0.147 Earth
0.056 Earth
0.055 Earth
0.984 Earth
0,38
281.01°
0.106 (geom. albedo)
24.9% sodium
9.5%, A. oxygen
7.0% argon
5.9% helium
5.6%, M. oxygen
5.2% nitrogen
3.6% carbon dioxide
3.4% water
3.2% hydrogen
Mercury in natural color (Mariner 10 image)
Mercury- the planet closest to the Sun in the Solar System, orbits the Sun in 88 Earth days. Mercury is classified as an inner planet because its orbit is closer to the Sun than the main asteroid belt. 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 −2.0 to 5.5, but it is not easily visible due to its very 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 always hidden in the morning or evening dawn. 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).
It is convenient to observe Mercury at low latitudes and near the equator: this is due to the fact that the duration of twilight there is shortest. In mid-latitudes it is much more difficult to find Mercury and only during the period of the best elongations, and in high latitudes it is impossible at all.
Relatively little is known about the planet yet. The Mariner 10 apparatus, which studied Mercury in -1975, managed to map only 40-45% of the surface. In January 2008, the interplanetary station MESSENGER flew past Mercury, which will enter orbit around the planet in 2011.
According to their own physical characteristics Mercury resembles the Moon and is heavily cratered. 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 0.1 of the Earth’s. Mercury's core makes up 70 percent of the planet's total volume. The temperature on the surface of Mercury ranges from 90 to 700 (−180 to +430 °C). The solar side heats up much more than the polar regions and the far side of the planet.
Despite its smaller radius, Mercury still exceeds in mass such satellites of the giant planets as Ganymede and Titan.
The astronomical symbol of Mercury is a stylized image of the winged helmet of the god Mercury with his caduceus.
History and name
The oldest evidence of observations of Mercury can be found in Sumerian cuneiform texts dating back to the third millennium BC. e. The planet is named after the god of the Roman pantheon Mercury, analogue of Greek Hermes and Babylonian Naboo. The ancient Greeks of Hesiod's time called Mercury "Στίλβων" (Stilbo, the Shining One). Until the 5th century BC. e. The Greeks believed that Mercury, visible in the evening and morning skies, were two different objects. In ancient India, Mercury was called Buddha(बुध) and Roginea. In Chinese, Japanese, Vietnamese and Korean, Mercury is called water star(水星) (in accordance with the ideas of the “Five Elements”. In Hebrew, the name of Mercury sounds like “Kohav Hama” (כוכב חמה) (“Solar Planet”).
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 the Sun than at aphelion. The inclination of the orbit to the ecliptic plane is 7°. Mercury spends 87.97 days on one orbital revolution. The average speed of the planet's orbit is 48 km/s.
For a long time it was believed that Mercury constantly faces the Sun with the same side, and one revolution around its axis takes the same 87.97 days. Observations of details on the surface of Mercury, carried out at the limit of resolution, did not seem to contradict this. This misconception was due to the fact 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 rotation period of Mercury (352 days), therefore approximately the same surface area was observed at different times planets. On the other hand, some astronomers believed that Mercury's day was approximately equal to Earth's. 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. This commensurability of the periods of rotation and revolution of Mercury 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 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, 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.
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 speed of orbital motion exceeds the speed 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 of the Book of Joshua from the Bible, who stopped the movement of the Sun (Joshua, X, 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, it is Mercury that is most of the time the planet closest to Earth than any other (since the others move away at to a greater extent, without being so “attached” to the Sun).
Physical characteristics
Comparative sizes of Mercury, Venus, Earth and Mars
Mercury is the smallest terrestrial planet. Its radius is only 2439.7 ± 1.0 km, which is smaller than the radius of Jupiter's moon Ganymede and Saturn's moon Titan. The mass of the planet is 3.3 × 10 23 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. The acceleration of gravity on Mercury is 3.70 m/s². The second escape velocity is 4.3 km/s.
Kuiper Crater (just below center). Photo from MESSENGER spacecraft
One of the most noticeable features of the surface of Mercury is the Plain of Heat (lat. Caloris Planitia). This crater got its name because it is located near one of the “hot longitudes”. Its diameter is about 1300 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 intersected “chaotic” landscape here.
Atmosphere and physical fields
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 × 10 11 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. It consists 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 a certain atom in the atmosphere is about 200 days.
Mercury has a magnetic field whose strength is 300 times less than the Earth's magnetic field. Mercury's magnetic field has a dipole structure and highest degree symmetrically, and its axis deviates only 2 degrees from the axis of rotation of the planet, which imposes a significant limitation on the range of theories explaining its origin.
Research
An image of a section of Mercury's surface taken by MESSENGER
Mercury is the least studied terrestrial planet. Only two devices were sent to study it. The first was Mariner 10, which flew past Mercury three times in -1975; the closest approach was 320 km. As a result, several thousand images were obtained, covering approximately 45% of the planet's surface. Further research from Earth showed the possibility of the existence of water ice in polar craters.
Mercury in art
- In Boris Lyapunov's science fiction story "Nearest to the Sun" (1956), Soviet cosmonauts land on Mercury and Venus for the first time to study them.
- Isaac Asimov's story "Mercury's Big Sun" (Lucky Starr series) takes place on Mercury.
- Isaac Asimov's stories "Runaround" and "The Dying Night", written in 1941 and 1956 respectively, describe Mercury with one side facing the Sun. Moreover, in the second story, the solution to the detective plot is based on this fact.
- In the science fiction novel The Flight of the Earth by Francis Karsak, along with the main plot, a scientific station for studying the Sun, located at the North Pole of Mercury, is described. Scientists live at a base located in the eternal shadow of deep craters, and observations are carried out from giant towers constantly illuminated by the luminary.
- In Alan Nurse's science fiction story "Across the Sunny Side", the main characters cross the side of Mercury facing the Sun. The story was written in accordance with the scientific views of its time, when it was assumed that Mercury was constantly facing the Sun with one side.
- In the anime animated series Sailor Moon, the planet is personified by the warrior girl Sailor Mercury, aka Ami Mitsuno. Her attack is based on the power of water and ice.
- In Clifford Simak's science fiction story "Once Upon a Time on Mercury", the main field of action is Mercury, and the energy form of life on it - balls - surpasses humanity by millions of years of development, having long passed the stage of civilization.
Notes
See also
Literature
- Bronshten V. Mercury is closest to the Sun // Aksenova M.D. Encyclopedia for children. T. 8. Astronomy - M.: Avanta+, 1997. - P. 512-515. - ISBN 5-89501-008-3
- Ksanfomality L.V. Unknown Mercury // In the world of science. - 2008. - № 2.
Links
- Website about the MESSENGER mission (English)
- Photos of Mercury taken by Messenger (English)
- BepiColombo mission section on the JAXA website
- A. Levin. Iron Planet Popular Mechanics No. 7, 2008
- “The closest” Lenta.ru, October 5, 2009, photographs of Mercury taken by Messenger
- “New photographs of Mercury have been published” Lenta.ru, November 4, 2009, about the rapprochement of Messenger and Mercury on the night of September 29-30, 2009
Mercury is the smallest and closest planet to the Sun in the 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.
Brief description
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. 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 terrestrial planet 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 the presence of the planet’s own magnetic field, albeit weak, is a strong argument in favor of the version of its liquid core. The movement of matter inside the nucleus causes a dynamo effect, and the strong elongation of the orbit causes a tidal effect, which maintains the nucleus 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 during 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. At a minimum distance from the Earth, it is visible as a thin crescent. 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 was given decades later by general theory Einstein's 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.
0.147 Earth
0.056 Earth
0.055 Earth
0.984 Earth
0,38
281.01°
0.106 (geom. albedo)
24.9% sodium
9.5%, A. oxygen
7.0% argon
5.9% helium
5.6%, M. oxygen
5.2% nitrogen
3.6% carbon dioxide
3.4% water
3.2% hydrogen
Mercury in natural color (Mariner 10 image)
Mercury- the planet closest to the Sun in the Solar System, orbits the Sun in 88 Earth days. Mercury is classified as an inner planet because its orbit is closer to the Sun than the main asteroid belt. 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 −2.0 to 5.5, but it is not easily visible due to its very 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 always hidden in the morning or evening dawn. 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).
It is convenient to observe Mercury at low latitudes and near the equator: this is due to the fact that the duration of twilight there is shortest. In mid-latitudes it is much more difficult to find Mercury and only during the period of the best elongations, and in high latitudes it is impossible at all.
Relatively little is known about the planet yet. The Mariner 10 apparatus, which studied Mercury in -1975, managed to map only 40-45% of the surface. In January 2008, the interplanetary station MESSENGER flew past Mercury, which will enter orbit around the planet in 2011.
In its physical characteristics, Mercury resembles the Moon and is heavily cratered. 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 0.1 of the Earth’s. Mercury's core makes up 70 percent of the planet's total volume. The temperature on the surface of Mercury ranges from 90 to 700 (−180 to +430 °C). The solar side heats up much more than the polar regions and the far side of the planet.
Despite its smaller radius, Mercury still exceeds in mass such satellites of the giant planets as Ganymede and Titan.
The astronomical symbol of Mercury is a stylized image of the winged helmet of the god Mercury with his caduceus.
History and name
The oldest evidence of observations of Mercury can be found in Sumerian cuneiform texts dating back to the third millennium BC. e. The planet is named after the god of the Roman pantheon Mercury, analogue of Greek Hermes and Babylonian Naboo. The ancient Greeks of Hesiod's time called Mercury "Στίλβων" (Stilbo, the Shining One). Until the 5th century BC. e. The Greeks believed that Mercury, visible in the evening and morning skies, were two different objects. In ancient India, Mercury was called Buddha(बुध) and Roginea. In Chinese, Japanese, Vietnamese and Korean, Mercury is called water star(水星) (in accordance with the ideas of the “Five Elements”. In Hebrew, the name of Mercury sounds like “Kohav Hama” (כוכב חמה) (“Solar Planet”).
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 the Sun than at aphelion. The inclination of the orbit to the ecliptic plane is 7°. Mercury spends 87.97 days on one orbital revolution. The average speed of the planet's orbit is 48 km/s.
For a long time it was believed that Mercury constantly faces the Sun with the same side, and one revolution around its axis takes the same 87.97 days. Observations of details on the surface of Mercury, carried out at the limit of resolution, did not seem to contradict this. This misconception was due to the fact 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 rotation period of Mercury (352 days), therefore approximately the same surface area was observed at different times planets. On the other hand, some astronomers believed that Mercury's day was approximately equal to Earth's. 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. This commensurability of the periods of rotation and revolution of Mercury 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 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, 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.
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 speed of orbital motion exceeds the speed 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 of the Book of Joshua from the Bible, who stopped the movement of the Sun (Joshua, X, 12-13). For an observer at longitudes 90° away from the “hot longitudes,” the Sun rises (or sets) twice.
It is also interesting that although Mars and Venus are the closest in orbit to Earth, it is Mercury that is most of the time the closest planet to Earth than any other (since the others move away more, not being so “tied” to the Sun).
Physical characteristics
Comparative sizes of Mercury, Venus, Earth and Mars
Mercury is the smallest terrestrial planet. Its radius is only 2439.7 ± 1.0 km, which is smaller than the radius of Jupiter's moon Ganymede and Saturn's moon Titan. The mass of the planet is 3.3 × 10 23 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. The acceleration of gravity on Mercury is 3.70 m/s². The second escape velocity is 4.3 km/s.
Kuiper Crater (just below center). Photo from MESSENGER spacecraft
One of the most noticeable features of the surface of Mercury is the Plain of Heat (lat. Caloris Planitia). This crater got its name because it is located near one of the “hot longitudes”. Its diameter is about 1300 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 intersected “chaotic” landscape here.
Atmosphere and physical fields
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 × 10 11 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. It consists 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 a certain atom in the atmosphere is about 200 days.
Mercury has a magnetic field whose strength is 300 times less than the Earth's magnetic field. Mercury's magnetic field has a dipole structure and is highly symmetrical, and its axis deviates only 2 degrees from the planet's axis of rotation, which imposes a significant limitation on the range of theories explaining its origin.
Research
An image of a section of Mercury's surface taken by MESSENGER
Mercury is the least studied terrestrial planet. Only two devices were sent to study it. The first was Mariner 10, which flew past Mercury three times in -1975; the closest approach was 320 km. As a result, several thousand images were obtained, covering approximately 45% of the planet's surface. Further research from Earth showed the possibility of the existence of water ice in polar craters.
Mercury in art
- In Boris Lyapunov's science fiction story "Nearest to the Sun" (1956), Soviet cosmonauts land on Mercury and Venus for the first time to study them.
- Isaac Asimov's story "Mercury's Big Sun" (Lucky Starr series) takes place on Mercury.
- Isaac Asimov's stories "Runaround" and "The Dying Night", written in 1941 and 1956 respectively, describe Mercury with one side facing the Sun. Moreover, in the second story, the solution to the detective plot is based on this fact.
- In the science fiction novel The Flight of the Earth by Francis Karsak, along with the main plot, a scientific station for studying the Sun, located at the North Pole of Mercury, is described. Scientists live at a base located in the eternal shadow of deep craters, and observations are carried out from giant towers constantly illuminated by the luminary.
- In Alan Nurse's science fiction story "Across the Sunny Side", the main characters cross the side of Mercury facing the Sun. The story was written in accordance with the scientific views of its time, when it was assumed that Mercury was constantly facing the Sun with one side.
- In the anime animated series Sailor Moon, the planet is personified by the warrior girl Sailor Mercury, aka Ami Mitsuno. Her attack is based on the power of water and ice.
- In Clifford Simak's science fiction story "Once Upon a Time on Mercury", the main field of action is Mercury, and the energy form of life on it - balls - surpasses humanity by millions of years of development, having long passed the stage of civilization.
Notes
See also
Literature
- Bronshten V. Mercury is closest to the Sun // Aksenova M.D. Encyclopedia for children. T. 8. Astronomy - M.: Avanta+, 1997. - P. 512-515. - ISBN 5-89501-008-3
- Ksanfomality L.V. Unknown Mercury // In the world of science. - 2008. - № 2.
Links
- Website about the MESSENGER mission (English)
- Photos of Mercury taken by Messenger (English)
- BepiColombo mission section on the JAXA website
- A. Levin. Iron Planet Popular Mechanics No. 7, 2008
- “The closest” Lenta.ru, October 5, 2009, photographs of Mercury taken by Messenger
- “New photographs of Mercury have been published” Lenta.ru, November 4, 2009, about the rapprochement of Messenger and Mercury on the night of September 29-30, 2009
The planet Mercury is closest to the Sun. It is the smallest terrestrial planet without satellites located in our solar system. In 88 days (about 3 months), it makes 1 revolution around our Sun.
The best photographs were taken from the only space probe, Mariner 10, sent to explore Mercury back in 1974. These images clearly show that almost the entire surface of Mercury is strewn with craters, and therefore is quite similar to the lunar structure. Most of them were formed during collisions with meteorites. There are plains, mountains and plateaus. There are also ledges, the height of which can reach up to 3 kilometers. All these irregularities are associated with the fracture of the crust, due to sudden temperature changes, sudden cooling and subsequent warming. Most likely, this happened during the formation of the planet.
The presence of a dense metallic core in Mercury is characterized by high density and a strong magnetic field. The mantle and crust are quite thin, which means that almost the entire planet consists of heavy elements. According to modern calculations, the density in the center of the planet’s core reaches almost 10 g/cm3, and the radius of the core is 75% of the radius of the planet and is equal to 1800 km. It is rather doubtful that the planet had such a huge and heavy iron-containing core from the very beginning. Scientists believe that in the event of a strong collision with another celestial body during formation solar system, a significant part of the mantle broke off.
Mercury's orbit
Mercury's orbit is eccentric and is located approximately 58,000,000 km from the Sun. When moving in orbit, the distance changes to 24,000,000 km. The speed of rotation depends on the position of the planet to the Sun. At aphelion - the point of the orbit of a planet or other planet farthest from the Sun celestial body–Mercury moves at a speed of about 38 km/s, and at perihelion – the point of its orbit closest to the Sun – its speed is 56 km/s. Thus, average speed Mercury's movement is about 48 km/s. Since both the Moon and Mercury are located between the Earth and the Sun, their phases have many common features. At its closest point to Earth, it has the shape of a thin crescent phase. But due to its very close position to the Sun, its full phase is very difficult to see.
Day and night on Mercury
One of the hemispheres of Mercury faces the Sun for a long time due to its slow rotation. Therefore, the change of day and night occurs there much less frequently than on other planets of the solar system, and in general, it is practically unnoticeable. Day and night on Mercury are equal to a year of the planet, because they last a full 88 days! Also, Mercury is characterized by significant temperature changes: during the day the temperature rises to +430 °C, and at night it drops to -180 °C. Mercury's axis is almost perpendicular to the orbital plane, and is only 7°, so there is no change of seasons here. But, near the poles, there are places where sunlight never penetrates.
Characteristics of Mercury
Weight: 3.3*1023 kg (0.055 Earth mass)
Diameter at the equator: 4880 km
Axis tilt: 0.01°
Density: 5.43 g/cm3
Average surface temperature: –73 °C
Period of rotation around the axis (days): 59 days
Distance from the Sun (average): 0.390 a. e. or 58 million km
Orbital period around the Sun (year): 88 days
Orbital speed: 48 km/s
Orbital eccentricity: e = 0.0206
Orbital inclination to the ecliptic: i = 7°
Gravity acceleration: 3.7 m/s2
Satellites: no
The surface of Mercury, in short, resembles the Moon. Vast plains and many craters indicate that geological activity on the planet ceased billions of years ago.
Surface character
The surface of Mercury (photo shown later in the article), taken by the Mariner 10 and Messenger probes, looked similar in appearance to the Moon. The planet is largely littered with craters different sizes. The smallest ones visible in the most detailed photographs of Mariner measure several hundred meters in diameter. The space between large craters is relatively flat and consists of plains. It is similar to the surface of the Moon, but takes up much more space. Similar areas surround Mercury's most prominent impact structure, the Caloris Planitia basin. Only half of it was illuminated when Mariner 10 encountered it, but it was fully discovered by Messenger during its first flyby of the planet in January 2008.
Craters
The most common landforms on the planet are craters. They largely cover the surface (photos below) at first glance similar to the Moon, but upon closer examination they reveal interesting differences.
Mercury's gravity is more than twice that of the Moon, partly due to the density of its huge core of iron and sulfur. The strong force of gravity tends to keep the material ejected from the crater close to the collision site. Compared to the Moon, it fell at a distance of only 65% of the lunar distance. This may be one of the factors that contributed to the appearance of secondary craters on the planet, formed under the influence of ejected material, in contrast to the primary ones, which arose directly from a collision with an asteroid or comet. More high strength gravity means that the complex shapes and structures characteristic of large craters - central peaks, steep slopes and flat bases - are observed in smaller craters on Mercury (minimum diameter of about 10 km) than on the Moon (about 19 km). Structures smaller than these sizes have simple bowl-like outlines. Mercury's craters are different from those on Mars, although the two planets have comparable gravity. Fresh craters on the first are, as a rule, deeper than comparable formations on the second. This may be a consequence of the low volatile content of Mercury's crust or higher impact velocities (as the speed of an object in solar orbit increases as it approaches the Sun).
Craters larger than 100 km in diameter begin to approach the oval shape characteristic of such large entities. These structures - polycyclic basins - have dimensions of 300 km or more and are the result of the most powerful collisions. Several dozen of them were discovered on the photographed part of the planet. Messenger images and laser altimetry have made major contributions to understanding these residual scars from early asteroid bombardments on Mercury.
Plain of Heat
This impact structure extends over 1550 km. When it was initially discovered by Mariner 10, it was thought to be much smaller. The interior of the object consists of smooth plains covered with folded and broken concentric circles. The largest ridges extend several hundred kilometers in length, about 3 km in width and less than 300 meters in height. More than 200 fractures, comparable in size at the edges, emanate from the center of the plain; many of them are depressions bounded by grooves (grabens). Where grabens intersect with ridges, they tend to pass through them, indicating their later formation.
Surface types
The Zhary Plain is surrounded by two types of terrain - its edge and the relief formed by discarded rock. The edge is a ring of irregular mountain blocks, reaching 3 km in height, which are the most high mountains, found on a planet with relatively steep slopes towards the center. The second, much smaller ring is located 100-150 km from the first. Beyond the outer slopes is a zone of linear radial ridges and valleys, partially filled with plains, some of which are dotted with numerous mounds and hills several hundred meters high. The origin of the formations that make up the wide rings around the Zhara basin is controversial. Some plains on the Moon were formed largely by the interaction of ejecta with pre-existing surface topography, and this may also be true for Mercury. But the Messenger results suggest that volcanic activity played a significant role in their formation. Not only are there few craters there compared to the Zhara Basin, indicating a protracted period of plain formation, but they have other features more clearly associated with volcanism than could be seen in the Mariner 10 images. Crucial evidence of volcanism came from Messenger images showing volcanic vents, many of which lie along the outer edge of the Zhara Plain.
Raditladi Crater
Caloris is one of the youngest large polycyclic plains, at least on the explored part of Mercury. It probably formed at the same time as the last giant structure on the Moon - about 3.9 billion years ago. Messenger images revealed another, much smaller impact crater with a visible inner ring that may have formed much later, called the Raditladi Basin.
Strange antipode
On the other side of the planet, exactly 180° opposite the Plain of Heat, is a patch of strangely distorted terrain. Scientists interpret this fact by talking about their simultaneous formation by focusing seismic waves from events that affected the antipodal surface of Mercury. The hilly and line-dotted terrain is a vast area of uplands, which are hilly polygons 5-10 km wide and up to 1.5 km high. Pre-existing craters were transformed into hills and cracks by seismic processes, as a result of which this relief was formed. Some of them had a flat bottom, but then its shape changed, indicating their later filling.
Plains
A plain is the relatively flat or gently undulating surface of Mercury, Venus, Earth and Mars and is found throughout these planets. It represents the “canvas” on which the landscape developed. The plains are evidence of the process of destruction of rough terrain and the creation of smoothed space.
There are at least three methods of “grinding” that probably smoothed the surface of Mercury.
One way - increasing temperature - reduces the strength of the bark and its ability to hold high relief. Over millions of years, the mountains will “sink”, the bottom of the craters will rise and the surface of Mercury will level out.
The second method involves moving rocks towards lower areas of the area under the influence of gravity. Over time, the rock accumulates in the lowlands and fills more high levels as its volume increases. This is how lava flows from the bowels of the planet behave.
The third method is for rock fragments to fall onto the surface of Mercury from above, which ultimately leads to the leveling of rough terrain. Examples of this mechanism include rock emissions from cratering and volcanic ash.
Volcanic activity
Some evidence favoring the hypothesis of the influence of volcanic activity on the formation of many of the plains surrounding the Zhara basin has already been given. Other relatively young plains on Mercury, particularly visible in regions illuminated at low angles during Messenger's first flyby, show characteristic features volcanism. For example, several old craters were filled to the brim with lava flows, similar to similar formations on the Moon and Mars. However, widespread plains on Mercury are more difficult to assess. Because they are older, it is clear that volcanoes and other volcanic features may have eroded or otherwise collapsed, making them difficult to explain. Understanding these old plains is important because they are likely responsible for the disappearance of most of the 10-30 km diameter craters compared to the Moon.
Scarps
The most important landforms of Mercury, which provide an idea of internal structure planets, are hundreds of jagged ledges. The length of these rocks varies from tens to more than thousands of kilometers, and their heights range from 100 m to 3 km. When viewed from above, their edges appear rounded or jagged. It is clear that this is the result of cracking, when part of the soil rose and lay on the surrounding area. On Earth, such structures are limited in volume and arise during local horizontal compression in earth's crust. But the entire explored surface of Mercury is covered with scarps, which means that the planet’s crust has shrunk in the past. From the number and geometry of scarps it follows that the planet has decreased in diameter by 3 km.
Moreover, the shrinkage must have continued until relatively recently. geological history time, as some scarps have altered the shape of well-preserved (and therefore relatively young) impact craters. The slowing down of the planet's initially high rotation rate by tidal forces produced compression in Mercury's equatorial latitudes. The globally distributed scarps, however, suggest another explanation: late cooling of the mantle, perhaps combined with the solidification of part of the once completely molten core, led to compression of the core and deformation of the cold crust. The contraction of Mercury's size as its mantle cooled should have resulted in more longitudinal structures than can be seen, indicating that the contraction process was not complete.
The surface of Mercury: what is it made of?
Scientists have tried to figure out the composition of the planet by studying sunlight reflected from different parts of it. One difference between Mercury and the Moon, besides the former being slightly darker, is that it has a smaller spectrum of surface brightnesses. For example, the seas of Earth's moon—smooth expanses visible to the naked eye as large dark spots—are much darker than the cratered highlands, and the plains of Mercury are only slightly darker. The color differences on the planet are less pronounced, although Messenger images taken using a set of color filters showed small, very colorful areas associated with volcanic vents. These features, as well as the relatively featureless visible and near-infrared spectrum of the reflected sunlight, suggest that the surface of Mercury consists of silicate minerals, not rich in iron and titanium, of a darker color, compared to the lunar seas. In particular, the planet's rocks may be low in iron oxides (FeO), leading to speculation that it was formed under much more reducing conditions (i.e., lack of oxygen) than other members of the terrestrial group.
Problems of remote research
It is very difficult to determine the planet's composition by remotely sensing sunlight and the thermal spectrum that Mercury's surface reflects. The planet is heating up greatly, which changes the optical properties of mineral particles and complicates direct interpretation. However, Messenger was equipped with several instruments not present on Mariner 10 that measured chemical and mineral composition directly. These instruments required a long observation period while the craft remained near Mercury, so no concrete results were available after the first three short flybys. It was only during the Messenger orbital mission that enough new information about the composition of the planet's surface.