Solar system Mercury. Planet Mercury is closest to the Sun

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

Mercury is an inner planet because its orbit lies inside the Earth's orbit. After Pluto was deprived of its planetary status in 2006, Mercury acquired the title of the smallest planet in the solar system. Mercury's apparent magnitude ranges from 1.9 to 5.5, but it is not easily visible due to its small angular distance from the Sun (maximum 28.3°). Relatively little is known about the planet yet. It was only in 2009 that scientists compiled the first complete map of Mercury, using images from Mariner 10 and Messenger. The presence of any natural satellites on the planet has not been detected.

Mercury is the smallest terrestrial planet. Its radius is only 2439.7 ± 1.0 km, which is less than the radius of Jupiter's moon Ganymede and Saturn's moon Titan. The mass of the planet is 3.3·1023 kg. The average density of Mercury is quite high - 5.43 g/cm3, which is only slightly less than the density of Earth. Considering that the Earth is larger in size, the density value of Mercury indicates an increased content of metals in its depths. Acceleration free fall on Mercury it is 3.70 m/s. The second escape velocity is 4.25 km/s. Despite its smaller radius, Mercury still exceeds in mass the satellites of the giant planets such as Ganymede and Titan.

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

Planet movement

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

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

It turned out that a Mercury sidereal day is equal to 58.65 Earth days, that is, 2/3 of a Mercury year. Such commensurability of the periods of rotation around the axis and revolution of Mercury around the Sun is a unique phenomenon for the Solar System. It is presumably explained by the fact that 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, exactly the 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, a solar day on Mercury lasts two Mercury years or three Mercury sidereal days.

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 which, because of this, are especially hot even by Mercury standards.

There are no seasons on Mercury like on Earth. This occurs because the planet's rotation axis is at right angles to the orbital plane. As a consequence, there are areas near the poles to which Sun rays never arrive. A survey carried out by the Arecibo radio telescope suggests that there are glaciers in this icy and dark zone. The glacial layer can reach 2 m and is covered with a layer of dust.

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

It is also interesting that, although the closest orbits to Earth are Mars and Venus, Mercury is often the closest planet to Earth (since the others move away more, not being so “tied” to the Sun).

Anomalous orbital precession

Mercury is close to the Sun, so the effects of general relativity are manifested in its motion to the greatest extent among all the planets in the Solar System. Already in 1859, the French mathematician and astronomer Urbain Le Verrier reported that there was a slow precession in the orbit of Mercury that could not be fully explained by calculating the influence of the known planets according to Newtonian mechanics. The precession of Mercury's perihelion is 5600 arcseconds per century. Calculation of the influence of all other celestial bodies on Mercury according to Newtonian mechanics gives a precession of 5557 arcseconds per century. Trying to explain the observed effect, he suggested that there was another planet (or perhaps a belt of small asteroids) whose orbit was closer to the Sun than Mercury, and which was introducing a disturbing influence (other explanations considered the unaccounted for polar compression of the Sun). Thanks to previously achieved successes in the search for Neptune, taking into account its influence on the orbit of Uranus, this hypothesis became popular, and the desired hypothetical planet even received the name Vulcan. However, this planet was never discovered.

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

Hypotheses for the formation of Mercury

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

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

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

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

Surface

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

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

During research conducted by the Messenger probe, over 80% of the surface of Mercury was photographed and found to be homogeneous. In this way, Mercury is not similar to the Moon or Mars, in which one hemisphere is sharply different from the other.

The first data from a study of the elemental composition of the surface using the X-ray fluorescence spectrometer of the Messenger spacecraft showed that it is poor in aluminum and calcium compared to the plagioclase feldspar characteristic of the continental regions of the Moon. At the same time, the surface of Mercury is relatively poor in titanium and iron and rich in magnesium, occupying an intermediate position between typical basalts and ultramafic rocks such as terrestrial komatiites. Sulfur was also found to be relatively abundant, suggesting reducing conditions for planet formation.

Craters

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

One of the most noticeable features of the surface of Mercury is the Plain of Heat (Latin: Caloris Planitia). This relief feature received this name because it is located near one of the “hot longitudes.” Its diameter is about 1550 km.

Probably, the body whose impact formed the crater had 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 on the surface, led to the formation of a kind of rugged “chaotic” landscape here. The force of the impact is also evidenced by the fact that it caused the ejection of lava, which formed high concentric circles at a distance of 2 km around the crater.

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

Until recently, it was assumed that in the depths of Mercury there is a metallic core with a radius of 1800-1900 km, containing 60% of the planet’s mass, since the Mariner 10 spacecraft discovered a weak magnetic field, and it was believed that a planet with such a small size cannot have liquid kernels. But in 2007, Jean-Luc Margot's group summed up the results of five years of radar observations of Mercury, during which variations in the planet's rotation were noticed that were too large for a model with a solid core. Therefore, today we can say with a high degree of confidence that the planet’s core is liquid.

The percentage of iron in Mercury's core is higher than that of any other planet in the solar system. Several theories have been proposed to explain this fact. According to the most widely supported theory in the scientific community, Mercury originally had the same ratio of metal to silicates as a normal meteorite, having a mass 2.25 times greater than now. However, at the beginning of the history of the Solar System, a planet-like body with 6 times less mass and several hundred kilometers in diameter hit Mercury. As a result of the impact, much of the original crust and mantle was separated from the planet, causing the relative proportion of the core in the planet's composition to increase. A similar process, known as the giant impact theory, has been proposed to explain the formation of the Moon. However, the first data from a study of the elemental composition of the surface of Mercury using the AMS Messenger gamma spectrometer does not confirm this theory: the abundance of the radioactive isotope potassium-40 of the moderately volatile chemical element potassium compared to the radioactive isotopes thorium-232 and uranium-238 of the more refractory elements uranium and thorium does not cope with the high temperatures inevitable during a collision. It is therefore assumed that the elemental composition of Mercury corresponds to the primary elemental composition of the material from which it formed, similar to enstatite chondrites and anhydrous cometary particles, although the iron content of enstatite chondrites examined to date is not sufficient to explain the high average density of Mercury.

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

Geological history

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

After the formation of Mercury 4.6 billion years ago, the planet was intensively bombarded by asteroids and comets. The last major bombardment of the planet occurred 3.8 billion years ago. Some regions, for example, the Plain of Heat, were also formed due to their filling with lava. This led to the formation of smooth planes inside the craters, similar to those on the Moon.

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

A magnetic field

Mercury has a magnetic field whose strength is 100 times less than that of Earth. Mercury's magnetic field has a dipole structure and is highly symmetrical, and its axis deviates only 10 degrees from the planet's rotation axis, which imposes a significant limitation on the range of theories explaining its origin. Mercury's magnetic field may be generated by a dynamo effect, much like on Earth. This effect is the result of the circulation of the planet's liquid core. Due to the pronounced eccentricity of the planet, an extremely strong tidal effect occurs. It supports the kernel liquid state, which is necessary for the dynamo effect to manifest itself.

Mercury's magnetic field is strong enough to change the direction of the solar wind around the planet, creating a magnetosphere. The planet's magnetosphere, although small enough to fit inside the Earth, is powerful enough to trap plasma from the solar wind. Observations obtained by Mariner 10 detected low-energy plasma in the magnetosphere on the night side of the planet. Explosions of active particles were discovered in the magnetotail, indicating the dynamic qualities of the planet's magnetosphere.

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

Conditions on Mercury

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

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

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

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

Hydrogen and helium likely enter the planet via the solar wind, diffuse into its magnetosphere, and then escape back into space. Radioactive decay of elements in Mercury's crust is another source of helium, sodium and potassium. Water vapor is present, released as a result of a number of processes, such as comet impacts on the surface of the planet, the formation of water from hydrogen in the solar wind and oxygen from rocks, and sublimation from ice that is found in permanently shadowed polar craters. The discovery of a significant number of water-related ions, such as O+, OH+ H2O+, was a surprise.

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

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

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

Features of observation from Earth

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

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

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

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

There is a hypothesis that the name “Apollo” corresponded to visibility in the morning sky, and “Hermes” (“Hermaon”) in the evening sky. The Romans named the planet after the fleet-footed god of commerce, Mercury, who is equivalent to the Greek god Hermes for moving through the sky faster than the other planets. The Roman astronomer Claudius Ptolemy, who lived in Egypt, wrote about the possibility of a planet moving across the disk of the Sun in his work “Hypotheses about the Planets.” He suggested that such a transit had never been observed because a planet like Mercury was too small to observe or because the moment of transit occurred infrequently.

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

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

In the Indian astronomical treatise "Surya-siddhanta", dating back to the 5th century, the radius of Mercury was estimated at 2420 km. The error compared to the true radius (2439.7 km) is less than 1%. However, this estimate was based on an imprecise assumption of the planet's angular diameter, which was taken to be 3 arcminutes.

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

Medieval observations of Mercury in the northern parts of Europe were hampered by the fact that the planet is always observed at dawn - morning or evening - against the background of a twilight sky and quite low above the horizon (especially in northern latitudes). The period of its best visibility (elongation) occurs several times a year (lasting about 10 days). Even during these periods, it is not easy to see Mercury with the naked eye (a relatively dim star against a fairly light background of the sky). There is a story that Nicolaus Copernicus, who observed astronomical objects in the northern latitudes and foggy climate of the Baltic states, regretted that he had never seen Mercury in his entire life. This legend arose based on the fact that Copernicus’s work “On the Rotations of the Celestial Spheres” does not provide a single example of observations of Mercury, but he described the planet using the results of observations of other astronomers. As he himself said, Mercury can still be “caught” from northern latitudes by showing patience and cunning. Consequently, Copernicus could well have observed Mercury and observed it, but he described the planet based on other people’s research results.

Observations using telescopes

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

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

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

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

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

Research of Mercury using modern methods

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

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

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

Mariner 10 is the first spacecraft to reach Mercury.

The European Space Agency (ESA), together with the Japanese Aerospace Exploration Agency (JAXA), is developing the Bepi Colombo mission, consisting of two spacecraft: the Mercury Planetary Orbiter (MPO) and the 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. BepiColombo is scheduled to launch in 2013, and in 2019 it will enter orbit around Mercury, where it will split into two components.

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

On March 17, 2011, the interplanetary probe Messenger entered Mercury orbit. It is assumed that with the help of equipment installed on it, the probe will be able to explore the landscape of the planet, the composition of its atmosphere and surface; Messenger's equipment also allows for research into energetic particles and plasma. The service life of the probe is determined to be one year.

On June 17, 2011, it became known that, according to the first studies conducted by the Messenger spacecraft, the planet’s magnetic field is not symmetrical relative to the poles; Thus, different numbers of solar wind particles reach Mercury's north and south poles. An analysis of the prevalence of chemical elements on the planet was also carried out.

Features of the nomenclature

The rules for naming geological objects located on the surface of Mercury were approved at the XV General Assembly of the International Astronomical Union in 1973:
The small crater Hun Kal (indicated by an arrow), serving as a reference point for Mercury's system of longitudes. Photo by AMS Mariner 10

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

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

Currently (after Pluto was demoted to dwarf planets) Mercury is the smallest of the eight planets in our solar system. Also, the planet is at the closest distance from the Sun, and therefore rotates around our star much faster than the other planets. Apparently, it was precisely the latter quality that served as the reason to name it in honor of the fastest-footed messenger of the Gods named Mercury, an extraordinary character from the legends and myths of Ancient Rome, possessing phenomenal speed.

By the way, it was the ancient Greek and Roman astronomers who more than once called Mercury both the “morning” and “evening” star, although for the most part they knew that both names correspond to the same cosmic object. Even then, the ancient Greek scientist Heraclitus pointed out that Mercury and Venus rotate around the Sun, and not around.

Mercury today

Today, scientists know that due to Mercury's close proximity to the Sun, temperatures on its surface can reach up to 450 degrees Celsius. But the lack of an atmosphere on this planet does not allow Mercury to retain heat and on the shadow side the surface temperature can drop sharply to 170 degrees Celsius. The maximum temperature difference between daytime and nighttime on Mercury turned out to be the highest in the Solar System - more than 600 degrees Celsius.

Mercury is slightly larger in size than the Moon, but much heavier than ours. natural satellite.

Despite the fact that the planet has been known to people since time immemorial, the first image of Mercury was obtained only in 1974, when the Mariner 10 spacecraft transmitted the first images in which it was possible to make out some features of the relief. After this, a long-term active phase began to study this cosmic body, and several decades later, in March 2011, a spacecraft called Messenger reached the orbit of Mercury. after which, finally, humanity received answers to many questions.

The atmosphere of Mercury is so thin that it practically does not exist, and the volume is about 10 to the fifteenth power less than the dense layers of the Earth's atmosphere. Moreover, the vacuum in the atmosphere of this planet is much closer to a true vacuum if we compare it with any other vacuum created on Earth using technical means.

There are two explanations for the lack of atmosphere on Mercury. Firstly, this is the density of the planet. It is believed that with a density of only 38% of the Earth's density, Mercury is simply not able to retain much of the atmosphere. Secondly, the proximity of Mercury to the Sun. Such a close distance to our star makes the planet most susceptible to the influence of solar winds, which remove the last remnants of what can be called an atmosphere.

However, no matter how scarce the atmosphere on this planet is, it still exists. According to the NASA space agency, its chemical composition consists of 42% oxygen (O2), 29% sodium, 22% hydrogen (H2), 6% helium, 0.5% potassium. The remaining insignificant part consists of molecules of argon, carbon dioxide, water, nitrogen, xenon, krypton, neon, calcium (Ca, Ca +) and magnesium.

It is believed that the rarefaction of the atmosphere is due to the presence of extreme temperatures on the surface of the planet. The most low temperature can be on the order of -180 °C, and the highest is approximately 430 °C. As mentioned above, Mercury has the largest range of surface temperatures of any planet in the Solar System. The extreme maxima present on the side facing the Sun are precisely the result of an insufficient atmospheric layer that is not able to absorb solar radiation. By the way, the extreme cold on the shadow side of the planet is due to the same thing. The lack of a significant atmosphere prevents the planet from holding solar radiation and the heat very quickly leaves the surface, freely escaping into outer space.

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

But in 1974, after a magnificent three-time flyby of the surface of Mercury by the Mariner 10 spacecraft, the first fairly clear photographs of the surface were obtained. Surprisingly, despite significant time constraints, the Mariner 10 mission photographed almost half of the entire surface of the planet. As a result of analyzing observational data, scientists were able to identify three significant features of the surface of Mercury.

The first feature is the huge number of impact craters that gradually formed on the surface over billions of years. The so-called Caloris basin is the largest of the craters, with a diameter of 1,550 km.

The second feature is the presence of plains between the craters. These smooth surface areas are believed to have been created by the movement of lava flows across the planet in the past.

And finally, the third feature is the rocks, scattered across the entire surface and reaching from several tens to several thousand kilometers in length and from one hundred meters to two kilometers in height.

Scientists especially emphasize the contradiction of the first two features. The presence of lava fields indicates that there was once active volcanic activity in the planet's historical past. However, the number and age of craters, on the contrary, indicate that Mercury was geologically passive for a very long time.

But the third distinctive feature of Mercury's surface is no less interesting. It turned out that the hills are formed by the activity of the planet’s core, which results in the so-called “bulging” of the crust. Similar bulges on Earth are usually associated with the displacement of tectonic plates, while the loss of stability of Mercury's crust occurs due to the contraction of its core, which is gradually compressed. The processes occurring at the core of the planet lead to compression of the planet itself. Recent calculations by scientists indicate that the diameter of Mercury has decreased by more than 1.5 kilometers.

Structure of Mercury

Mercury is made up of three distinct layers: the crust, the mantle, and the core. The average thickness of the planet's crust, according to various estimates, ranges from 100 to 300 kilometers. The presence of the previously mentioned bulges on the surface, whose shape resembles those of the earth, indicates that, despite being sufficiently hard, the crust itself is very fragile.

The approximate thickness of Mercury's mantle is about 600 kilometers, which suggests that it is relatively thin. Scientists believe that it was not always so thin and that in the past there was a collision of the planet with a huge planetesmial, which led to the loss of significant mass of the mantle.

The core of Mercury has become the subject of much research. It is believed to be 3,600 kilometers in diameter and has some unique properties. The most interesting property is its density. Considering that the planetary diameter of Mercury is 4878 kilometers (it is smaller than the satellite Titan, whose diameter is 5125 kilometers, and the satellite Ganymede with a diameter of 5270 kilometers), the density of the planet itself is 5540 kg/m3 with a mass of 3.3 x 1023 kilograms.

So far, there is only one theory that has attempted to explain this feature of the planet's core, and has cast doubt on whether Mercury's core is actually solid. Having measured the characteristics of the bounce of radio waves from the surface of the planet, a group of planetary scientists came to the conclusion that the planet’s core is actually liquid and this explains a lot.

Mercury's orbit and rotation

Mercury is much closer to the Sun than any other planet in our system and, accordingly, it requires the shortest time to orbit. A year on Mercury is only about 88 Earth days.

An important feature of Mercury's orbit is its high eccentricity compared to other planets. Additionally, of all the planetary orbits, Mercury's orbit is the least circular.
This eccentricity, along with the lack of a significant atmosphere, explains why Mercury's surface experiences the widest range of temperature extremes in the Solar System. Simply put, Mercury's surface heats up much more when the planet is at perihelion than at aphelion, because the difference in distance between these points is too great.

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

Despite the fact that Newtonian mechanics (i.e. classical physics) predicts the rates of this precession in great detail, the exact values ​​have never been determined. This became a real problem for astronomers in the late nineteenth and early twentieth centuries. Many concepts have been formulated to explain the differences between theoretical interpretations and actual observations. According to one theory, it was even suggested that there is an unknown planet whose orbit is closer to the Sun than that of Mercury.

However, the most plausible explanation was found after Einstein's general theory of relativity was published. Based on this theory, scientists were finally able to describe the orbital precession of Mercury with sufficient accuracy.

Thus, for a long time it was believed that Mercury's spin-orbit resonance (the number of revolutions in its orbit) was 1:1, but it was eventually proven that it was actually 3:2. It is thanks to this resonance that a phenomenon is possible on the planet that is impossible on Earth. If an observer were on Mercury, he would be able to see the Sun rising to its very high point in the sky, and then “turns on” the reverse stroke and descends in the same direction from which it rose.

1. Mercury has been known to mankind since ancient times. Although the exact date of its discovery is unknown, the first mention of the planet is believed to have appeared around 3000 BC. among the Sumerians.
2. A year on Mercury is 88 Earth days long, but a Mercury day is 176 Earth days long. Mercury is almost completely blocked by tidal forces from the Sun, but over time the planet slowly rotates around its axis.
3. Mercury orbits the Sun so quickly that some early civilizations believed it was actually two different stars, one of which appears in the morning, and the other in the evening.
4. With a diameter of 4.879 km, Mercury is the smallest planet in the solar system and is also one of the five planets that can be seen in the night sky with the naked eye.
5. After Earth, Mercury is the second densest planet in the solar system. Despite small sizes, Mercury is very dense as it is composed mainly of heavy metals and rock. This allows us to classify it as a terrestrial planet.
6. Astronomers did not realize that Mercury was a planet until 1543, when Copernicus created a heliocentric model of the solar system, in which the planets revolve around the sun.
7. The gravitational forces of the planet are 38% of the gravitational forces of the Earth. This means that Mercury is unable to retain the atmosphere it has, and what remains is blown away by the solar wind. However, these same solar winds attract gas particles and dust from micrometeorites to Mercury and form radioactive decay, which in some way forms an atmosphere.
8. Mercury has no moons or rings due to its low gravity and lack of atmosphere.
9. There was a theory that between the orbits of Mercury and the Sun there was an undiscovered planet Vulcan, but its presence was never proven.
10. Mercury's orbit is an ellipse, not a circle. It has the most eccentric orbit in the solar system.
11. Mercury has only the second highest temperature among the planets in the solar system. The first place is taken

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 distinctive feature The astrophysical parameters of a 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. It is not possible to confirm this theory at the moment with technical means of observation using a telescope, 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 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

Until 1974, the planet was mainly observed with 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.

Space is a unique world in which not only cold, darkness and vacuum reign, but life is in full swing there far beyond the invisible horizon, new planets are born, young asteroids and comets appear. Today we know different Interesting Facts about the planet Mercury and the solar system, their diversity, uniqueness and pristine beauty.

1. Mercury is considered the smallest planet in our solar system, its dimensions practically do not exceed the size of the Moon. The diameter of Mercury's equator is 4879 kilometers.
2. Mercury is the only planet in the solar system that does not have its own satellites.

   

3. At certain points on the surface of Mercury, you can observe how at sunrise the Sun rises low above the horizon, after which it sets back and rises again. The same phenomenon occurs during sunset. This phenomenon is explained by the elliptical shape of Mercury's orbit and its leisurely rotation around its own axis.

   

4. Mercury makes a complete revolution around the Sun in 88 Earth days. In order to turn around its axis, Mercury requires 58.65 Earth days, this number of days is 2/3 of a year on a distant planet.

   

5. Mercury is the only planet in the solar system where sudden temperature changes are observed.. On the side of the planet, which is illuminated by the Sun, the air temperature reaches up to +430 degrees Celsius, while at the same time its opposite side is shrouded in night, and the air temperature can exceed -180 degrees Celsius. Therefore, the opinion that Mercury is the hottest planet is incorrect.

   

6. Mercury is characterized by such a phenomenon as the Joshua effect. The sun in the sky of this planet begins to move in a different direction, that is, the opposite, from west to east.

   

7. The duration of one day on the planet Mercury is equal to 59 Earth days, from this we can conclude that the year on this planet lasts no more than two days a year.

   

8. Mercury rotates very quickly around the Sun, which cannot be said about its speed of rotation around its axis.

   

9. Mercury has a magnetic field. In its center there is an iron core, with the help of which a magnetic field is formed, the strength of which is equal to 1% of the earth's. Despite its small size, on the surface of Mercury there is one of the largest craters in the solar system called Beethoven, whose diameter is 643 kilometers.

   

10. There are a large number of craters on the surface of Mercury, many of them are very tall. They were formed as a result of numerous collisions with passing comets and asteroids. Craters exceeding 250 km in diameter are called basins.

    

11. Man managed to visit the planet twice. Today, research is being conducted in Mercury's orbit thanks to the Messenger probe launched to its surface.

    

12. Until recently, people thought that Mercury had no atmosphere. But the rumors were refuted after the Messenger probe operating in orbit of the planet discovered a thin layer of gas near the surface of Mercury.

    

13. They knew about the mysterious planet Mercury Ancient Rome and Greece. Scientists of that time gave the planet two names. During the day they saw a planet called Apollo, and at night they saw its reflection, which they called Hermes. Later, the Romans gave the planet the name of the god of the merchant - Mercury.

    

14. The crater Heat Plain is located on the surface of the planet.. This name was given to the crater due to its close proximity to “hot longitudes”. In cross-section, the dimensions of the crater are about 1300 km. There is an opinion that many centuries ago the surface of Mercury was damaged by a fallen body whose diameter exceeded 100 km.

    

15. The rotation speed of the planet Mercury is twice that of the planet Earth..

    

As the planet closest to the Sun, Mercury receives much more energy from the central luminary than, for example, the Earth (on average 10 times). Due to the elongation of the orbit, the energy flux from the Sun varies by approximately two times. The long duration of day and night leads to the fact that brightness temperatures (measured by infrared radiation in accordance with Planck’s law of thermal radiation) on the “day” and “night” sides of the surface of Mercury at an average distance from the Sun can vary from approximately 90 K to 700 K (-180 o C to +430 o C). At the same time, the temperature in the polar region reaches - 210 o C at night, and during the day under the scorching rays of the Sun in the equatorial zone + 500 o C. But already at a depth of several tens of centimeters there are no significant temperature fluctuations, which is a consequence of the very low thermal conductivity of rocks. Mercury's polar regions may have water ice. The sun never illuminates the interior areas of the craters located there, and the temperature there can remain around -210°C. Mercury's albedo is extremely low, about 0.11. In 1970, T. Murdock and E. Ney from the University of Minnesota found that the average temperature of the night hemisphere is -162 ° C (111 K). On the other hand, the temperature of the subsolar point at the average distance of Mercury from the Sun is +347°C.
In 1992, during radar observations from the Earth near the northern and south poles planet, areas were discovered for the first time that highly reflect radio waves. It was these data that were interpreted as evidence of the presence of ice in the near-surface layer of Mercury. Radar from the Arecibo radio observatory located on the island of Puerto Rico, as well as from NASA's Deep Space Communications Center in Goldstone (California), revealed about 20 round spots several tens of kilometers across with increased radio reflection. Presumably these are craters, into which, due to their close location to the poles of the planet, the sun's rays fall only briefly or not at all. Such craters, called permanently shadowed, are also present on the Moon; measurements from satellites revealed the presence of a certain amount of water ice. Calculations have shown that the depressions of permanently shadowed craters near Mercury's poles can be cold enough (-175°C) for ice to exist there for a long time. Even in flat areas near the poles, the estimated daily temperature does not exceed -105°C.
Mercury's surface is reminiscent of the moon, covered with thousands of craters formed from collisions with meteorites and rocks that formed when the young core cooled and contracted, pulling together the planet's crust, as well as crushed basalt-type material, and is quite dark. During research carried out by the Messenger probe, over 80% of the surface of Mercury was photographed and found to be homogeneous. In this way, Mercury is not similar to the Moon or Mars, in which one hemisphere is sharply different from the other. There are mountains on Mercury, the highest ones reach 2-4 km. In a number of areas of the planet, valleys and craterless plains are visible on the surface. Judging by observations from Earth and photographs from spacecraft, it is generally similar to the surface of the Moon, although the contrast between dark and light areas is less pronounced. Along with craters (usually shallower than those on the Moon) there are hills and valleys. The largest crater on Mercury is named after the great German composer Beethoven, its diameter is 625 km.
Up to 70% of the studied area is occupied by an ancient, heavily cratered surface. The most significant feature is the Zhara Plain (Caloris Basin), a huge impact crater with a diameter of 1300 km (a quarter of the planet's diameter). The depression was filled with lava and relatively smoothed, with the same type of surface also covering part of the ejecta region. The impact occurred 3800 million years ago, causing a temporary revival of volcanic activity that had largely ceased 100 million years earlier. This led to a smoothing of the areas in and around the depression. In that area of ​​Mercury's surface, which is diametrically opposite to the point of impact, a surprisingly chaotic structure is observed, apparently created by the shock wave.
Characteristic features found on Mercury are rugged cliffs (lobe-shaped ledges - scarps), which take the form of cliffs. They were called ledges because their outlines on the map are characterized by rounded protrusions - “blades” up to several tens of kilometers in diameter. The height of the ledges is from 0.5 to 3 km, while the largest of them reach 500 km in length. These ledges are quite steep, but unlike lunar tectonic ledges, which have a pronounced downward bend in the slope, the Mercurian lobe-shaped ones have a smoothed line of inflection of the surface in their upper part. These ledges are located in the ancient continental regions of the planet. They are believed to have formed during compression of the planetary crust during the cooling process. In some places they cross the walls of craters. Calculations of the compression value indicate a reduction in the area of ​​the crust by 100 thousand sq km, which corresponds to a decrease in the radius of the planet by 1-2 km. (cooling and solidification of the planet’s interior). Radar observations of Mercury at the end of 2001 showed the presence of a large crater with a diameter of 85 km on its surface. It is similar in structure to the Tycho crater on the lunar surface, but may be significantly younger than the 109-million-year-old lunar formation.

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