to Mercury is 77.3 million kilometers. How long will it take modern spacecraft to cover such a distance? NASA's fastest spacecraft to date, New Horizons, which was launched to Pluto, has a speed of about 80,000 kilometers per hour. It would take him about 40 days to get to Mercury, which is comparatively not that long.

The first spacecraft, Mariner 10, launched to Mercury back in 1973, was not so fast; it took 147 days to reach this planet. Technology is improving, and perhaps in the near future it will be possible to fly to Mercury in a few hours.

• Mercury is quite difficult to spot in the sky, as it “loves to play hide and seek,” literally “hiding” behind the Sun. However, ancient astronomers knew about it. This is explained by the fact that in those distant times the sky was darker due to the lack of light pollution, and the planet was visible much better.
• The shift in Mercury's orbit helped confirm Albert Einstein's famous. In short, it talks about how the light of a star changes when another planet orbits it. Astronomers reflected a radar signal from Mercury, and the path of this signal coincided with predictions general theory relativity.
• The magnetic field of Mercury, the very existence of which is very mysterious, in addition to everything else, also differs at the poles of the planet. At the south pole it is more intense than at the north.

This article is a message or report about the planet Mercury, which outlines characteristic of this planet: parameters, description of the atmosphere, surface, orbit, as well as Interesting Facts.

The planet Mercury, named after the Roman god of trade, who also acted as the messenger of the gods, is located closest to the center of the solar system than any other. This planet, located at a distance (on average) of 58 million km from the Sun, is very hot.

Parameters and description

Maximum distance from the Sun 70 million km
Minimum distance from the Sun 46 million km
Equator diameter 4878 km
Average surface temperature 350º C
Maximum temperature 430º C
Minimum temperature-170º C
Time to revolve around the Sun 88 earth days
Length of sunny day 176 earth days

On both sides of Mercury there are areas near the equator that are illuminated by the Sun most of the time. These two regions are called Mercury's "heat poles." During the Mercury day, the temperature changes very significantly. During the day, the surface of the planet warms up to an average of 350º C, sometimes up to 430º C. At this temperature, tin and lead melt. At night, the surface layers cool down to -170º C.

The main reason for such sharp temperature fluctuations is that Mercury, unlike Earth, is practically devoid of an atmosphere that absorbs heat during the day and does not allow the planet to cool down at night.

For a long time, astronomers believed that Mercury had no atmosphere at all, but now it is known that this planet still has a gaseous envelope, albeit an extremely rarefied one. For the most part it consists of sodium and helium with small amounts of hydrogen and oxygen (see Figure 1).

Rice. 1. Atmosphere of Mercury

Due to the high temperature and low pressure, liquid water cannot exist on Mercury. However, as on Earth, water here is found in the form of ice at the poles. In some polar regions of the planet, where the Sun never looks, the temperature can constantly be around -148º C.

Thus, organic life on Mercury is impossible.

Surface of the planet

These cataclysms apparently greatly heated Mercury, and when the meteorite bombardment ended, the planet began to cool and shrink. The compression led to the appearance of folds and long winding cliffs on the surface, called scarps. In some places their height can reach 3 km.

Like Earth, Mercury's relatively thin crust covers a thick layer of mantle surrounding a large, heavy iron-containing core. The average density of Mercury is extremely high. This suggests that the planet's core, relative to the rest of it, is very large and heavy. Astronomers say that Mercury's core makes up about 42% of its volume, while Earth's core makes up only 17%.

Elliptical orbit

Mercury orbits the Sun in 88 Earth days, faster than any other planet in the Solar System. Like the other planets, Mercury revolves around the Sun not in a circular orbit, but in an elongated or elliptical one.

Since the Sun is not in the center of this orbit, the distance between it and Mercury at different points varies greatly. The point at which Mercury is closest to the Sun is called perihelion, and the point at which Mercury is farthest from the Sun is aphelion.

Since the plane of Mercury's orbit is noticeably inclined relative to the Earth's orbit, it rarely, no more than a dozen times a century, passes between our planet and the Sun.

Mercury rotates not only around the Sun, but also around its own axis. This happens extremely slowly - one day on Mercury lasts 176 Earth days. As Mercury approaches perihelion, something very unusual happens. Since the planet’s motion accelerates as it approaches the Sun, the speed of Mercury’s movement along its orbit in a given segment exceeds the speed of the planet’s rotation around its axis. If you were on Mercury at such a time, you would see how the Sun, rising in the east, would cross the sky and set in the west, then reappear above the horizon, move across the sky in the opposite direction for a couple of earthly days, and then again it's gone.

Mercury is best seen at aphelion, when it is farthest from the Sun. This happens about 3 times a year.

Most of the information we have about Mercury has been obtained through radar and space probes. In addition, the Mariner 10 spacecraft, launched by the United States in the mid-1970s, repeatedly approached Mercury, transmitting images of its surface to Earth.

On August 3, 2004, the Messenger probe was launched from Cape Canaveral, which is still operating in orbit of the smallest planet in the solar system.

Some interesting facts

• Despite its maximum proximity to the Sun, Mercury is not the hottest planet in the solar system, giving way to Venus.

• Mercury has no satellites.

The idea that Mercury was once a satellite of Venus has now become widespread.

This hypothesis was born in late XIX V. The hypothesis was not taken seriously until the first spacecraft flights to Mercury revealed a number of features of its internal structure that are difficult to explain by the assumption that Mercury was formed in its orbit, like other planets. Moreover, accurate calculations of the process of planet formation led to the conclusion that Mercury could not have formed where it is now at all. The corresponding calculations were carried out and assumptions were made that Mercury was formed as a satellite of Venus in an orbit with a semi-major axis of about 400,000 km (the semi-major axis of the Moon’s orbit is 385,000 km). The large mass of Mercury caused significantly greater tidal effects than in the Earth-Moon system. This ensured a rapid slowdown in the rotation of both Venus and Mercury and rapid heating of their interiors. The tidal influence of the Earth on the Venus-Mercury system has led, in particular, to the fact that when Venus is in inferior conjunction (i.e., between the Sun and Earth), it is always turned to the Earth with the same side . This leads to an increase in the total energy of the Venus-Mercury system and its disintegration. Mercury becomes an independent planet.

The orbit of Mercury (like Pluto) differs from the orbits of other planets by its large inclination to the ecliptic and large excentricity.

Mercury's orbit is highly elongated (Fig. 47), so at perihelion (the shortest distance from the Sun) the planet moves much faster than at aphelion (the greatest distance from the Sun). This leads to a wonderful effect. At longitudes 0° and 180°, three sunrises and three sunsets can be observed within one day. True, this only happens when Mercury passes perihelion and only at the indicated longitudes.

Mercury is the planet closest to the Sun (its distance from the Sun is 2.5 times less than from the Earth), which determines the unique physical conditions on its surface. In appearance it is very similar to the Moon (Fig. 48). Its surface is also dotted with craters, there is a sea, and other relief forms characteristic of the Moon are observed. At the midday point, i.e. where the Sun is at its zenith, the temperature reaches 750 K (450 °C), and by midnight it drops to 80-90 K (-180 °C). Even more intense bombardment of the surface, due to the proximity to the Sun, determines the similarity of the lunar and Mercury regoliths. Mercury, like the Moon, has no atmosphere due to its low mass. Material from the site

Calculations show that neither the Moon nor Mercury could have maintained an atmosphere. Nevertheless, Mercury has an atmosphere! True, it is not at all similar to earthly. First of all, it is extremely sparse. Her blood pressure is 5. 10 11 times less than on the Earth's surface. Mercury's atmosphere is like a flowing river. It is continuously replenished by capturing atoms of the solar wind and is continuously dissipated. On average, each helium atom remains near the surface of Mercury for 200 days. The number of atoms in the entire atmosphere per 1 cm 2 of the planet’s surface is no more than 4. 10 14 (on Earth - 10 25) helium atoms and 30 times less hydrogen atoms. Modern technology is not capable of achieving such a vacuum.

Mercury occupies the first place in the list of planets in our solar system. Despite its rather modest size, this planet has an honorable role: to be closest to our star, to be the closest 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 ardent love and warmth of our star.

Astrophysical characteristics and features of the planet

Mercury is the smallest planet in the solar system, classified together with Venus, Earth and Mars as 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. It is even smaller in size than some of the largest satellites.

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

The planet is named after the crafty and swift Mercury, the ancient Roman god who patronized trade. The choice of name is not accidental. A small and nimble planet moves faster than anyone else 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.

To the small size of the planet, the following astrophysical characteristics of the planet should be added:

• the mass of the planet is 3 x 1023 kg or 5.5% of the mass of our planet;
• the density of the small planet is slightly lower than that of Earth and is equal to 5.427 g/cm3;
• force of gravity on it or acceleration free fall 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;
• Mercury's volume is 6.1 x 1010 km3 or 5.4% of the Earth's volume, i.e. 18 such planets would fit on 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 heats up to extreme temperatures, while the other side of Mercury cools down to a state of cosmic cold.

There are very interesting facts about the state of Mercury's orbit 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 hot and hot summer to fierce cosmic winter. This is explained by 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 on the Moon, usable water was discovered, which, however, remains 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 polar regions.

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

Considering 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.

The 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 changes are observed on it. During the day, the surface of the planet heats up to the state of a hot frying pan, the temperature of which is 427 degrees Celsius. At night, cosmic cold reigns here. The surface of the planet has low temperature, its maximum reaches minus 200 degrees Celsius.

The reason for such extreme temperature changes lies in the state of the Mercury atmosphere. It is in an extremely rarefied state, without having any effect on the thermodynamic processes on the surface of the planet. Atmosphere pressure there is very little here and is only 10-14 bar. The atmosphere has a very weak influence on the planet's climate, which is determined by its orbital position relative to the Sun.

The planet's atmosphere mainly 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 resulted from the evaporation of Mercury's surface. The rarefied nature of Mercury's atmosphere is evidenced by the fact that its surface is clearly visible not only from automatic orbital stations, but also through a modern telescope. There is no cloudiness over the planet, allowing the sun's rays free access to the Mercury surface. Scientists believe that this state of the Mercury atmosphere is explained by the close position of the planet to our star and 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 images obtained from spacecraft, scientists discovered a gray and unattractive Mercury disk. This is due to the planet's lack of atmosphere and rocky landscape.

The strength of the magnetic field is clearly unable to resist the influence of the gravitational force that the Sun exerts on the planet. Streams of solar wind supply the planet's atmosphere with helium and hydrogen, but due to constant heating, the heating gases dissipate back into outer space.

Brief description of the structure and composition of the planet

In this state of the atmosphere, Mercury is unable to protect itself from the attack of cosmic bodies falling onto the surface of the planet. There are no traces of natural erosion on the planet; the surface is more likely affected by cosmic processes.

Like other terrestrial planets, Mercury has its own solid surface, but unlike Earth and Mars, which are mainly composed of silicates, it is 70% metallic. This explains the rather high density of the planet and its mass. In many physical parameters, Mercury is very similar to 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 planet’s crust and mantle have a thin layer, if compared with terrestrial geological parameters. The interior of the planet is mainly represented by a heavy iron core. It has a core that consists entirely of molten iron and occupies almost half of the entire planetary volume and ¾ of the diameter of the planet. Only a thin mantle, only 600 km thick, represented by silicates, separates the planet's core from the crust. The layers of the Mercurian 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 planets of similar size and origin. celestial bodies. The presence of a molten iron core gives Mercury a magnetic field strong enough to counteract the solar wind, trapping charged plasma particles. This structure of the planet is uncharacteristic of most planets in the solar system, where the core accounts for 25-35% of the total planetary mass. This mercurology is probably 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 angular momentum and was forced, under the influence of the Sun’s gravity, to move to 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 scattered 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 planet's core. There were clearly not enough lighter elements to form the outer shell of the planet.

Judging by photos taken from space, the time of Mercury activity has long passed. The surface of the planet is a sparse landscape, on which the main decoration is craters, large and small, presented in huge numbers. The Mercurian valleys are vast areas of solidified lava, which testifies to the planet's past volcanic activity. The crust does not have 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 is called the Plain of Heat, 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 was on the scale of a universal cataclysm.

The early cessation of volcanic activity led to the 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 further disfigured the face of the planet.

Spacecraft and equipment involved in the exploration of Mercury

For a long time, we observed cosmic bodies, asteroids, comets, planetary satellites and stars through telescopes, without the technical ability to study our cosmic neighborhood in more detail and detail. We looked at our neighbors and Mercury in a completely different way when the opportunity arose to launch space probes and devices to distant planets. We got a completely different idea of ​​what outer space, the objects of our solar system, looks like.

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

American space program Mariner envisioned launching a series of automatic probes to the nearest planets, 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 towards Mercury. It was the flight of the small spacecraft that gave astrophysicists the necessary information about the surface of the planet, the composition of the atmosphere and the parameters of its orbit.

The spacecraft surveyed the planet from its flyby trajectory. The flight of the spacecraft was designed in such a way that Mariner 10 was able to pass in close proximity to the planet as many times as possible. The first flight took place in March 1974. The device passed from the planet at a distance of 700 km, taking the first close-up images of the distant planet. During the second flight, the distance decreased even further. 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 Mariner flights, it was possible to obtain photographs of the planet’s surface and draw up an approximate map of it. The planet turned out to be seemingly dead, inhospitable and unsuitable for existing forms of life known to science.

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The surface of Mercury, in short, resembles the Moon. Vast plains and many craters indicate that geological activity on the planet ceased billions of years ago.

Surface character

The surface of Mercury (photo shown later in the article), taken by the Mariner 10 and Messenger probes, looked similar in appearance to the Moon. The planet is largely dotted with craters of various sizes. The smallest ones visible in the most detailed photographs of Mariner measure several hundred meters in diameter. The space between large craters is relatively flat and consists of plains. It is similar to the surface of the Moon, but takes up much more space. Similar areas surround Mercury's most prominent impact structure, the Caloris Planitia basin. Only half of it was illuminated when Mariner 10 encountered it, but it was fully discovered by Messenger during its first flyby of the planet in January 2008.

Craters

The most common landforms on the planet are craters. They largely cover the surface (photos below) at first glance similar to the Moon, but upon closer examination they reveal interesting differences.

Mercury's gravity is more than twice that of the Moon, partly due to the density of its huge core of iron and sulfur. The strong force of gravity tends to keep the material ejected from the crater close to the collision site. Compared to the Moon, it fell at a distance of only 65% ​​of the lunar distance. This may be one of the factors that contributed to the appearance of secondary craters on the planet, formed under the influence of ejected material, in contrast to the primary ones, which arose directly from a collision with an asteroid or comet. Higher gravity means that the complex shapes and structures found in large craters—central peaks, steep slopes, and flat bases—are seen in smaller craters on Mercury (minimum diameter of about 10 km) than on the Moon (about 19 km). Structures smaller than these sizes have simple bowl-like outlines. Mercury's craters are different from those on Mars, although the two planets have comparable gravity. Fresh craters on the first are, as a rule, deeper than comparable formations on the second. This may be a consequence of the low volatile content of Mercury's crust or higher impact velocities (as the speed of an object in solar orbit increases as it approaches the Sun).

Craters larger than 100 km in diameter begin to approach the oval shape characteristic of such large formations. These structures - polycyclic basins - have dimensions of 300 km or more and are the result of the most powerful collisions. Several dozen of them were discovered on the photographed part of the planet. Messenger images and laser altimetry have made major contributions to understanding these residual scars from early asteroid bombardments on Mercury.

Plain of Heat

This impact structure extends over 1550 km. When it was initially discovered by Mariner 10, it was thought to be much smaller. The interior of the object consists of smooth plains covered with folded and broken concentric circles. The largest ridges extend several hundred kilometers in length, about 3 km in width and less than 300 meters in height. More than 200 fractures, comparable in size at the edges, emanate from the center of the plain; many of them are depressions bounded by grooves (grabens). Where grabens intersect with ridges, they tend to pass through them, indicating their later formation.

Surface types

The Zhary Plain is surrounded by two types of terrain - its edge and the relief formed by discarded rock. The edge is a ring of irregular mountain blocks reaching 3 km in height, which are the highest mountains found on the planet, with relatively steep slopes towards the center. The second, much smaller ring is located 100-150 km from the first. Beyond the outer slopes is a zone of linear radial ridges and valleys, partially filled with plains, some of which are dotted with numerous mounds and hills several hundred meters high. The origin of the formations that make up the wide rings around the Zhara basin is controversial. Some plains on the Moon were formed largely by the interaction of ejecta with pre-existing surface topography, and this may also be true for Mercury. But the Messenger results suggest that volcanic activity played a significant role in their formation. Not only are there few craters there compared to the Zhara basin, indicating a protracted period of plain formation, but they have other features more clearly associated with volcanism than could be seen in the Mariner 10 images. Crucial evidence of volcanism came from Messenger images showing volcanic vents, many of which lie along the outer edge of the Zhara Plain.

Raditladi Crater

Caloris is one of the youngest large polycyclic plains, at least on the explored part of Mercury. It probably formed at the same time as the last giant structure on the Moon - about 3.9 billion years ago. Messenger images revealed another, much smaller impact crater with a visible inner ring that may have formed much later, called the Raditladi Basin.

Strange antipode

On the other side of the planet, exactly 180° opposite the Plain of Heat, is a patch of strangely distorted terrain. Scientists interpret this fact by talking about their simultaneous formation by focusing seismic waves from events that affected the antipodal surface of Mercury. The hilly and line-dotted terrain is a vast area of ​​uplands, which are hilly polygons 5-10 km wide and up to 1.5 km high. Pre-existing craters were transformed into hills and cracks by seismic processes, as a result of which this relief was formed. Some of them had a flat bottom, but then its shape changed, indicating their later filling.

Plains

A plain is the relatively flat or gently undulating surface of Mercury, Venus, Earth and Mars and is found throughout these planets. It represents the “canvas” on which the landscape developed. The plains are evidence of the process of destruction of rough terrain and the creation of smoothed space.

There are at least three methods of “grinding” that probably smoothed the surface of Mercury.

One way - increasing temperature - reduces the strength of the bark and its ability to hold high relief. Over millions of years, the mountains will “sink”, the bottom of the craters will rise and the surface of Mercury will level out.

The second method involves moving rocks towards lower areas of the area under the influence of gravity. Over time, rock accumulates in low-lying areas and fills higher levels as its volume increases. This is how lava flows from the bowels of the planet behave.

The third method is for rock fragments to fall onto the surface of Mercury from above, which ultimately leads to the leveling of rough terrain. Examples of this mechanism include rock emissions from cratering and volcanic ash.

Volcanic activity

Some evidence favoring the hypothesis of the influence of volcanic activity on the formation of many of the plains surrounding the Zhara basin has already been given. Other relatively young plains on Mercury, especially visible in regions illuminated at low angles during MESSENGER's first flyby, exhibit signature volcanic features. For example, several old craters were filled to the brim with lava flows, similar to similar formations on the Moon and Mars. However, widespread plains on Mercury are more difficult to assess. Because they are older, it is clear that volcanoes and other volcanic features may have eroded or otherwise collapsed, making them difficult to explain. Understanding these old plains is important because they are likely responsible for the disappearance of most of the 10-30 km diameter craters compared to the Moon.

Scarps

The most important landforms of Mercury that provide insight into the planet's internal structure are the hundreds of jagged scarps. The length of these rocks varies from tens to more than thousands of kilometers, and their heights range from 100 m to 3 km. When viewed from above, their edges appear rounded or jagged. It is clear that this is the result of cracking, when part of the soil rose and lay on the surrounding area. On Earth, such structures are limited in volume and arise during local horizontal compression in earth's crust. But the entire explored surface of Mercury is covered with scarps, which means that the planet’s crust has shrunk in the past. From the number and geometry of scarps it follows that the planet has decreased in diameter by 3 km.

Moreover, shrinkage must have continued until relatively recent in geological history, as some scarps have altered the shape of well-preserved (and therefore relatively young) impact craters. The slowing down of the planet's initially high rotation rate by tidal forces produced compression in Mercury's equatorial latitudes. The globally distributed scars, however, suggest another explanation: late cooling of the mantle, perhaps combined with the solidification of part of the once completely molten core, led to compression of the core and deformation of the cold crust. The contraction of Mercury's size as its mantle cooled should have resulted in more longitudinal structures than can be seen, indicating that the contraction process was not complete.

The surface of Mercury: what is it made of?

Scientists have tried to figure out the composition of the planet by studying sunlight reflected from different parts of it. One of the differences between Mercury and the Moon, besides the former being slightly darker, is that it has a smaller spectrum of surface brightnesses. For example, the seas of Earth's moon—smooth expanses visible to the naked eye as large dark spots—are much darker than the cratered highlands, and the plains of Mercury are only slightly darker. The color differences on the planet are less pronounced, although Messenger images taken using a set of color filters showed small, very colorful areas associated with volcanic vents. These features, along with the relatively featureless visible and near-infrared spectrum of reflected sunlight, suggest that Mercury's surface is composed of iron- and titanium-poor silicate minerals that are darker in color compared to the lunar maria. In particular, the planet's rocks may be low in iron oxides (FeO), leading to speculation that it was formed under much more reducing conditions (i.e., lack of oxygen) than other members of the terrestrial group.

Problems of remote research

It is very difficult to determine the planet's composition by remotely sensing sunlight and the thermal spectrum that Mercury's surface reflects. The planet is heating up greatly, which changes the optical properties of mineral particles and complicates direct interpretation. However, Messenger was equipped with several instruments not present on Mariner 10 that measured chemical and mineral composition directly. These instruments required a long observation period while the craft remained near Mercury, so no concrete results were available after the first three short flybys. Only during the Messenger orbital mission did enough new information about the composition of the planet's surface.