Mercury is the smallest and closest planet to the Sun solar system. The ancient Romans gave it its name in honor of the god of trade Mercury, the messenger of other gods who wore winged sandals, because the planet moves faster than others in the sky.

a brief description of

Due to its small size and proximity to the Sun, Mercury is inconvenient for earthly observations, so for a long time very little was known about it. An important step in its study was made thanks to the Mariner-10 and Messenger spacecraft, with the help of which high-quality images were obtained and detailed map surfaces.

Mercury is a planet terrestrial group and is located at an average distance of about 58 million km from the Sun. In this case, the maximum distance (at aphelion) is 70 million km, and the minimum (at perihelion) is 46 million km. Its radius is only slightly larger than that of the Moon - 2,439 km, and its density is almost the same as that of the Earth - 5.42 g/cm³. High density means that it contains a significant proportion of metals. The mass of the planet is 3.3 10 23 kg, and about 80% of it is the core. The acceleration of gravity is 2.6 times less than on Earth - 3.7 m/s². It is worth noting that the shape of Mercury is ideally spherical - it has zero polar compression, that is, its equatorial and polar radii are equal. Mercury has no satellites.

The planet orbits the Sun in 88 days, and the period of rotation around its axis relative to the stars (sidereal day) is two-thirds of the orbital period - 58 days. This means that one day on Mercury lasts two of its years, that is, 176 Earth days. The commensurability of the periods is apparently explained by the tidal influence of the Sun, which slowed down the rotation of Mercury, which was initially faster, until their values ​​became equal.

Mercury has the most elongated orbit (its eccentricity is 0.205). It is significantly inclined to the plane of the earth's orbit (the ecliptic plane) - the angle between them is 7 degrees. The planet's orbital speed is 48 km/s.

The temperature on Mercury was determined by its infrared radiation. It varies over a wide range from 100 K (-173 °C) at night and the poles to 700 K (430 °C) at noon at the equator. At the same time, daily temperature fluctuations quickly decrease as one moves deeper into the crust, that is, the thermal inertia of the soil is high. From this it was concluded that the soil on the surface of Mercury is the so-called regolith - highly fragmented rock with low density. The surface layers of the Moon, Mars and its satellites Phobos and Deimos also consist of regolith.

Education of the planet

The most likely description of the origin of Mercury is considered to be the nebular hypothesis, according to which the planet was in the past a satellite of Venus, and then for some reason came out of the influence of its gravitational field. According to another version, Mercury was formed simultaneously with all objects of the Solar system in the inner part of the protoplanetary disk, from where light elements were already carried by the solar wind to the outer regions.

According to one version of the origin of Mercury's very heavy inner core - the giant impact theory - the planet's mass was initially 2.25 times greater than its current one. However, after a collision with a small protoplanet or planet-like object, most of the crust and upper mantle was scattered into space, and the core began to make up a significant portion of the planet's mass. The same hypothesis is used to explain the origin of the Moon.

After the completion of the main stage of formation 4.6 billion years ago, Mercury was intensively bombarded by comets and asteroids for a long time, which is why its surface is dotted with many craters. Violent volcanic activity at the dawn of Mercury's history led to the formation of lava plains and "seas" inside the craters. As the planet gradually cooled and contracted, other relief features were born: ridges, mountains, hills and ledges.

Internal structure

The structure of Mercury as a whole differs little from the other terrestrial planets: in the center there is a massive metallic core with a radius of about 1800 km, surrounded by a layer of mantle of 500 - 600 km, which, in turn, is covered with a crust 100 - 300 km thick.

It was previously believed that Mercury's core is solid and makes up about 60% of its total mass. It was assumed that such a small planet could only have a solid core. But having your own magnetic field The planet, although weak, has a strong argument in favor of the version of its liquid core. The movement of matter inside the core causes a dynamo effect, and the strong elongation of the orbit causes a tidal effect that maintains the core in a liquid state. It is now reliably known that the core of Mercury consists of liquid iron and nickel and accounts for three-quarters of the mass of the planet.

The surface of Mercury is practically no different from the moon. The most noticeable similarity is the countless number of craters, large and small. As on the Moon, light rays radiate from young craters in different directions. However, Mercury does not have such vast seas, which would also be relatively flat and free of craters. Another noticeable difference in the landscapes is the numerous ledges hundreds of kilometers long, formed by the compression of Mercury.

Craters are located unevenly on the surface of the planet. Scientists suggest that areas more densely filled with craters are older, and smoother areas are younger. Also, the presence of large craters suggests that there have been no crustal shifts or surface erosion on Mercury for at least 3-4 billion years. The latter is proof that the planet never had a sufficiently dense atmosphere.

The largest crater on Mercury is about 1,500 kilometers in size and 2 kilometers in height. Inside it there is a huge lava plain - the Plain of Heat. This object is the most noticeable feature on the planet's surface. The body that collided with the planet and gave birth to such a large-scale formation must have been at least 100 km long.

The probes' images showed that the surface of Mercury is homogeneous and the reliefs of the hemispheres do not differ from each other. This is another difference between the planet and the Moon, as well as from Mars. The composition of the surface is noticeably different from the lunar one - it contains few of the elements that are characteristic of the Moon - aluminum and calcium - but quite a lot of sulfur.

Atmosphere and magnetic field

The atmosphere on Mercury is practically absent - it is very rarefied. Its average density is equal to the same density on Earth at an altitude of 700 km. Its exact composition has not been determined. Thanks to spectroscopic studies, it is known that the atmosphere contains a lot of helium and sodium, as well as oxygen, argon, potassium and hydrogen. Atoms of elements are brought from outer space by the solar wind or raised from the surface by it. One source of helium and argon is radioactive decay in the planet's crust. The presence of water vapor is explained by the formation of water from hydrogen and oxygen contained in the atmosphere, impacts of comets on the surface, and sublimation of ice, presumably located in craters at the poles.

Mercury has a weak magnetic field, the strength of which at the equator is 100 times less than on Earth. However, such tension is enough to create a powerful magnetosphere for the planet. The field axis almost coincides with the rotation axis; the age is estimated at approximately 3.8 billion years. The interaction of the field with the solar wind enveloping it causes vortices that occur 10 times more often than in the Earth's magnetic field.

Observation

As already mentioned, observing Mercury from Earth is quite difficult. It is never more than 28 degrees away from the Sun and is therefore practically invisible. The visibility of Mercury depends on latitude. It is easiest to observe it at the equator and latitudes close to it, since twilight lasts the shortest here. At higher latitudes, Mercury is much more difficult to see - it is very low above the horizon. Here best conditions for observation occur at the time of Mercury's greatest distance from the Sun or at its greatest height above the horizon during sunrise or sunset. It is also convenient to observe Mercury during the equinoxes, when the duration of twilight is minimal.

Mercury is fairly easy to see with binoculars just after sunset. The phases of Mercury are clearly visible in a telescope of 80 mm in diameter. However, surface details 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 the phases of the Moon. On minimum distance from the Earth it is visible as a thin sickle. In its full phase it is too close to the Sun to be seen.

When launching the Mariner 10 probe to Mercury (1974), a gravity assist maneuver was used. Direct flight of the device to the planet required enormous amounts of energy and was practically impossible. This difficulty was circumvented by correcting the orbit: first, the device passed by Venus, and the conditions for flying past it were selected so that its gravitational field changed its trajectory just enough that the probe reached Mercury without additional expenditure of energy.

There are suggestions that ice exists on the surface of Mercury. Its atmosphere contains water vapor, which may well exist in a solid state at the poles inside deep craters.

In the 19th century, astronomers observing Mercury could not find an explanation for its orbital motion using Newton's laws. The parameters they calculated differed from the observed ones. To explain this, it was hypothesized that there is another invisible planet Vulcan in the orbit of Mercury, the influence of which introduces the observed inconsistencies. The real explanation came decades later using Einstein's general theory of relativity. Subsequently, the name of the planet Vulcan was given to vulcanoids - supposed asteroids located inside the orbit of Mercury. Zone from 0.08 AU up to 0.2 a.u. gravitationally stable, so the probability of the existence of such objects is quite high.

Of all the currently known planets in the solar system, Mercury is the object of least interest to the scientific community. This is explained primarily by the fact that a small star, dimly burning in the night sky, in fact turned out to be the least suitable in terms of applied science. The first planet from the Sun is a lifeless space testing ground, where nature itself clearly trained in the process of forming the Solar System.

In fact, Mercury can be safely called a real storehouse of information for astrophysicists, from which one can glean a lot of interesting data about the laws of physics and thermodynamics. Using the information obtained about this interesting celestial object, you can get an idea of ​​the influence that our star has on the entire solar system.

What is the first planet of the solar system?

Today, Mercury is considered the smallest planet in the system. Since Pluto was excluded from the list of the main celestial bodies of our near space and transferred to the category of dwarf planets, Mercury took an honorable first place. However, this leadership did not add points. The place that Mercury occupies in the solar system leaves it out of sight of modern science. This is all due to its close location to the Sun.

This unenviable situation leaves an imprint on the behavior of the planet. Mercury at a speed of 48 km/s. rushes along its orbit, making a complete revolution around the Sun in 88 Earth days. It rotates around its own axis quite slowly - in 58,646 days, which gave astronomers a reason for a long time to consider Mercury to be turned to the Sun on one side.

With a high degree of probability, it was precisely this agility of the celestial body and its proximity to the central luminary of our solar system that became the reason to give the planet a name in honor of the ancient Roman god Mercury, who was also distinguished by his swiftness.

To the credit of the first planet of the solar system, even the ancients considered it an independent celestial body that revolves around our star. From this angle, academic data about our star’s closest neighbor is interesting.

Brief description and features of the planet

Of all the eight planets in the solar system, Mercury has the most unusual orbit. Due to the planet’s insignificant distance from the Sun, its orbit is the shortest, but its shape is a highly elongated ellipse. Compared to the orbital path of other planets, the first planet has the highest eccentricity - 0.20 e. In other words, the movement of Mercury resembles a giant cosmic swing. At perihelion, the Sun's rapid neighbor approaches it at a distance of 46 million km, becoming red-hot. At aphelion, Mercury moves away from our star to a distance of 69.8 million km, managing to cool down a little in the vastness of space during this time.

In the night sky, the planet has a luminosity over a wide range from −1.9m to 5.5m, but its observation is very limited due to Mercury's close proximity to the Sun.

This feature of orbital flight easily explains the wide range of temperature differences on the planet, which is the most significant in the Solar System. However, the main distinguishing feature of the astrophysical parameters of the small planet is the displacement of the orbit relative to the position of the Sun. This process in physics is called precession, and what causes it still remains a mystery. In the 19th century, a table of changes in the orbital characteristics of Mercury was even compiled, but it was not possible to fully explain this behavior of the celestial body. Already in the middle of the 20th century, an assumption was made about the existence of a certain planet near the Sun that influenced the position of Mercury’s orbit. Confirm this theory in this moment technical means Observations using a telescope are not possible due to the close location of the region under study to the Sun.

The most suitable explanation for this feature of the planet's orbit is to consider precession from the point of view of Einstein's theory of relativity. Previously, the orbital resonance of Mercury was estimated as 1 to 1. In fact, it turned out that this parameter has a value of 3 to 2. The axis of the planet is located at right angles to the orbital plane, and the combination of the speed of rotation of the solar neighbor around its own axis with the orbital speed leads to a curious phenomenon . The luminary, having reached the zenith, begins its reverse motion, so on Mercury the sunrise and sunset occur in one part of the Mercury horizon.

As for the physical parameters of the planet, they are as follows and look rather modest:

• the average radius of the planet Mercury is 2439.7 ± 1.0 km;
• the mass of the planet is 3.33022·1023 kg;
• Mercury's density is 5.427 g/cm³;
• the acceleration of gravity at the Mercury equator is 3.7 m/s2.

The diameter of the smallest planet is 4879 km. Among the terrestrial planets, Mercury is inferior to all three. Venus and Earth are real giants compared to small Mercury; Mars is not much larger than the size of the first planet. The solar neighbor is inferior in size even to the satellites of Jupiter and Saturn, Ganymede (5262 km) and Titan (5150 km).

Relative to the Earth, the first planet of the solar system occupies different positions. The closest distance between the two planets is 8 2 million km, while the maximum distance is 217 million km. If you fly from Earth to Mercury, the spacecraft can reach the planet faster than going to Mars or Venus. This occurs due to the fact that a small planet is often located closer to Earth than its neighbors.

Mercury has a very high density, and in this parameter it is closer to our planet, almost twice as large as Mars - 5.427 g/cm3 versus 3.91 g/cm2 for the Red Planet. However, the acceleration of gravity for both planets, Mercury and Mars, is almost the same - 3.7 m/s2. For a long time, scientists believed that the first planet of the solar system was in the past a satellite of Venus, but obtaining accurate data on the mass and density of the planet debunked this hypothesis. Mercury is a completely independent planet, formed during the formation of the Solar System.

With its modest size, only 4879 kilometers, the planet is heavier than the Moon, and in density exceeds such huge celestial bodies as the Sun, Jupiter, Saturn, Uranus and Neptune combined. However, such a high density did not provide the planet with other outstanding physical parameters, either in terms of geology or in terms of the state of the atmosphere.

Internal and external structure of Mercury

For all terrestrial planets characteristic feature is a hard surface.

This is explained by the similarity of the internal structure of these planets. In terms of geology, Mercury has three classical layers:

• Mercurian crust, the thickness of which varies in the range of 100-300 km;
• the mantle, which is 600 km thick;
• iron-nickel core with a diameter of 3500-3600 km.

Mercury's crust is like the scales of a fish, where layers of rocks formed as a result of geological activity of the planet in the early periods were layered on top of each other. These layers formed peculiar convexities, which are features of the relief. The rapid cooling of the surface layer led to the fact that the bark began to shrink like shagreen leather, losing its strength. Subsequently, with the end of the planet’s geological activity, the Mercury crust was subjected to strong external influence.

The mantle looks quite thin compared to the thickness of the crust, only 600 km. Such a small thickness of the Mercury mantle speaks in favor of the theory according to which part of the planetary substance of Mercury was lost as a result of the collision of the planet with a large celestial body.

As for the core of the planet, there are many controversial issues. The diameter of the core is ¾ of the diameter of the entire planet and is in a semi-liquid state. Moreover, in terms of the concentration of iron in the core, Mercury is the undisputed leader among the planets of the solar system. The activity of the liquid core continues to influence the surface of the planet, forming peculiar geological formations on it - swelling.

For a long time, astronomers and scientists had poor understanding of the surface of the planet, based on visual observation data. It was only in 1974, with the help of the American space probe Mariner 10, that humanity first had the opportunity to see the surface of its solar neighbor at close range. From the resulting images we were able to find out what the surface of the planet Mercury looks like. Judging by the images obtained by Mariner 10, the first planet from the Sun is covered with craters. The largest crater, Caloris, has a diameter of 1550 km. The areas between the craters are covered with Mercurian plains and rock formations. In the absence of erosion, the surface of Mercury has remained almost the same as it was at the dawn of the formation of the Solar System. This was facilitated by the early cessation of active tectonic activity on the planet. Changes in the Mercurian topography occurred only as a result of the fall of meteorites.

In its own way color scheme Mercury strongly resembles the Moon, just as gray and faceless. The albedo of both celestial bodies is also almost the same, 0.1 and 0.12, respectively.

As for the climatic conditions on the planet Mercury, it is a harsh and cruel world. Despite the fact that under the influence of a nearby star the planet heats up to 4500 C, the heat is not retained on the Mercury surface. On the shadow side of the planetary disk, the temperature drops to -1700C. The reason for such sharp temperature fluctuations is the extremely thin atmosphere of the planet. In terms of physical parameters and its density, the Mercury atmosphere resembles a vacuum, however, even in such an environment, the planet’s air layer consists of oxygen (42%), sodium and hydrogen (29% and 22%, respectively). Only 6% comes from helium. Less than 1% comes from water vapor, carbon dioxide, nitrogen and inert gases.

It is believed that the dense air layer on the surface of Mercury disappeared as a result of the planet's weak gravitational field and the constant influence of the solar wind. The close proximity of the Sun contributes to the presence of a weak magnetic field on the planet. In many ways, this proximity and the weakness of the gravitational field contributed to the fact that Mercury has no natural satellites.

Mercury Research

Before 1974, the planet was mainly observed in optical instruments. With the beginning of the space age, humanity had the opportunity to begin a more intensive study of the first planet of the solar system. Only two earthly spacecraft managed to reach the orbit of the small planet - the American Mariner 10 and Messenger. The first made a three-time flyby of the planet during 1974-75, approaching Mercury at its maximum possible distance - 320 km.

Scientists had to wait twenty long years until NASA's Messenger spacecraft set off for Mercury in 2004. Three years later, in January 2008, an automatic interplanetary station made its first flyby of the planet. In 2011, the Messenger spacecraft safely took place in the planet’s orbit and began studying it. After four years, having spent its life, the probe fell to the surface of the planet.

The number of space probes sent to explore the first planet of the solar system, in comparison with the number of automatic vehicles sent to explore Mars, is extremely small. This is due to the fact that launching ships to Mercury is difficult from a technical point of view. To get into Mercury's orbit, it is necessary to perform a lot of complex orbital maneuvers, the implementation of which requires a large supply of fuel.

In the near future, it is planned to launch two automatic space probes at once, the European and Japanese space agencies. It is planned that the first probe will explore the surface of Mercury and its interior, while the second, a Japanese spacecraft, will study the atmosphere and magnetic field of the planet.

planet Mercury

General information about the planet Mercury. Mysterious planet

Fig.1 Mercury. The image is compiled from MESSENGER photographs dated January 30, 2008. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mercury is the planet closest to the Sun and the smallest in the Solar System, both in terms of mass and diameter. In addition, Mercury has the smallest albedo. However, in terms of average density, Mercury is ahead of almost all planets, with the exception of Earth. In addition, this is one of the most mysterious planets of the solar planet, despite the fact that Mercury lies only 90 million km from Earth. It seems that the figure is quite large, but if you remember that Mars lies at the same distance from our planet - studied no worse than the Earth, then it becomes clear that there are only 2 (!) flights of spacecraft to the “nearest neighbor of the Sun” (of the known ones) - the figure is undoubtedly small and therefore it is natural that the process of studying Mercury is a very exciting activity that can captivate no less than studying any ancient manuscripts.

These are just some questions regarding the planet Mercury that still do not have an exact answer.

The first unresolved question. As mentioned above, in terms of average density, Mercury is only slightly inferior to Earth. However, in all other respects it is very similar to the Earth's natural satellite - the Moon. Such a high density of Mercury may be caused by the loss of light rocks due to some catastrophe on early stage formation. But did such a catastrophe really take place or is it just an assumption - unknown?

Question number two. There are no traces of iron found on the surface of Mercury, which is the main element in its core. What caused this is still unclear.

Another question is related to the previous one: the presence of a liquid core on Mercury. It would seem that what’s surprising about this, because the Earth’s outer core is also liquid. But the thing is that the mass of Mercury is very small (0.055 the mass of the Earth), therefore, even despite the very high temperature of its surface, reaching 400°C, its interior had to cool and harden very quickly. And in the benefit of that that Mercury still has a liquid (albeit not completely) core is evidenced both by the presence of a weak magnetic field and by the results of research by astronomers in the USA and Russia. But how this liquid core of the planet Mercury was preserved is a big question.

As can be seen from this far from complete list, the planet Mercury is full of mysteries, and any person who is interested in this can try to solve them. And to make this difficult task easier, I suggest you familiarize yourself with the information that is already known about the planet Mercury. And it’s natural to start by considering its position in the sky.

Observing the planet Mercury from Earth

Mercury is a difficult object to observe from Earth. This is due to the fact that it never visibly moves away from the Sun by more than 28.3°, i.e. has a very small angular distance - elongation. Other planets that can be observed from Earth with the naked eye are not only larger than the planet Mercury, but also lie higher above the horizon, and are visible almost every day. Mercury always has to be observed against the background of the evening or morning dawn low above the horizon, and for a very short period of time: no later than 2 hours before dawn and no later than 2 hours after sunset. However, much more often the observation time is much shorter and is only 20-30 minutes.

Fig.2 Change of phases of Mercury. Credit: website

Observing Mercury, you can notice that relative to the Sun it moves first to the right of it, then to the left, taking the form of either a narrow crescent or a small bright round spot. These visible changes associated with Mercury's reflection of sunlight are called phases and are similar to those of the Moon, with the only difference being that the size of the crescent changes noticeably over time due to changes in the distance between the Earth and Mercury.

The planet Mercury is best visible at the moments of superior conjunctions (point 5 in the figure), when it is hidden in the rays of the Sun and has a minimum diameter. At this moment, Mercury takes on the appearance of a small bright spot without any details on its surface.

Continuing its path in orbit, Mercury begins to approach the Earth and therefore the size of its disk increases. The area sanctified by the Sun begins to shrink. After some time, Mercury is no longer a round spot. And after another 36 days, only half of Mercury remains visible. The phase of the planet (i.e., the angle at the planet between the directions to the Sun and the Earth) at this moment is close to 90°.

Soon, namely after 22 days, the area sanctified by the Sun decreases even more and Mercury becomes like a thin sickle.

Fig.3 Transit of Mercury across the disk of the Sun. Image from the SOHO spacecraft and the TRACE telescope from May 7, 2003. Credit: NASA Goddard Space Flight Center

Moving further, the planet Mercury appears on the same side of the Sun as the Earth (the so-called inferior conjunction), and becomes invisible to the observer. This is due to the fact that Mercury at this moment is turned towards the Earth with its unsanctified, dark side, although the size of its disk at this moment is maximum. However, once every 3-13 years it happens that Mercury passes directly between the Sun and the Earth and becomes visible as a dim spot on the disk of the Sun.

Then the phases begin to change into reverse order: first a thin sickle appears, which begins to grow, and now half of the planet becomes visible; Another short period of time passes and Mercury is completely sanctified.

Between the appearances of the planet in the west and in the east of the Sun, from 106 to 130 days pass (on average - 116); the large difference is explained by the significant elongation of Mercury's orbit. By the way, when Mercury is clockwise ahead of the Sun (points 3-7) it is visible in the morning; when behind the Sun (points 1, 2, 8) - it is visible in the evening.

The magnitude of Mercury during observations from Earth is small and ranges from -2 to 5.5. At the same time, it is the fourth brightest planet in the sky; at its maximum brightness, when Mercury reaches -1 magnitude, it shines almost like the star Sirius, and among the planets it is second only to Venus, Mars and Jupiter.

You can see the planet Mercury with the naked eye, not to mention observations through binoculars or a telescope. But observations should be made only at a certain time of the day: this, as mentioned above, is twilight. With the help of a telescope, Mercury can be seen in the daytime, and it is practically impossible to recognize any details on it. However, observation should be carried out very carefully, because Mercury never moves far from the Sun, and if the telescope is handled ineptly, this can lead to bad consequences caused by the powerful radiation of the star closest to us.

More or less productive study of Mercury is possible only in mountain observatories or at low latitudes. This is due both to the shorter duration of twilight and to the presence of conditions suitable for observations: cleaner air than on the plains, cloudless skies, etc.

It should be noted that it was precisely on the basis of observations from Earth that it was established that: Mercury is devoid of an atmosphere (found out on the basis of the low reflectivity of Mercury, determined by the low albedo value (0.07)), the surface of its side facing the Sun is subjected to strong heating, while as the opposite shadow side cools down greatly. And with the help of the most modern telescopes, images of the planet were obtained with a resolution sufficient to examine the largest details of the Mercury surface. However, about physical properties, until recently very little was known about the nature of its rotation around its axis.

Now a lot has changed and people know almost everything about the planet Mercury. Read below about how such an amazing result was achieved...

History of exploration of the planet Mercury

The first people to observe the planet Mercury were the Sumerians from the Tigris-Euphrates region, who recorded their observations in cuneiform texts, and pastoral tribes from the Lower Nile Valley. It was 5 thousand years ago.

However, due to the complexity of observations, people for a long time thought that Mercury observed in the morning was one planet, and in the evening it was completely different.

Therefore, Mercury had two names. Thus, the Egyptians called him Set and Horus, the Indians - Buddha and Roginea, and the ancient Greeks - Apollo and Stilbon (starting from 200 BC - Hermes). In Chinese, Japanese, Vietnamese and Korean, Mercury is called the Water Star, in Hebrew - “Kohav Hama” - “ solar planet", and the inhabitants of Ancient Babylon came up with the name Nabu for Mercury, in honor of their god.

Familiar for modern man The name of the planet was given by the Romans. It was they who named Mercury Mercury, in honor of the god of travelers and traders, who among the Greeks was named Hermes. And the stylized image of the divine staff - the caduceus - served as the prototype of the astronomical sign of this planet.

By this time, people already knew that morning Mercury and evening Mercury were the same planet and were actively studying it. True, this study was reduced mainly to observations of the planet against the background of the morning or evening dawn.

The first astronomer to observe Mercury through a telescope was the great Italian astronomer Galileo Galilei. A few years later - in 1639, the Italian Giovanni Battista Zupi, when observing the first planet from the Sun, noticed that the sanctity of Mercury changes over time, i.e. There is a change of Mercury phases. This observation proved that the planet Mercury is a satellite of the Sun.

Another great astronomer of the Middle Ages, Johannes Kepler, who discovered the three laws of motion of the planets of the solar system, predicted the passage of Mercury across the disk of the Sun, which was observed by the Frenchman Pierre Gassendi on November 7, 1631.

After this event, so significant in the astronomical chronicle, there was a lull in astronomical observations for almost 250 years...

And only in late XIX centuries, astronomers again began to observe Mercury, while trying to create maps of its surface. The first such attempts were made by the Italian J. Schiaparelli and the American P. Lovell. And in 1934, the French astronomer Eugene Michel Antoniadi, when compiling his map of Mercury, proposed a system for naming dark and light surface features associated with the god Hermes. According to this system, the dark areas were called deserts (solitudo), while the light areas had their own names.

However, it should be noted that all of the maps listed above had one significant drawback: they were compiled only for one hemisphere. The reason for this was the assumption of the Italian astronomer Giovanni Schiaparelli, who, based on his astronomical observations, concluded that Mercury is constantly turned to the Sun with one side, like the Moon to the Earth..

Only in 1965, radar methods measured the exact period of the planet’s rotation around its axis, which turned out to be equal to 58.6 days. It also turned out that Mercury rotates asynchronously, making one revolution around its axis faster than one revolution around the Sun, and previously compiled maps and astronomy textbooks had to be rewritten.

It was then that the automatic interplanetary station (AMS) Mariner 10 was launched to Mercury, which, approaching the surface of the planet on March 29, 1974 at a distance of 704 km, made it possible to take a series of detailed photographs, revealing the similarity of the Mercury surface with the lunar one.

The same numerous meteorite craters (as a rule, less deep than on the Moon), hills and valleys, mountains, smooth rounded plains, which, due to their similarity to the lunar “seas,” were called basins. The largest of them, Caloris, has a diameter of 1350 km.

The difference between the surface of Mercury and the Moon was the presence of such specific relief forms as scarps - protrusions 2-3 km high that separate two areas of the surface. The scarps are believed to have formed as shear faults during the early compression of the planet.

But the most important difference between Mercury and the Moon was the presence of water, or rather water ice. Such ice is found at the bottom of craters in the polar regions of the planet. The walls of the crater protect the ice from the rays of the Sun and it never melts...

In addition to filming the surface of the AMS, a plasma shock wave and a magnetic field were detected near Mercury. It was possible to clarify the value of the planet’s radius and its mass.

A few months later, on September 21, 1974, the Mariner 10 spacecraft again flew up to Mercury. At a fairly large distance - more than 48 thousand kilometers, using temperature sensors it was found that during a day, the duration of which is 88 Earth days, the brightness temperatures of the planet's surface (measured by infrared radiation in accordance with Planck's law of thermal radiation) rise to 600K , and at night they drop to 100K (-210°C). Using a radiometer, the heat flux emitted by the surface was determined; Against the background of heated areas consisting of loose rocks, colder ones were identified, which are silicate rocks close to terrestrial basalts. This circumstance once again confirmed the similarity of the Mercury and lunar surfaces.

During its third and final flyby of Mercury, which took place on March 16, 1975 at a distance of 327 km from the surface of the planet, Mariner 10 confirmed that the magnetic field discovered a little earlier indeed belongs to the planet. Its strength is about 1/100 of the strength of the earth's magnetic field.

In addition to measuring physical fields, the station took 3 thousand photographs with a resolution of up to 50 m, which, together with photographs taken during two previous flights, covering 45% of the surface of Mercury, made it possible to compile a detailed map of its surface, although only in the western hemisphere. the eastern hemisphere remained unexplored.

Objects on the compiled map: craters, plains, ledges, received their own names. Craters - in honor of humanitarian figures: writers, poets, artists, sculptors, composers, many of whom are Russian; plains - in honor of the gods who played a role similar to the god Mercury in various mythologies, and some - after the names of the planet on different languages; the ledges are given the names of research vessels; valleys - radio observatories. Of course, there are exceptions: this is how the Northern Plain got its name from its location, and the Heat Plain - because of the high temperatures within its territory. The mountains bordering this plain bear the same name. Two more Mercury ridges are named after the astronomers Antoniadi and Schiaparelli, who compiled the first maps of this planet.

A small crater with a diameter of 1.5 km, located near the equator, was taken as a reference object for measuring longitudes in the coordinate system on the surface of Mercury. This crater is named Hun Kal, which in the language of the ancient Mayans means “twenty” (they based their counting system on this number). The 20° meridian passes through the Hun Kal crater. Longitudes on Mercury are measured from 0° to 360° west of the prime meridian.

On March 24, 1975, Mariner 10 ran out of fuel and could no longer be controlled from Earth. His mission has come to an end. But, astronomers suspect, Mariner 10 is still orbiting the Sun, sometimes passing near the planet Mercury.

Fig.5 MESSENGER. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

After the completion of the Mariner 10 mission, there were no flights to Mercury for almost thirty years. Only on August 3, 2004, from Cape Canaveral in Florida, the United States launched the Messenger spacecraft, which finally flew up to the surface of the planet on January 14, 2008. By the way, it was very difficult to do this. And here’s why: in order to move from a near-Earth orbit to a near-Mercurian orbit, it is necessary to extinguish a significant part of the Earth’s orbital speed, which is ~30 km/s, and for this it is necessary to perform a series of gravitational maneuvers. During its mission, Messenger will perform 6 such maneuvers, 5 of which have already been completed: on August 2, 2005, the device passed at an altitude of 2347 km from the Earth’s surface, on October 24, 2006, the first flight near Venus took place at a minimum altitude of 2992 km, on June 5 2007 Messenger made a second flyby of Venus, this time much lower: along the top of the clouds. 8 months later - on January 14, 2008, Messenger finally flew up to Mercury. This event was eagerly awaited not only by NASA specialists, but also by all progressive humanity. And for good reason!

Messenger took detailed images of Mercury's surface, including reverse side planet (about which we knew nothing before).

The images transmitted to Earth made it possible to establish that quite intense tectonic activity took place on the planet Mercury, traces of which, in the form of huge flat plains, are especially noticeable in the eastern hemisphere. Also during the first approach, the magnetosphere and atmosphere of Mercury were studied in more detail.

A few months later, on October 6 of the same year, Messenger again flew up to Mercury. A series of detailed photographs of the planet were taken, which revealed strange points of dark matter abundantly scattered across the surface. Astronomers believe this is the result of meteorite impacts.

In addition, as a result of the second flyby, a heterogeneous structure of the surface of Mercury was discovered, the nature of which is not completely clear, and a measurement of the Mercury landscape, which showed that the height of the measured landscape remains surprisingly constant: 30% more even than the landscape of the opposite region. No less amazing discoveries awaited astronomers under the surface of Mercury: a sharp drop in height of as much as 600 m was discovered in Mercury’s crust, which may be a “scar” left on the planet as a result of its compression during a period of rapid cooling.

On September 29, 2009, Messenger performed its final gravity assist maneuver before entering a highly elliptical polar orbit around the planet on March 18, 2011, becoming its first artificial satellite. According to the plan, after this the probe will have to work for at least two Mercury days, which is slightly less than an Earth year...

Fig.6 Global map of Mercury, compiled on the basis of images taken by Mariner 10 and Messenger. Credit: NASA

During the last flyby of the planet Mercury to date, Messenger took a number of images of hitherto unexplored areas (6% of the entire surface of the planet), conducted a study of the Mercury atmosphere and discovered traces of recent volcanic eruptions. Thus, to date, more than 98% of the surface of Mercury has been explored and photographed. The remaining 2% of the surface is polar regions, which scientists hope to explore in 2011.

Fig.7 BepiColombo. Credit: ESA

Currently, the European Space Agency (ESA), together with the Japanese Aerospace Exploration Agency (JAXA), is developing the BepiColombo mission (in honor of the scientist Giuseppe Colombo, who developed the theory of gravitational maneuver), consisting 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. In addition to studying the planet directly, both spacecraft hope to use the study area's proximity to the Sun to test general relativity.

The launch of BepiColombo is planned for 2013, and in 2019, after performing a series of gravity assist maneuvers, it will reach the orbit of Mercury, where it will split into two components. The BepiColombo mission to Mercury is expected to last approximately one Earth year.

It should be noted that the study of the planet Mercury is also carried out from Earth, using CCD radiation receivers and subsequent computer processing of images. This became possible thanks to the development of electronics and computer science.

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 on a half-meter solar telescope. Varell selected the best shots without using computer information.

Observations of Mercury were also carried out at the Abastumani Astrophysical Observatory on November 3, 2001, as well as at the Skinakas Observatory of the University of Heraklion on May 1-2, 2002. After processing the observation results using the correlation combination method, a resolved image of the planet was obtained, similar to the Mariner-10 photomosaic. This is how a map of Mercury was compiled for longitudes 210-350°.

This is where the story of Mercury exploration ends for now. But not for long. After all, already in 2011 Messenger will fly to the planet, which will probably make many more interesting discoveries. Then BepiColombo will study Mercury...

Orbital motion and rotation of the planet Mercury

Fig.8 Distance from the terrestrial planets to the Sun. Credit: Lunar and Planetary Institute

Mercury is the planet closest to the Sun. It moves around the star in a highly elongated orbit, at an average distance of 0.387 AU. (59.1 million km) At perihelion this distance decreases to 46 million km, at aphelion it increases to 69.8 million km. Thus the orbital eccentricity (e) is 0.206.

The inclination of the Mercury orbit (i) to the ecliptic plane is 7°.

In orbit, the planet Mercury not only moves, but literally flies: at a speed of about 48 km/sec, being by this indicator the fastest planet in the solar system. The entire orbital journey takes Mercury 88 days - this is the length of the Mercury year.

Unlike the crazy movement in orbit around its axis, almost perpendicularly inclined to the plane of the planetary orbit, Mercury rotates slowly, making a full revolution in 59 (58.65) Earth days, which is 2/3 of the planet’s orbital period. For several centuries, this coincidence misled astronomers, who believed that the period of Mercury's rotation around its axis and the period of its orbit around the Sun coincided. The reason for the misconception was that the most favorable conditions for observing Mercury repeat after a triple synodic period, that is, 348 Earth days, which is approximately equal to six times the period of Mercury’s rotation around its axis (352 days), so astronomers observed approximately the same area of ​​the surface planets. On the other hand, some of them believed that the Mercury day was approximately equal to the Earth's. Only in 1965 was the inconsistency of both hypotheses established, and the true time of rotation of the planet closest to the Sun was determined.

Fig.9 Arecibo Observatory. Credit: courtesy of the NAIC - Arecibo Observatory, a facility of the NSF

That year, the three-hundred-meter radio telescope at the Arecibo Observatory (Puerto Rico) sent a powerful radio pulse towards the planet Mercury. The radio pulse was reflected in a small “beam” from the central region of the planet and rushed in all directions, including to the antenna of the radar that sent it. Following the first radio pulse, a second one was sent to Mercury, which was reflected in a narrow ring around the place where the first radio pulse was reflected. And in turn there was already a third, then a fourth ring, and so on until the last one, limiting the disk of the planet (in fact, the entire process of sending a radio signal was continuous). The side of the planet farthest from the radar was in the radio shadow, and therefore nothing was reflected from it.

Because the planet rotates, the pulses reflected by each ring are not entirely uniform. The frequency at which the signal was received does not match the frequency of the sent pulse. Since in their movement around the Sun the Earth and Mercury either move away from each other or come closer, the Doppler effect occurs and the frequency shifts.

For Mercury, the largest offset of the radar signal, which operates at a wavelength of 10 cm, is 500 kHz. Also Mercury. like any other planet, it rotates, and therefore its western (left) side moves towards the impulse, causing an additional positive Doppler shift, while the eastern (right) side moves away from it and gives a negative Doppler shift. These shifts, called residual differences, at the equator near Mercury are 32 Hz.

Knowing the shifts and linear distance between the opposite edges of the planet, astronomers R. Dice and G. Pettengil, working at the Arecibo Observatory, measured the speed of Mercury’s rotation around its axis, determining it as 59 ± 5 days.

A little later, in 1971, the American scientist R. Goldstein clarified the rotation speed of Mercury. It turned out to be 58.65±0.25 days. After 3 years, the first spacecraft Mariner 10 flew to Mercury, which only corrected Goldstein’s data to 58.646 days.

Having found out the time of Mercury's rotation around its axis and the time of its rotation in orbit and comparing them, scientists were able to calculate the length of the solar day. They turned out to be equal to 176 Earth days or 2 Mercury years. During this time, the Mercury day lasts 88 earthly days and the Mercury night lasts exactly the same amount.

The synchronization of Mercury's orbit and the period of its rotation around its axis is the result of the tidal influence of the Sun. The tidal action of the Sun took away angular momentum and retarded the rotation, which was initially faster, until the two periods were related by an integer ratio. As a result, in one Mercury year, Mercury manages to rotate around its axis by one and a half revolutions. That is, if at the moment Mercury passes perihelion a certain point on its surface is facing exactly the Sun, then at the next passage of perihelion the exact opposite point on the surface will be facing the Sun, and after another Mercury year the Sun will again return to the zenith above the first point.

As a result of this movement of the planet, “hot longitudes” can be distinguished on it - two opposite meridians, which alternately face the Sun during Mercury’s passage of perihelion, and on which, because of this, an extremely high temperature is observed, even by Mercury standards - 440-500 ° C.

By the way, the Sun in the Mercury sky behaves very unusually for an earthly observer. It rises in the east, rises extremely slowly (on average one degree per twelve hours), gradually increasing in size, then reaches its highest culmination (zenith at the equator), stops, changes direction, stops again, and slowly sets. With all this doomsday, the stars would move across the sky three times faster.

Sometimes the Sun in the sky of Mercury behaves even more strangely: it rises, reaches its highest culmination, stops, and then begins to move in reverse direction, setting at the same point where it rose. After several earthly days, the Sun rises again at the same point, for a long time. This behavior of the Sun is typical for longitudes 0° and 180°. At longitudes 90° away from the “hot longitudes,” the Sun rises and sets twice. On the meridians 90° and 270° you can see three sunsets and three sunrises in one solar day, which last 176 Earth days.

The effect of the Sun's behavior in the sky of Mercury is sometimes called the Joshua effect, named after the biblical hero who can stop the movement of the Sun.

The surprising behavior of the Sun in the Mercury sky is caused by the fact that the speed of Mercury's orbital motion is constantly changing, in contrast to the speed of rotation around its axis, which is constant. Thus, in the section of the orbit near perihelion, for approximately 8 days the speed of orbital motion exceeds the speed of rotational motion.

By the way, strange as it may sound, Mercury is the closest planet to Earth most of the time.

Internal structure of the planet Mercury

Mercury is one of the densest planets in the solar system. Its average density - 5.515 g/cm 3 is only slightly inferior to the average density of the Earth, and if we keep in mind that the Earth's density is affected by stronger compression of matter due to the larger size of our planet, then it turns out that with equal sizes of planets, the density of Mercurian matter would exceed the earth's by 30%.

According to modern theory formation of planets, it is believed that in the protoplanetary dust cloud the temperature of the region adjacent to the Sun was higher than in its outer parts, which is why the lungs chemical elements carried to distant, cold parts of the cloud. As a result, in the circumsolar region where the planet Mercury is located, there is a noticeable predominance of heavy elements, the most common of which is iron.

Some scientists believe that Mercury's high density is caused by very strong solar radiation. Radiation causes the chemical reduction of oxides to their heavier, metallic form. Perhaps the Sun contributed to the evaporation and, as a result, the evaporation of the outer layer of the original Mercury crust of the planet into space, heating it to critical temperatures.

Fig. 10 Internal structure of Mercury. Credit: NASA

Affects the average density of the planet Mercury and its massive planetary core. Representing a huge ball, comparable in size to the Moon (radius 1800 km), it concentrates up to 80% of the mass of the entire planet. The average density of Mercury's core according to calculations by S.V. Kozlovskaya - 9.8 g/cm3. It is a partially molten iron-nickel substance with an admixture of sulfur, and consists of an outer liquid and an inner solid core. This assumption was put forward after the flight of the Mariner 10 probe and further radar observations of Mercury by the group of Jean-Luc Margot in 2007. Mariner discovered a weak magnetic field on the planet, and Margot's group studied variations in its rotation around its axis.

The presence of even a partially molten core on Mercury has plunged scientists into deep thought.

The fact is that, although its surface has a very high surface temperature, reaching 400 ° C, its mass is very small, and therefore the planet must have cooled and hardened very quickly. Therefore, astronomers had no doubt that such a small planet as Mercury should have a solid core. The discovery of Mariner 10 led astronomers to talk about the possibility of Mercury having at least a partially molten core, like Earth.

Thirty years after the Mariner flight, Jean-Luc Margot's group, which brought together astronomers from Cornell University (Ithaca, New York, USA) and other institutions in the United States and Russia, based on five years of radar studies of Mercury carried out using 3 ground-based radio telescopes , proved that variations associated with the rotation of Mercury are indeed characteristic of a celestial body with a molten core.

By combining all this data, physicists were able to detect periodic disruptions in Mercury's rotation caused by tidal interactions with the Sun.

The influence of the Sun, by the way, affects the rotation of the planets differently depending on their composition. This is similar to the well-known method for identifying hard-boiled eggs: a fully hardened egg rotates quickly and for a long time, while a soft-boiled egg rotates slowly and oscillates.

The results of Margot's group's measurements were published in one of the latest issues of the journal Science. The new work also adds weight to the theory that Mercury, like Earth, generates its own magnetic field through a hydromagnetic dynamo mechanism - that is, through convection of a liquid, electrically conductive metal core.

Above the core of Mercury lies a silicate shell - the mantle, 600 km thick, which is 3 times less dense than the core - 3.3 g / cm 3. At the boundary between the mantle and the core, the temperature reaches 10 3 K.

The third shell of solid Mercury is its crust, the thickness of which is 100-300 km.

Based on an analysis of photographs of Mercury, American geologists P. Schultz and D. Gault proposed a scheme for the evolution of its surface.

According to this scheme, after the process of accumulation and formation of the planet was completed, its surface was smooth.

Fig. 11 Caloris Basin on Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington. Image reproduced courtesy of Science/AAAS

Next came the process of intensive bombardment of the planet by the remnants of the preplanetary swarm, during which Caloris-type pools were formed, as well as Copernicus-type craters on the Moon. At the same time, the enrichment of the Mercury core with iron apparently occurred as a result of a collision with a large cosmic body - a planetesimal. As a result, Mercury lost up to 60% of its original mass, part of the mantle and planetary crust.

The next period was characterized by intense volcanism and the release of lava flows that filled large basins. These processes occurred as a result of the cooling of Mercury over time. The volume of the planet decreased, and its outer rocky shell - the crust, which cooled and hardened earlier than the interior, was forced to shrink. This led to cracking of the rock shell of Mercury, pushing one edge of the cracks over the other with the formation of a kind of thrusts, in which one layer of rocks is pushed over another. The upper layer, overlaid on the lower one, has a convex profile, resembling a frozen stone wave.

During this period, the so-called “spider” appeared, which is a system of more than a hundred wide grabens radiating out from a small crater in the center of the Caloris Basin. According to the hypothesis, huge masses of magma rose from the depths of Mercury to the surface of the planet, bending upward the Mercury crust.

In some places, the crust burst, and molten deep rocks poured into the resulting cracks, forming the observed grooves. But astronomers do not know how the central crater itself was formed. Apparently, it could accidentally hit the center of Caloris, or it could cause its formation, hitting hard enough to cause the crust to spring back, over such a huge area. So far, it is only clear that the Caloris basin was filled with lava approximately 3.8-3.9 billion years ago.

Approximately 3 billion years ago, the described period ended. It was replaced by a period of relative calm, when volcanic activity weakened or stopped completely (this issue is not completely clear, perhaps the Messenger AMS will be resolved), and meteorite bombardments became less frequent. This period continues to this day...

Surface of the planet Mercury

In terms of size, Mercury is the smallest planet in the solar system. Its radius is 2440 km, which is 0.38 of the Earth's radius. Surface area - 74.8 million km 2.

Fig. 12 Comparison of the planets of the solar system. Credit: website

When Mariner 10 flew past Mercury in 1974 and transmitted the images it took to Earth, astronomers were amazed: it looked so much like the Moon. The same flat plains, incl. unique - straight, numerous steep cliffs and a lifeless desert densely strewn with craters. Even the minerals scattered across the surface of the planet Mercury in the form of tiny particles are similar to those of the moon and are called silicates. But the main similarity between the Mercury and lunar surfaces lies in the presence of two main types of terrain: continents and seas.

Continents are the most ancient geological formations on the planet, covered with craters, plains, hills, mountains and canyons crossing them. Unlike the continents, the Mercurian seas are younger formations, representing vast smooth plains formed as a result of the outpouring of lavas onto the Mercurian surface and the deposition of material ejected during the formation of craters. They appear darker than the Mercury continents, but lighter than the lunar seas.

Most of the seas are within the so-called. Zhara plains (lat. “Caloris Planitia” or Caloris basin) - a giant ring structure with a diameter of 1300 km, surrounded by a mountainous range. The Zhary Plain received its name because of its location: the 180° meridian passes through it, which, together with the opposite zero meridian, is one of the so-called. “hot longitudes” - those facing the Sun during Mercury’s minimum approach to it.

It is believed that the Heat Plain was formed as a result of the collision of Mercury with a large celestial body with a diameter of at least 100 km. The impact was so strong that the seismic waves, having passed through the entire planet and focused at the opposite point of the surface, led to the formation here of a kind of rugged “chaotic” landscape, a system of numerous large hills with a diameter of about a hundred kilometers, intersected by several large rectilinear valleys, clearly formed along the lines fractures in the planet's crust.

Unlike all other areas of Mercury, there are almost no small craters, so common on objects in the Solar System, almost or completely devoid of atmosphere. The presence of impact craters on all these objects was predicted in 1947 by Soviet astronomers Vsevolod Fedynsky and Kirill Stanyukovich.

Around some of the Mercury craters, radial-concentric faults were discovered - rays dividing the Mercurian crust into separate blocks, which indicates the geological youth of the craters, and shafts of surface rocks ejected during the impact. The largest craters, with a diameter of more than 200 km, have not one, but two such shafts, and unlike the lunar ones, they are one and a half times narrower and lower due to the greater gravity of Mercury. It should be noted that the brightness of the rays emanating from the craters regularly increases towards the full moon, and then weakens again. This phenomenon is due to the fact that the bottom of small craters reflects light mainly in the same direction from which they come. Sun rays.

Fig. 13 "Spider" within the Caloris basin. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

One of the most interesting Mercury surface features is the so-called Messenger spacecraft discovered. "Spider". The Spider is located in the center of another crater - the largest Caloris basin and is a system of hundreds of grabens radiating from a small crater in the center.

Speaking of grabens. This is a purely Mercurian relief detail, representing long narrow depressions with a flat bottom. Grabens are located in the ancient continental regions of the planet and were formed during compression and cracking of the crust of Mercury during its cooling, as a result of which the surface of the planet decreased by 1% or 100 thousand km 2.

In addition to grabens, a characteristic feature of the surface of Mercury are scarps - lobe-shaped ledges, up to several tens of kilometers in diameter. The height of the scarps is up to 3 km, and the length of the largest of them can reach 500 km.

The most famous scarps are the Santa Maria Escarpment, named after the ship of Christopher Columbus, the 450 km long Antoniadi Escarpment, named after the French astronomer, and the 350 km long Discovery Escarpment, named after the ship of James Cook. It should be noted that all the ledges on Mercury are named after sea ships on which the most significant voyages in the history of mankind were made, and two are named after the astronomers Schiaparelli and Antoniadi, who made many visual observations.

Fig. 14 Craters on the surface of Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mercury craters, often large: more than 100 km. in diameter, and selectively smaller ones, are given the names of figures of world culture - famous writers, poets, artists, sculptors, composers. To designate the plains (except for the Zhara Plain and the Northern Plain), the names of the planet Mercury were used in different languages. Extended tectonic valleys were named after radio observatories that contributed to the study of planets. The names of the relief features on Mercury were given by the International Astronomical Union, an organization uniting astronomical communities around the world.

As mentioned above, the surface of Mercury is heavily cratered. There are few large craters and many of them have smaller, and therefore younger, craters on their surface. The bottom of large craters is filled with lava flows that poured onto the surface, which subsequently solidified, forming a smooth surface similar to the Mercurian seas. At the bottom of most small craters, central hills are visible, well known to astronomers from lunar landscapes.

Among the most notable Mercury craters are Beethoven - the largest on Mercury with a diameter of 625 km, Tolstoy - with a diameter of 400 km, Dostoevsky - its diameter is 390 km, Raphael, Shakespeare, Goethe, Homer and others...

By the way, comparing from photographs the environs of the North Pole of Mercury with the environs of the South Pole, astronomers noticed significant differences between them, namely the predominance of a smooth, flat surface around the North Pole, versus a heavily cratered one around the South Pole.

The atmosphere of the planet Mercury. Physical conditions on Mercury

The atmosphere of Mercury was discovered by the Mariner 10 spacecraft, thereby raising a lot of questions among astronomers, and primarily due to its existence. Mercury, being close to the Sun and having a small mass, could not have it in principle. After all, what is needed for the existence of an atmosphere?

Firstly, greater gravity: the more massive the planet and the smaller its radius, the more reliably it holds even very light gases, such as hydrogen, helium, etc. On the planet Mercury, the force of gravity is approximately three times less than on the surface of the Earth, i.e. e. it is not able to hold even gases heavier than hydrogen.

The second condition for a planet to have an atmosphere is the temperature, both of the surface and of the atmosphere itself. The energy of chaotic thermal motion of gas atoms and molecules depends on temperature. The higher it is, the higher the particle speed, therefore, having reached the limiting value, namely the second cosmic speed, gas particles leave the planets forever, and light gases are the first to escape into outer space.

On Mercury, the temperature of the surface layers can reach 420°-450°C, which is one of the record values ​​among the planets of the Solar System. At such extreme temperatures, helium is the first to “escape.” However, contrary to all the arguments listed above, helium was found in the atmosphere of Mercury. What is the reason for the presence of this gas, which in theory should have evaporated from the atmosphere of the planet closest to the Sun billions of years ago. And this is connected precisely with the position of Mercury in a certain place in outer space.

Lying in close proximity to the Sun, Mercury is constantly fed with helium, which is supplied to it by the solar wind - a stream of electrons, protons and helium nuclei flowing from the solar corona. Without this replenishment, all the helium in the Mercury atmosphere would have evaporated into outer space within 200 days.

In addition to helium, the presence of hydrogen, oxygen and sodium was discovered in the atmosphere of Mercury, but in very small quantities, as well as the presence of traces of carbon dioxide and alkali metal atoms. So the number of helium molecules in a column of “air” above 1 cm 2 of the Mercury surface is only 400 trillion, the number of molecules of other gases is an order of magnitude less. The total number of gas molecules in the column of Mercury's atmosphere is 2x10 14 over 1 cm 2 of surface area.

The small amount of gases in the planet’s atmosphere indicates its extreme rarefaction: the pressure of all Mercury gases per 1 cm 2 of the planet’s surface area of ​​half a billion is less than the pressure at the surface of the Earth. In addition, the rarefied atmosphere, as well as the low thermal conductivity of the surface layer of Mercury, is not able to equalize the temperature, which leads to its sharp daily fluctuations. So the average temperature of the day side of Mercury is 623K, and the night side is only 103K. However, at a depth of several tens of centimeters, the temperature is approximately constant and stays at around 70-90°C.

Despite extremely high daytime temperatures, the presence of water ice is allowed in the polar regions of Mercury. This conclusion was made on the basis of data from a radar study, which showed the presence of a substance that strongly reflects radio waves, which, apparently, is water ice. The existence of ice is possible only at the bottom of deep craters, where sunlight never penetrates.

Mercury's magnetic field. Magnetosphere of the planet Mercury

In 1974, the Mariner 10 spacecraft discovered that the planet Mercury has a weak magnetic field. Its strength is 100-300 times less than the strength of the Earth's magnetic field and increases as it moves toward the poles.

Fig. 15 Magnetosphere of Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mercury's magnetic field is global, has a dipole structure, is stable and symmetrical: its axis deviates by only 2° from the planet's rotation axis. In addition to the dipole, Mercury has fields with four and eight poles.

Scientists believe that Mercury's magnetic field is formed by the rotation of the substance of its liquid outer core. By the way, the rotation, or better yet, the movement of matter in the core of Mercury occurs in a very interesting way, which scientists from two American universities described in their article: Illinois and the Western Reserve Region.

To better understand the physical state in Mercury's core, scientists used a heavy-duty press to study the behavior of a mixture of iron and sulfur under conditions of high pressure and temperature. In each experiment, samples of a mixture of iron and sulfur were subjected to a certain pressure and heated to a certain temperature. The samples were then cooled, cut in half, and examined under an electron microscope and an electron microanalyzer.

Rapid cooling preserved the structure of the samples, which showed a separation into solid and liquid phases, and sulfur was contained in each of them, says the study's lead author, Illinois graduate student Bin Chen. Based on the data from our experiment, we can draw conclusions about what is happening in the core of Mercury, he adds.

As the molten mixture of iron and sulfur cools in the outer layers of the core, iron atoms condense into "snowflakes" that fall toward the center of the planet. As the cold iron "snow" sinks and the light, sulfur-rich liquid rises, convective currents create a giant dynamo that creates the planet's relatively weak magnetic field.

In addition to the magnetic field, the planet Mercury has an extensive magnetosphere, which is strongly compressed from the side of the Sun under the influence of the solar wind.

1. Mercury is the closest planet - Mercury's average distance from the Sun is 57.91 million kilometers. The distance from the Sun is 149.6 million kilometers.

2. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system. This title belongs to the neighboring one, since the carbon dioxide ocean and dense clouds of sulfuric acid create a strong greenhouse effect on its surface.

3. A year on Mercury lasts 88 Earth days - it revolves around the Sun in 88 Earth days.

4. There are areas on Mercury that the sun's rays do not illuminate. Research suggests that glaciers exist in these dark zones.

5. Sunny side The planet heats up much more than the polar regions and the side in the shadow, so the temperature on its surface ranges from −190 to +430 °C.

6. Mercury's core makes up 83% of the planet's total volume (radius ≈1800 kilometers), which is approximately equal to the size.

7. From the surface of Mercury, the Sun will appear three times larger than from Earth.

8. Mercury is the smallest planet in the solar system - its equatorial radius is only 2439.7 kilometers. (The radius of the Earth is 6378.1 kilometers).

9. The first complete map of the planet was compiled only in 2009, thanks to images from the Mariner 10 and Messenger spacecraft.

10. From the surface of the Earth, Mercury is visible for a very short period of time after the onset of morning or evening twilight.

11. The surface of this planet is heavily dotted with impact craters, since after its formation Mercury was subjected to intense bombardment by asteroids and comets.

12. The highest point on Mercury is at an altitude of 4.48 kilometers, and the lowest point is at -5.38 kilometers.

13. Mercury's craters are named after famous people in the humanitarian field of activity; the mountains take their names from the word "heat" in different languages, and the valleys on this planet are named after abandoned ancient settlements on Earth.

14. This planet got its name in honor of the ancient Roman god of trade - fast Mercury, since it moves across the celestial sphere faster than other planets.

15. The proximity of the Sun makes it difficult to observe Mercury, which is why it is the least studied terrestrial planet.

16. Due to the fact that sending a spacecraft to Mercury is extremely difficult, only two interplanetary stations have explored it. The first of them, Mariner 10, flew past the planet three times in 1974-1975. The second, Messenger, made its first flyby of Mercury in 2008.

17. The mass of Mercury is approximately 18 times less than that of Earth.

18. The most prominent feature on Mercury's surface is the Plain of Heat, whose diameter is a third of the planet's diameter, or 1,550 kilometers.

19. Although the closest orbits to Earth are Mars and Venus, Mercury is, on average, the planet closest to Earth more often than others, since Venus is also moving away from Earth to a greater extent than Mercury.

20. Mercury experiences the most dramatic temperature changes in the solar system. This occurs due to its proximity to the Sun and the extremely thin atmosphere of the planet.

What is the mass of Mercury and its distinctive features? Find out more about this...

Features of the planet

The countdown of the planets of the solar system begins with Mercury. The distance from the Sun to Mercury is 57.91 million km. This is quite close, so the temperature on the surface of the planet reaches 430 degrees.

In some characteristics, Mercury is similar to the Moon. It has no satellites, the atmosphere is very thin, and the surface is rugged with craters. The largest is 1,550 km wide from an asteroid that crashed into the planet about 4 billion years ago.

The thin atmosphere does not allow heat to be retained, so Mercury is very cold at night. The difference in night and day temperatures reaches 600 degrees and is the largest in our planetary system.

The mass of Mercury is 3.33 10 23 kg. This indicator makes the planet the lightest and smallest (after Pluto was deprived of the title of planet) in our system. Mercury's mass is 0.055 that of Earth's. By not much more The average radius is 2439.7 km.

The depths of Mercury contain a large amount of metals, which form its core. It is the second densest planet after Earth. The core makes up about 80% of Mercury.

Observations of Mercury

We know the planet under the name Mercury - this is the name of the Roman messenger god. The planet was observed back in the 14th century BC. The Sumerians called Mercury the “jumping planet” in astrological tables. It was later named after the god of writing and wisdom "Nabu".

The Greeks named the planet in honor of Hermes, calling it "Hermaon". The Chinese called it the “Morning Star”, the Indians - Budha, the Germans identified it with Odin, and the Mayans - with the owl.

Before the invention of the telescope, European researchers had difficulty observing Mercury. For example, Nicolaus Copernicus, when describing the planet, used the observations of other scientists not from northern latitudes.

The invention of the telescope made life much easier for research astronomers. Mercury was first observed from a telescope by Galileo Galilei in the 17th century. After him, the planet was observed by: Giovanni Zupi, John Bevis, Johann Schröter, Giuseppe Colombo and others.

Its close location to the Sun and infrequent appearance in the sky have always created difficulties for the study of Mercury. For example, the famous Hubble telescope cannot recognize objects so close to our star.

In the 20th century, radar methods began to be used to study the planet, which made it possible to observe the object from Earth. Spacecraft sending to the planet is not easy. This requires special manipulations, which consume a lot of fuel. In its entire history, only two ships have visited Mercury: Mariner 10 in 1975 and Messenger in 2008.

Mercury in the night sky

The apparent magnitude of the planet ranges from −1.9 m to 5.5 m, which is quite enough to see it from Earth. However, it is not easy to see due to its small angular distance relative to the Sun.

The planet is visible for a short time after dusk falls. At low latitudes and near the equator, the days last the shortest, so it is easier to see Mercury in these places. The higher the latitude, the more difficult it is to observe the planet.

In mid-latitudes, you can “catch” Mercury in the sky during the equinox, when twilight is shortest. You can see it several times a year, both in the early morning and in the evening, during periods when it is furthest away from the Sun.

Conclusion

Mercury is the most Mass of Mercury is the smallest of the planets in our system. The planet was observed long before the beginning of our era, however, to see Mercury, certain conditions are needed. Therefore, it is the least studied of all the terrestrial planets.