Mercury occupies the first place in the list of planets of our solar system. Despite the rather modest size, this planet has an honorable role: to be closest to our star, to be approached by the cosmic body of our luminary. However, this location cannot be called very successful. Mercury is the closest planet to the Sun and is forced to endure the full force of the hot love and warmth of our star.
Astrophysical characteristics and features of the planet
Mercury is the smallest planet in the solar system, belonging together with Venus, Earth and Mars to the terrestrial planets. The average radius of the planet is only 2439 km, and the diameter of this planet at the equator is 4879 km. It should be noted that the size makes the planet not only the smallest among other planets in the solar system. In size, it is even smaller than some of the largest satellites.
Jupiter's satellite Ganymede and Saturn's satellite Titan have a diameter of over 5,000 km. Jupiter's moon Callisto is about the same size as Mercury.
The planet is named after the sly and swift Mercury, the ancient Roman god of trade. The choice of name is not accidental. A small and nimble planet moves the fastest in the sky. The movement and length of the orbital path around our star takes 88 Earth days. This speed is due to the close location of the planet to our star. The planet is at a distance from the Sun within 46-70 million km.
The following astrophysical characteristics of the planet should be added to the small size of the planet:
- the mass of the planet is 3 x 1023 kg or 5.5% of the mass of our planet;
- the density of a small planet is slightly inferior to that of the earth and equals 5.427 g/cm3;
- the gravitational force on it or the free fall acceleration is 3.7 m/s2;
- the surface area of the planet is 75 million square meters. kilometers, i.e. only 10% of the earth's surface area;
- the volume of Mercury is 6.1 x 1010 km3 or 5.4% of the volume of the Earth, i.e. 18 such planets would fit in our Earth.
Rotation of Mercury around own axis occurs with a frequency of 56 Earth days, while a Mercury day lasts half an Earth year on the surface of the planet. In other words, during a Mercury day, Mercury basks in the rays of the Sun for 176 Earth days. In this situation, one side of the planet is heated to extreme temperatures, while the other side of Mercury at this time cools to a state of cosmic cold.
There are very interesting facts about the state of the orbit of Mercury and the position of the planet in relation to other celestial bodies. There is practically no change of seasons on the planet. In other words, there is a sharp transition from a hot and hot summer to a fierce cosmic winter. This is due to the fact that the planet has an axis of rotation located perpendicular to the orbital plane. As a result of this position of the planet, there are areas on its surface that the sun's rays never touch. The data obtained from the Mariner space probes confirmed that on Mercury, as well as on the Moon, suitable water was found, which, however, is in a frozen state and is located deep under the surface of the planet. At the moment, it is believed that such areas can be found in areas close to the regions of the poles.
Another interesting property that characterizes the orbital position of the planet is the discrepancy between the speed of rotation of Mercury around its own axis and the movement of the planet around the Sun. The planet has a constant frequency of revolution, while it runs around the Sun at different speeds. Near perihelion, Mercury moves faster than angular velocity rotation of the planet itself. This discrepancy causes an interesting astronomical phenomenon - the Sun begins to move across the Mercury sky in the opposite direction, from the West to the east.
Given the fact that Venus is considered to be the closest planet to Earth, Mercury is often much closer to our planet than the “morning star”. The planet has no satellites, so it accompanies our star in splendid isolation.
Atmosphere of Mercury: origin and current state
Despite its close position to the Sun, the surface of the planet is separated from the star by an average of 5-7 tens of millions of kilometers, but the most significant daily temperature drops are observed on it. During the day, the surface of the planet is heated to the state of a hot frying pan, the temperature of which is 427 degrees Celsius. At night, cosmic cold prevails here. The surface of the planet has a low temperature, its maximum reaches minus 200 degrees Celsius.
The reason for such extreme temperature fluctuations lies in the state of the Mercury atmosphere. It is in an extremely rarefied state, having no effect on the thermodynamic processes on the surface of the planet. Atmospheric pressure here is very low and is only 10-14 bar. The atmosphere has a very weak influence on the climatic conditions of the planet, which is determined by the orbital position in relation to the Sun.
Basically, the atmosphere of the planet consists of molecules of helium, sodium, hydrogen and oxygen. These gases were either captured by the planet's magnetic field from solar wind particles or originated from the evaporation of the Mercury surface. The rarefiedness of the atmosphere of Mercury is evidenced by the fact that its surface is clearly visible not only from the board of automatic orbital stations, but also through a modern telescope. There is no cloudiness above the planet, opening up free access to the Mercury surface for the sun's rays. Scientists believe that this state of the Mercury atmosphere is explained by the close position of the planet to our star, its astrophysical parameters.
For a long time, astronomers had no idea what color Mercury was. However, observing the planet through a telescope and looking at pictures taken from spacecraft, scientists discovered a gray and unattractive Mercury disk. This is due to the lack of an atmosphere on the planet and the rocky landscape.
Strength magnetic field obviously unable to resist the influence of the gravitational force that the Sun exerts on the planet. Solar wind streams supply the planet's atmosphere with helium and hydrogen, but due to constant heating, the heated gases dissipate back into outer space.
Brief description of the structure and composition of the planet
In this state of the atmosphere, Mercury is not able to defend itself against the attack of cosmic bodies falling on the surface of the planet. There are no signs of natural erosion on the planet, the surface is more likely to be affected by cosmic processes.
Like other terrestrial planets, Mercury has its own firmament, but unlike the Earth and Mars, which are mainly composed of silicates, it is 70% metal. This explains the rather high density of the planet and its mass. In many physical parameters, Mercury is very much like our satellite. As on the Moon, the surface of the planet is a lifeless desert, devoid of a dense atmosphere and open to cosmic influence. At the same time, the crust and mantle of the planet have a thin layer, if compared with terrestrial geological parameters. The inner part of the planet is mainly represented by a heavy iron core. It has a core, which consists entirely of molten iron and occupies almost half of the entire planetary volume and ¾ of the planet's diameter. Only an insignificant mantle, only 600 km thick, represented by silicates, separates the core of the planet from the crust. The layers of the Mercurial crust have different thicknesses, which vary in the range of 100-300 km.
This explains the very high density of the planet, which is uncharacteristic of planets similar in size and origin. celestial bodies. The presence of a molten iron core gives Mercury a magnetic field strong enough to counteract the solar wind by trapping charged plasma particles. Such a structure of the planet is uncharacteristic for most planets in the solar system, where the core accounts for 25-35% of the total planetary mass. Probably, such mercurology is caused by the peculiarities of the origin of the planet.
Scientists believe that the composition of the planet was strongly influenced by the origin of Mercury. According to one version, it is a former satellite of Venus, which subsequently lost its rotational momentum and was forced, under the influence of the Sun's gravity, to move into its own elongated orbit. According to other versions, at the formation stage, more than 4.5 billion years ago, Mercury collided with either Venus or another planetesimal, as a result of which most of the Mercury crust was demolished and dispersed in outer space.
The third version of the origin of Mercury is based on the assumption that the planet was formed from the remnants of cosmic matter left after the formation of Venus, Earth and Mars. Heavy elements, mostly metals, formed the core of the planet. To form the outer shell of the planet, lighter elements were clearly not enough.
Judging by the photos taken from space, the time of Mercury activity is long gone. The surface of the planet is a meager landscape, on which the main decoration are craters, large and small, presented in huge numbers. The Mercurial Valleys are vast areas of hardened lava that testify to the past volcanic activity planets. The bark has no tectonic plates and covers the planet's mantle in layers.
The size of the craters on Mercury is amazing. The largest and largest crater, which was called the Heat Plain, has a diameter of more than one and a half thousand kilometers. The giant caldera of the crater, whose height is 2 km, suggests that the collision of Mercury with a cosmic body of this size had the scale of a universal cataclysm.
The early cessation of volcanic activity led to a rapid cooling of the planet's surface and the formation of an undulating landscape. The cooled layers of the crust crawled onto the lower ones, forming scales, and the impacts of asteroids and the fall of large meteorites only more disfigured the face of the planet.
Spacecraft and equipment involved in the study of Mercury
For a long time, we observed cosmic bodies, asteroids, comets, satellites of the planet and stars through telescopes, not having the technical ability to study our cosmic neighborhood in more detail and in detail. We looked at our neighbors and Mercury in a completely different way, including when it became possible to launch space probes and spacecraft to distant planets. We got a completely different idea of what outer space looks like, the objects of our solar system.
The bulk of scientific information about Mercury was obtained as a result of astrophysical observations. The study of the planet was carried out with the help of new powerful telescopes. Significant progress in the study of the smallest planet in the solar system was made by the flight of the American spacecraft Mariner-10. Such an opportunity appeared in November 1973, when the Atlas rocket with an astrophysical automatic probe was launched from Cape Canaveral.
The American space program "Mariner" assumed the launch of a series of automatic probes to the nearest planets, to Venus and Mars. If the first devices were mainly directed towards Venus and Mars, then the last, tenth probe, having studied Venus along the way, flew away towards Mercury. It was the flight of a small spacecraft that gave astrophysicists the necessary information about the surface of the planet, about the composition of the atmosphere and about the parameters of its orbit.
The spacecraft performed surveys of the planet from a flyby trajectory. The flight of the spacecraft was calculated in such a way that Mariner 10 could pass as many times as possible in close proximity to the planet. The first flight took place in March 1974. The device passed from the planet at a distance of 700 km, taking the first pictures of a distant planet from a close distance. During the second flyby, the distance decreased even more. The American probe swept over the surface of Mercury at an altitude of 48 km. For the third time, Mariner 10 was separated from Mercury by a distance of 327 km. As a result of the flights of the Mariner, it was possible to obtain images of the surface of the planet and draw up an approximate map of it. The planet turned out to be seemingly dead, inhospitable and unsuitable for existing and known to science life forms.
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Although the laurels of the smallest planet Mercury got quite recently, because before it was considered the smallest planet, but after it was demoted from the status of "full-fledged" planets, the championship passed to Mercury, about which our today's article.
History of the discovery of the planet Mercury
The history of Mercury and our knowledge of this planet goes back to ancient times, in fact it is one of the first planets known to mankind. So Mercury was observed in ancient Sumer, one of the first developed civilizations on Earth. Among the Sumerians, Mercury was associated with the local god of writing, Nabu. The Babylonian and ancient Egyptian priests, concurrently excellent astronomers of the ancient world, also knew about this planet.
As for the origin of the name of the planet "Mercury", it already comes from the Romans, who named this planet in honor of the ancient god Mercury (in the Greek version of Hermes), the patron of trade, crafts and the messenger of other Olympic gods. Also, astronomers of the past sometimes poetically called Mercury the morning or evening dawn, according to the time of its appearance in the starry sky.
The god Mercury, after whom the planet was named.
Also, ancient astronomers believed that Mercury and its closest neighbor planet Venus revolve around the Sun, and not around the Earth. And now, in turn, it revolves around the Earth.
Features of the planet Mercury
Perhaps the most interesting feature of this small planet is the fact that it is on Mercury that the largest temperature fluctuations occur: since Mercury is closest to the Sun, during the day its surface warms up to 450 C. But on the other hand, Mercury does not have its own atmosphere and cannot retain heat, as a result, at night the temperature drops to minus 170 C, here the largest temperature difference in our solar system.
Mercury is only slightly larger than our Moon. Its surface is also similar to the moon, riddled with craters, traces of small asteroids and meteorites.
An interesting fact: about 4 billion years ago, a huge asteroid crashed into Mercury, the force of this impact can be compared with the explosion of a trillion megaton bombs. This impact left a giant crater on the surface of Mercury, about the size of the modern state of Texas, astronomers called it the Basins Caloris crater.
Also very interesting is the fact that there is real ice on Mercury, which is hidden in the depths of the craters there. Ice could have been brought to Mercury by meteorites, or even formed from water vapor that escapes from the planet's interior.
Another interesting feature of this planet is the decrease in its size. The decrease itself is believed by scientists to be caused by the gradual cooling of the planet, which occurs over millions of years. As a result of cooling, its surface is crushed and blade-shaped rocks are formed.
The density of Mercury is high, only our Earth is higher, in the center of the planet there is a huge core, which is 75% of the diameter of the entire planet.
With the help of the Mariner 10 research probe sent by NASA to the surface of Mercury, an amazing discovery was made - there is a magnetic field on Mercury. This was all the more surprising, since according to the astrophysical data of this planet: the speed of rotation and the presence of a molten core, there should not be a magnetic field there. Despite the fact that the strength of the magnetic field of Mercury is only 1% of the strength of the Earth's magnetic field, it is superactive - the magnetic field of the solar wind periodically enters the field of Mercury and, from interaction with it, strong magnetic tornadoes arise, sometimes reaching the surface of the planet.
The speed of the planet Mercury, at which it revolves around the Sun, is 180,000 km per hour. The orbit of Mercury is oval and strongly elongated epileptically, as a result of which it either approaches the Sun by 47 million kilometers, then moves away by 70 million kilometers. If we could observe the Sun from the surface of Mercury, then from there it would look three times larger than from Earth.
One year on Mercury is equal to 88 Earth days.
Mercury photo
We bring to your attention a photo of this planet.
Temperature on Mercury
What is the temperature on Mercury? Although this planet is located closest to the Sun, the championship of the warmest planet in the solar system belongs to its neighbor Venus, whose thick atmosphere, which literally envelops the planet, allows it to retain heat. As for Mercury, due to the absence of an atmosphere, its heat escapes and the planet both heats up quickly and cools down quickly, every day and every night there are simply huge temperature drops from +450 C during the day to -170 C at night. At the same time, the average temperature on Mercury will be 140 C, but this is not cold, not hot, the weather on Mercury leaves much to be desired.
Is there life on Mercury
As you probably guessed, with such temperature fluctuations, the existence of life is not possible.
Atmosphere of Mercury
We wrote above that there is no atmosphere on Mercury, although this statement can be argued, the atmosphere of the planet Mercury is not so absent, it is simply different and different from what we mean by the atmosphere itself.
The original atmosphere of this planet was dispersed 4.6 billion years ago due to the very weak Mercury, which simply could not hold it. In addition, proximity to the Sun and constant solar winds also did not contribute to the preservation of the atmosphere in the classical sense of the term. However, a faint atmosphere still exists on Mercury, and it is one of the most unstable and insignificant atmospheres in the solar system.
The composition of the atmosphere of Mercury includes helium, potassium, sodium, and also water vapor. In addition, the current atmosphere of the planet is periodically replenished from various diverse sources, such as solar wind particles, volcanic degassing, radioactive decay of elements.
Also, despite the small size and scanty density, the atmosphere of Mercury can be divided into as many as four sections: the lower, middle and upper layers, as well as the exosphere. The lower atmosphere contains a lot of dust, which gives Mercury a peculiar red-brown appearance, it warms up to high temperatures due to the heat that is reflected from the surface. The middle atmosphere has a jet similar to the earth's. The upper atmosphere of Mercury actively interacts with solar winds, which also heat it up to high temperatures.
The surface of the planet Mercury is a bare rock of volcanic origin. Billions of years ago, molten lava cooled and formed a rocky, gray surface. This surface is also responsible for the color of Mercury - dark gray, although due to dust in the lower layers of the atmosphere, one gets the feeling that Mercury is red-brown. Pictures of the surface of Mercury taken from the Messenger research probe are very reminiscent of the lunar landscape, the only thing is that there are no “lunar seas” on Mercury, while there are no Mercury scarps on the Moon.
Rings of Mercury
Does Mercury have rings? After all, many planets of the solar system, for example, and of course they are present. Alas, Mercury has no rings at all. Rings cannot exist on Mercury, again due to the proximity of this planet to the Sun, because the rings of other planets are formed from ice fragments, a piece of asteroids and other celestial objects, which near Mercury are simply melted by hot solar winds.
Moons of Mercury
Like the rings of satellites, Mercury does not have. This is due to the fact that not so many asteroids fly around this planet - potential satellite candidates when they come into contact with the planet's gravity.
Rotation of Mercury
The rotation of the planet Mercury is very unusual, namely, the orbital period of its rotation is shorter compared to the duration of rotation around its axis. This duration is less than 180 Earth days. While the orbital period is half that. In other words, Mercury goes through two orbits in its three revolutions.
How long is the flight to Mercury
At the closest point, the minimum distance from Earth to Mercury is 77.3 million kilometers. How long will it take modern spacecraft to overcome such a distance? NASA's fastest spacecraft to date, New Horizons, which was launched to Pluto, has a speed of about 80,000 kilometers per hour. It would take him about 40 days to fly to Mercury, which is relatively not so long.
The first spacecraft Mariner 10 launched to Mercury back in 1973 was not so fast, it took him 147 days to fly to this planet. Technology is improving, and perhaps in the near future it will be possible to fly to Mercury in a few hours.
- Mercury is not easy enough to spot in the sky, as it "likes to play hide-and-seek" by literally "hiding" behind the Sun. However, astronomers of antiquity knew about it. This is explained by the fact that in those distant times the sky was darker due to the lack of light pollution, and the planet was visible much better.
- The shift in Mercury's orbit helped confirm Albert Einstein's famous. In short, she tells how the light of a star changes when another planet revolves around it. Astronomers reflected a radar signal from Mercury, and the path of this signal coincided with predictions general theory relativity.
- The magnetic field of Mercury, the very existence of which is very mysterious, in addition to everything else, it also differs at the poles of the planet. On the south pole it is more intense than in the north.
Mercury- the planet closest to the Sun (you will find general information about Mercury and other planets in Appendix 1) - the average distance from the Sun is 57,909,176 km. However, the distance from the Sun to Mercury can vary from 46.08 to 68.86 million km. The distance of Mercury from the Earth is from 82 to 217 million km. Mercury's axis is almost perpendicular to the plane of its orbit.
Due to the slight inclination of the axis of rotation of Mercury to the plane of its orbit, there are no noticeable seasonal changes on this planet. Mercury has no satellites.
Mercury is a small planet. Its mass is a twentieth of the mass of the Earth, and the radius is 2.5 times less than the earth's.
Scientists believe that in the center of the planet there is a large iron core - it accounts for 80% of the mass of the planet, and on top - a mantle of stone rocks.
For observations from the Earth, Mercury is a difficult object, since it always has to be observed against the background of the evening or morning dawn low above the horizon, and besides, at this time, the observer sees only half of its disk illuminated.
The first to explore Mercury was the American space probe Mariner-10, which in 1974-1975. flew past the planet three times. The maximum approach of this space probe to Mercury was 320 km.
The surface of the planet looks like a wrinkled apple peel, it is pitted with cracks, depressions, mountain ranges, the highest of which reach 2-4 km, sheer ledges-escarps 2-3 km high and hundreds of kilometers long. In a number of regions of the planet, valleys and craterless plains are visible on the surface. Average density soil - 5.43 g / cm 3.
On the studied hemisphere of Mercury there is the only flat place - the Heat Plain. It is assumed that this is a frozen lava that erupted from the depths after a collision with a giant asteroid about 4 billion years ago.
Atmosphere of MercuryThe atmosphere of Mercury has an extremely low density. It consists of hydrogen, helium, oxygen, calcium vapor, sodium and potassium (Fig. 1). The planet probably receives hydrogen and helium from the Sun, and metals evaporate from its surface. This thin shell can be called "atmosphere" only with a big stretch. The pressure at the surface of the planet is 500 billion times less than at the surface of the Earth (this is less than in modern vacuum installations on Earth).
General characteristics of the planet Mercury
The maximum surface temperature of Mercury, recorded by sensors, is +410 °C. The average temperature of the night hemisphere is -162 ° C, and the daytime +347 ° C (this is enough to melt lead or tin). Temperature differences due to the change of seasons caused by the elongation of the orbit reach 100 °C on the day side. At a depth of 1 m, the temperature is constant and equal to +75 ° C, because porous soil does not conduct heat well.
Organic life on Mercury is ruled out.
Rice. 1. The composition of the atmosphere of Mercury
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 nature
The surface of Mercury (photo is given later in the article), taken by the Mariner-10 and Messenger probes, outwardly looked like the moon. The planet is largely dotted with craters of various sizes. The smallest visible in the most detailed photographs of the Mariner are 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, formed as a result of a collision, the Zhara Plain Basin (Caloris Planitia). When meeting with Mariner 10, only half of it was illuminated, and it was completely discovered by Messenger during its first flyby of the planet in January 2008.
craters
The most common structures of the planet's relief are craters. They cover the surface to a large extent (photos are given below) at first glance it looks like 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 high density of its huge core of iron and sulfur. The strong gravity tends to keep the material ejected from the crater close to the impact site. Compared to the Moon, it fell at only 65% of the lunar distance. This may be one of the factors that contributed to the formation of secondary craters on the planet, formed under the influence of ejected material, in contrast to the primary ones that arose directly from a collision with an asteroid or comet. The higher gravity means that the complex shapes and structures characteristic of large craters—central peaks, steep slopes, and flat bases—are observed on Mercury at smaller craters (minimum diameter about 10 km) than on the Moon (about 19 km). Structures smaller than these dimensions have simple cup-like outlines. Mercury's craters are different from those on Mars, although the two planets have comparable gravity. Fresh craters on the first are usually deeper than comparable formations on the second. This may be due to the low content of volatiles in Mercury's crust or higher impact velocities (because the speed of an object in solar orbit increases as it approaches the Sun).
Craters larger than 100 km in diameter begin to approach the oval shape characteristic of such large formations. These structures - polycyclic basins - are 300 km or more in size and are the result of the most powerful collisions. Several dozen of them were found on the photographed part of the planet. Messenger images and laser altimetry have greatly contributed to the understanding of these residual scars from the early asteroid bombardments of Mercury.
Heat Plain
This impact structure extends for 1550 km. When it was first discovered by Mariner 10, it was believed that its size was much smaller. The interior of the object is smooth plains covered with folded and broken concentric circles. The largest ranges stretch for several hundred kilometers in length, about 3 km in width and less than 300 meters in height. More than 200 breaks, comparable in size to the edges, emanate from the center of the plain; many of them are depressions bounded by furrows (grabens). Where grabens intersect with ridges, they tend to run through them, indicating their later formation.
Surface types
The Zhara Plain is surrounded by two types of terrain - its edge and relief formed by discarded rock. The edge is a ring of irregular mountain blocks reaching 3 km in height, which are the highest mountains found on the planet, with relatively steep slopes towards the center. The second much smaller ring is 100-150 km away from the first one. Behind the outer slopes is a zone of linear radial ridges and valleys, partially filled with plains, some of which are dotted with numerous hillocks and hills several hundred meters high. The origin of the formations that make up the wide rings around the Zhara basin is controversial. Some of the plains on the Moon were formed mainly as a result of the interaction of ejecta with the already existing surface topography, and this may also be true for Mercury. But the results of Messenger suggest that volcanic activity played a significant role in their formation. Not only are there few craters compared to the Zhara basin, indicating a long period of plains formation, but they have other features more clearly associated with volcanism than could be seen in the Mariner 10 images. Critical evidence for volcanism has come from Messenger images showing volcanic vents, many along the outer edge of the Zhara Plain.
Raditlady crater
Caloris is one of the youngest large polycyclic plains, at least in 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. The Messenger images revealed another, much smaller impact crater with a visible inner ring that may have formed much later, called the Raditlady Basin.
Strange antipode
On the other side of the planet, exactly 180° opposite the Zhara Plain, is a patch of strangely distorted terrain. Scientists interpret this fact by speaking of their simultaneous formation by focusing seismic waves from events that affected the antipodal surface of Mercury. The hilly and lined terrain is a vast zone of uplands, which are hilly polygons 5-10 km wide and up to 1.5 km high. The craters that existed before were turned 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, which indicates their later filling.
Plains
The plain is the relatively flat or gently undulating surface of Mercury, Venus, Earth, and Mars, and is found everywhere on these planets. It is a "canvas" on which the landscape developed. The plains are evidence of the process of destruction of the rough terrain and the creation of a flattened space.
There are at least three ways of "polishing" that probably flattened the surface of Mercury.
One way - increasing the temperature - reduces the strength of the bark and its ability to hold high relief. Over millions of years, the mountains "sink", the bottom of the craters will rise and the surface of Mercury will level out.
The second method involves the movement of rocks towards lower areas of the terrain 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 way is to hit fragments of rocks on the surface of Mercury from above, which ultimately leads to the alignment of the rough relief. An example of this mechanism is the ejection of rock during the formation of craters and volcanic ash.
Volcanic activity
Some evidence in favor of the hypothesis of the influence of volcanic activity on the formation of many plains surrounding the Zhara basin has already been presented. Other relatively young plains on Mercury, especially visible in regions lit from low angles during the first flyby of the Messenger, show characteristic features of volcanism. For example, several old craters were filled to the brim with lava flows, similar to the same formations on the Moon and Mars. However, the widespread plains on Mercury are more difficult to assess. Since they are older, it is clear that volcanoes and other volcanic formations may have eroded or otherwise collapsed, making them difficult to explain. Understanding these old plains has importance, since they are probably involved in the disappearance of most of the craters with a diameter of 10-30 km, compared with the Moon.
Escarps
The most important landforms of Mercury, which allow you to get 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 the height - 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 crack formation, when part of the soil rose and lay on the surrounding area. On Earth, such structures are limited in volume and arise under local horizontal compression in earth's crust. But the entire investigated surface of Mercury is covered with scarps, which means that the planet's crust has decreased in the past. From the number and geometry of scarps, it follows that the planet has decreased in diameter by 3 km.
In addition, shrinkage must have continued until relatively recently in geological history time, as some scarps have changed the shape of well-preserved (and therefore relatively young) impact craters. The slowdown of the initially high speed of the planet's rotation by tidal forces produced a compression in the equatorial latitudes of Mercury. The globally distributed scarps, however, suggest a different explanation: late mantle cooling, possibly combined with the solidification of part of the once completely molten core, led to core compression 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, suggesting that the compression process is incomplete.
The surface of Mercury: what is it made of?
Scientists tried to figure out the composition of the planet by examining sunlight reflected from different parts of it. One of the differences between Mercury and the Moon, besides the fact that the former is slightly darker, is that its surface brightness spectrum is smaller. For example, the seas of the Earth's satellite - smooth expanses visible to the naked eye as large dark spots - are much darker than the highlands dotted with craters, and the plains of Mercury are only slightly darker. The color differences on the planet are less pronounced, although the Messenger images taken with a set of color filters showed small very colorful areas associated with the vents of volcanoes. These features, plus the relatively inconspicuous visible and near-infrared spectrum of reflected sunlight, suggest that Mercury's surface is composed of iron- and titanium-poor, darker-colored silicate minerals than the lunar seas. In particular, the planet's rocks may be low in iron oxides (FeO), and this leads to the assumption that it was formed in much more reducing conditions (i.e., with a lack of oxygen) than other representatives of the terrestrial group.
Problems of remote research
It is very difficult to determine the composition of the planet by remote sensing of sunlight and the spectrum of thermal radiation that reflects the surface of Mercury. The planet heats up strongly, which changes the optical properties of mineral particles and complicates direct interpretation. However, the Messenger was equipped with several instruments that were not on board the Mariner 10, which measured the chemical and mineral composition directly. These instruments required a long period of observation while the craft remained close to Mercury, so there were no concrete results after the first three brief flybys. Only during the orbital mission of the Messenger did enough new information about the composition of the planet's surface appear.
A planet in the solar system whose orbit is within the Earth's orbit. The fact that Mercury is close to the Sun makes it virtually invisible to the naked eye. In fact, Mercury can be observed near the Sun 2 hours after sunset and 2 hours after sunrise.
Mercury is denoted by the symbol ☿.
Despite this, Mercury has been known since at least Sumerian times, about 5,000 years ago. In classical Greece he was called Apollo when he appeared as the morning star before sunrise and was called Hermes when he appeared as the evening star just after sunset.
Until the end of the 20th century, Mercury was one of the least studied planets, and even now we can talk about insufficient information about this planet.
So, for example, the length of its day, that is, the period of a complete revolution around its axis, was not determined until 1960.
Mercury is most comparable in size and relief shape with the Moon, but
Mercury is much denser, with a metallic core that makes up about 61% of its volume (compared to 4% for the Moon and 16% for the Earth).
The surface of Mercury differs from the lunar landscape in the absence of massive dark lava flows.
The proximity of Mercury to the Sun does not allow for full-fledged studies directly from the Earth. For a more in-depth study of the planet, the United States launched a spacecraft, which was given the name Messenger ("Messenger" - as indicated in the media).
The envoy was launched in 2004, flew past the planet in 2008, in 2009, entered the orbit of Mercury in 2011.
The proximity of Mercury to the Sun is used to study the theory of how gravity affects space and time.
The main characteristics of Mercury
Mercury is the closest planet to the Sun in the solar system.
The average orbital distance is 58 million km, it has the shortest duration of the year (an orbital period of 88 days) and receives the most intense solar radiation compared to all the planets.
Mercury is the smallest planet in the solar system, with a radius of 2440 km, it is smaller than Jupiter's largest moon, Ganymede, or Saturn's largest moon, Titan.
Mercury is an unusually dense planet, its average density is about the same as that of the Earth, but it has less mass and therefore is less compressed by its own gravity, adjusted for self-compression, the density of Mercury is the highest compared to any of the planets in the solar system.
Nearly two-thirds of Mercury's mass is contained in an iron core that extends from the planet's center with a radius of about 2100, or about 85% of its volume. The rocky outer shell of the planet - its crust and mantle layer have a thickness (depth) of only 300 km.
Problems of studying the planet Mercury
Mercury from Earth is never observed more than 28° in angular distance from the Sun.
The synodic period of Mercury is 116 days. Visible proximity to the horizon means that Mercury is always visible through the more turbulent currents of the Earth's atmosphere, which blur the visible image.
Even outside the atmosphere, orbiting observatories such as the Hubble Space Telescope require special setups and highly sensitive sensors to observe Mercury.
Because Mercury's orbit is within Earth's orbit, it occasionally passes directly between the Earth and the Sun. This event, when the planet can be observed as a small black dot that crosses the bright disk of the sun, is called a transit eclipse, this happens about a dozen times a century.
Mercury also makes it difficult for space probes to study. The planet is deep in the gravitational field of the Sun, a very large amount of energy is needed to form the trajectory of the spacecraft in order to enter the orbit of Mercury from the Earth.
The first spaceship, which approached Mercury was - Mariner 10, he made three short flights near the planet in 1974-75. But it was orbiting the Sun, not Mercury.
When developing follow-up missions to Mercury by the Messenger spacecraft in 2004, engineers had to calculate complex routes using gravity from repeated flybys of Venus and Mercury over several years. The point is also that thermal radiation comes not only from the Sun, but also from Mercury itself, thus, when developing spacecraft to study Mercury, it is necessary to develop a system of protection against thermal radiation.
Mercury and tests of the theory of relativity.
Mercury made it possible to conduct and once again prove the consistency of Einstein's theory of relativity. The bottom line is that mass should affect space and speed. The experiment was as follows. When the location of the Earth, Mercury and the Sun becomes such that between Mercury and the Earth is the Sun, but not in a straight line, but somewhat to the side. An electromagnetic signal is sent from Earth to Mercury, it is reflected from Mercury and comes back to Earth. Knowing the distance to Mercury at a given time and the speed of signal propagation, scientists came to the conclusion that the signal to Mercury went in curved space. The curvature of this space was influenced by the huge mass of the Sun, that is, the signal did not go along a conventional straight line, but deviated slightly towards the Sun. Thus, this was the second important confirmation of the theory of relativity.
Data from spacecraft Mariner 10, Messenger.
Mariner 10 flew close to Mercury three times, but Mariner 10 orbited the Sun? And not Mercury and its orbit partially coincided with the orbit of Mercury itself, in this regard, it was not possible to study 100% of the planet's surface, the pictures were taken on an area of about 45% of the entire surface of the planet. Mercury was found to have a magnetic field, and scientists did not expect that such a small planet and so slowly rotating would have such a powerful magnetic field. A spectral study has shown that Mercury has a very rarefied atmosphere.
First substantial post-mission telescopic surveys of Mercury Mariner 10 led to the discovery of sodium in its atmosphere, this happened in the mid-1980s. In addition, studies from more advanced ground-based radars have led to the creation of maps of the hemisphere, invisible Mariner 10 and in particular to the discovery of condensed material in craters near the poles, possibly ice.
In 2008 research Messenger, made it possible to obtain photographs of more than 1/3 of the planet's surface. The study took place within 200 km from the planet's surface and made it possible to consider many previously unknown geological features. In 2011 Messenger entered Mercury orbit and began research.
Mercury atmosphere
The planet is very small and hot, so there is little chance for Mercury to retain its atmosphere, even if it once existed. It should be noted that the pressure on the surface of Mercury is less than one trillionth of the pressure on the surface of the Earth.
However, the traces of atmospheric components that have been found have provided clues to planetary processes.
Mariner 10 detected a small number of helium atoms and an even smaller amount of atomic hydrogen near the surface of Mercury. These atoms are mainly formed from the solar wind, a stream of charged particles from the Sun, but these substances are constantly formed and constantly go back into the outer spaces. solar system. Perhaps the delay of the substance occurs no longer than a few hours.
Mariner 10 also detected atomic oxygen, which, along with the sodium, potassium and calcium subsequently detected by telescopic observations, is likely formed from the surface of Mercury's soil or from the impact of meteorites, and released into the atmosphere either by the impact or bombardment of solar wind particles.
Atmospheric gases, as a rule, accumulate on the night side of Mercury and are dispersed by the action of the Sun in the morning.
Many atoms are ionized by the solar wind and Mercury's magnetosphere. Unlike Mariner 10, the Messenger spacecraft has instruments that can detect ions. During the first flyby of the Messenger in 2008, ions of oxygen, sodium, magnesium, potassium, calcium and sulfur were detected. In addition, Mercury has a peculiar tail, which is detected when viewing sodium emission lines.
The idea that the planet closest to the Sun could have a significant amount of water ice initially seemed strange.
However, Mercury must have accumulated water over its entire history, for example from impacts from comets. Water ice on the hot surface of Mercury will immediately turn into steam, and individual water molecules will move in random directions, along a ballistic trajectory.
Calculations show that it is possible that 1 in 10 water molecules may eventually be concentrated in the polar regions of the planet.
Because Mercury's axis of rotation is essentially perpendicular to the plane of its orbit, sunlight at the poles strikes almost horizontally.
Under such conditions, the planet's poles are constantly in shadow and provide cold traps into which water molecules can fall for millions or billions of years. Gradually the polar ice will grow. But the reflected rays of the Sun, from the edges of the craters, will stop its growth, and it will be covered with dust and debris from the meteorite bombardment, let's say - garbage.
Radar data suggests that the reflective layer is indeed covered with a layer of 0.5 meters of such debris.
It is impossible to say with 100% certainty that the caps of Mercury are covered with ice or at least partially contained ice.
It can also be atomic sulfur, a very common substance in space.
Research on Mercury continues and new secrets of this planet will be revealed over time.
Mercury Features:
Weight: 03302 x10 24 kg
Volume: 6.083 x10 10 km 3
Radius: 2439.7 km
Average density: 5427 kg/m3
Gravity (ed ): 3.7 m/s
Free fall acceleration: 3.7 m/s
Second escape velocity: 4.3 km/s
Solar energy: 9126.6 W/m2
Distance from the Sun: 57.91x 10 6 km
Synodic period: 115.88 days
Maximum orbital speed: 58.98 km/s
Minimum orbital speed: 38.86 km/s
Orbital inclination: 7o
Period of rotation around its axis: 1407.6 hours
Daylength: 4226.6 hours
Tilt of the axis to the plane of the ecliptic: 0.01 o
Minimum distance to Earth: 77.3 x 10 6 km
Maximum distance to Earth: 221.9x 10 6 km
Average temperature on the illuminated side: +167 C
Average temperature on the shady side: -187 C
Dimensions of Mercury compared to Earth:
