Mysterious red planet

Since ancient times, the attention of people in the night sky has been attracted by a small red star. In our time, every day opens up new pages in the study of space and humanity can come to grips with the study of this distant world. The fourth planet farthest from the Sun is almost 10 times lighter than the Earth, its mass is slightly less than 11% of the Earth. Mars owes its name to the red tint given to its surface by iron oxide, thanks to this color the planet got the name of the god of war of the ancient Romans. Although Mars belongs to the terrestrial planets, it bears little resemblance to the Earth. A rarefied atmosphere (the pressure is about 160 times less than Earth's), a temperature range from -140°C to +20°C, a surface pitted with craters - an uncomfortable, but wonderful world!

The atmosphere of Mars is radically different from the Earth's both in composition and in physical parameters. The surface pressure is only 1/110 of Earth's. Mars, like Venus, has a very weak magnetic field, as a result of which the solar wind gradually blows the planet's atmosphere into space. Previously it was thought that martian atmosphere consists mainly of nitrogen and only in 1947 it was found that 95% of it is carbon dioxide. The average temperature at the surface of the planet is -45 degrees Celsius and decreases by 2.5 degrees per kilometer with increasing altitude.

For a long time Mars was considered as a spare home for mankind. But the reality turned out to be very harsh, which is worth only radiation on the surface of the planet. So apple trees on Mars will bloom very soon ...

Mars at present

Mars is now a cold, dry, and probably lifeless planet, but it wasn't always like this. In the distance, there was a sufficiently dense atmosphere and a large number of water. There were so many of her. that on the surface of the planet there were also lakes, as well as an extensive river system. But, unfortunately, gradually Mars lost its atmosphere due to the action of the solar wind and became what it is now.

The image was taken by the Viking 1 apparatus in 1976. On the left, the “smiling crater” of Halle is visible

Mars rover "Sojourner" near the rock "Yogi"

Solar panel of the "Phoenix" spacecraft and soil sampling device

Mars rover "Spirit" photographed its landing platform

Self-portrait "Curiosity"

Sunset at Gale Crater. Image taken by Curiosity on April 15, 2015, Sol 956 of the mission.

Sunrise on Mount Olympus as imagined by the Dutch artist Kees Venebos

Mount Arsia, an extinct shield volcano in the province of Tharsis

The question of whether there is life on Mars has haunted people for many decades. The mystery became even more relevant after suspicions arose about the presence of river valleys on the planet: if water streams once flowed through them, then the presence of life on a planet located next to the Earth cannot be denied.

Mars is located between the Earth and Jupiter, is the seventh largest planet in the solar system and the fourth largest from the Sun. The red planet is two times smaller than our Earth: its radius at the equator is almost 3.4 thousand km (the equatorial radius of Mars is twenty kilometers larger than the polar one).

From Jupiter, which is the fifth planet from the Sun, Mars is located at a distance of 486 to 612 million km. The Earth is much closer: the smallest distance between the planets is 56 million km, the largest distance is about 400 million km.
It is not surprising that Mars is very well distinguishable in the earth's sky. Only Jupiter and Venus are brighter than it, and even then not always: once every fifteen to seventeen years, when the red planet approaches the Earth at a minimum distance, for a crescent, Mars is the brightest object in the sky.

Named the fourth planet in order solar system in honor of the god of war ancient rome, therefore, the graphic symbol of Mars is a circle with an arrow, which is directed to the right and up (the circle symbolizes vitality, the arrow - a shield and a spear).

terrestrial planets

Mars, along with three other planets that are closest to the Sun, namely Mercury, Earth and Venus, is part of the terrestrial planets.

All four planets of this group are characterized by high density. Unlike the gas planets (Jupiter, Uranus), they consist of iron, silicon, oxygen, aluminum, magnesium and other heavy elements (for example, iron oxide gives the surface of Mars a red tint). At the same time, the terrestrial planets are much inferior in mass to the gas ones: the most major planet terrestrial group, the Earth, is fourteen times lighter than the lightest gas planet in our system - Uranus.

Like the rest of the terrestrial planets, Earth, Venus, Mercury, Mars is characterized by the following structure:

Inside the planet - a partially liquid iron core with a radius of 1480 to 1800 km, with a slight admixture of sulfur;
Silicate mantle;
The crust, consisting of various rocks, mainly basalt (the average thickness of the Martian crust is 50 km, the maximum is 125).

It is worth noting that the third and fourth terrestrial planets from the Sun have natural satellites. The Earth has one - the Moon, but Mars has two - Phobos and Deimos, which were named after the sons of the god Mars, but in the Greek interpretation, who always accompanied him in battle.

According to one hypothesis, the satellites are asteroids caught in the gravitational field of Mars, therefore the satellites are small in size and have an irregular shape. At the same time, Phobos gradually slows down its movement, as a result of which in the future it will either disintegrate or fall to Mars, but the second satellite, Deimos, on the contrary, is gradually moving away from the red planet.

one more interesting fact about Phobos is that, unlike Deimos and other satellites of the planets of the solar system, it rises from the western side and goes beyond the horizon in the east.

Relief

In earlier times, there was a movement of lithospheric plates on Mars, which caused the rise and fall of the Martian crust (tectonic plates are moving now, but not so actively). The relief is notable for the fact that despite the fact that Mars is one of the smallest planets, many of the largest objects in the solar system are located here:

Here is the most high mountain of those discovered on the planets of the solar system is the inactive volcano Olympus: its height from the base is 21.2 km. If you look at the map, you can see what surrounds the mountain great amount small hills and ridges.

Located on the red planet largest system canyons, known as the Mariner Valley: on the map of Mars, their length is about 4.5 thousand km, width - 200 km, depth -11 km.

The largest impact crater is located in the northern hemisphere of the planet: its diameter is about 10.5 thousand km, its width is 8.5 thousand km.

An interesting fact: the surface of the southern and northern hemispheres are very different. On the south side, the relief of the planet is slightly elevated and heavily dotted with craters.

The surface of the northern hemisphere, on the contrary, is below the average level. There are practically no craters on it, and therefore it is a smooth plain that was formed by flowing lava and erosion processes. Also in the northern hemisphere are areas of volcanic highlands, Elysium and Tharsis. The length of Tharsis on the map is about two thousand kilometers, and average height mountain system - about ten kilometers (here is the volcano Olympus).

The difference in relief between the hemispheres is not a smooth transition, but is a wide border along the entire circumference of the planet, which is located not on the equator, but thirty degrees from it, forming a slope in a northerly direction (along this border there are most of the eroded areas). At the moment, scientists explain this phenomenon in two ways:

At an early stage in the formation of the planet, the tectonic plates, being next to each other, converged in one hemisphere and froze;
The boundary appeared after the collision of the planet with a space object the size of Pluto.

Poles of the red planet

If you carefully look at the map of the planet of the god Mars, you can see that at both poles there are glaciers with an area of several thousand kilometers, consisting of water ice and frozen carbon dioxide, and their thickness ranges from one meter to four kilometers.

An interesting fact is that at the South Pole, the devices detected active geysers: in the spring, when the air temperature rises, fountains from carbon dioxide fly over the surface, kicking up sand and dust

Depending on the season, the polar caps change their shape every year: in spring, dry ice, bypassing the liquid phase, turns into vapor, and the exposed surface begins to darken. In winter, ice caps increase. At the same time, part of the territory, the area of which on the map is about a thousand kilometers, is constantly covered with ice.

Water

Until the middle of the last century, scientists believed that liquid water could be found on Mars, and this gave reason to say that life exists on the red planet. This theory was based on the fact that light and dark areas were clearly visible on the planet, which very much resembled seas and continents, and dark long lines on the map of the planet looked like river valleys.

But, after the very first flight to Mars, it became obvious that water, due to too low atmospheric pressure, cannot be in a liquid state on seventy percent of the planet. It is suggested that it did exist: this fact is evidenced by the found microscopic particles of the mineral hematite and other minerals, which usually form only in sedimentary rocks and are clearly amenable to water.

Also, many scientists are convinced that the dark stripes on the mountain heights are traces of the presence of liquid salt water at the present time: water flows appear at the end of summer and disappear at the beginning of winter.

The fact that this is water is evidenced by the fact that the stripes do not go over the obstacle, but flow around them, sometimes at the same time they diverge, and then merge again (they are very clearly visible on the map of the planet). Some features of the relief indicate that the riverbeds shifted during the gradual uplift of the surface and continued to flow in a direction convenient for them.

Another interesting fact that indicates the presence of water in the atmosphere is thick clouds, the appearance of which is associated with the fact that the uneven topography of the planet directs air masses upward, where they cool down, and the water vapor in them condenses into ice crystals.

Clouds appear over the Mariner canyons at an altitude of about 50 km, when Mars is at the point of perihelion. Air streams moving from the east stretch the clouds for several hundred kilometers, while at the same time their width is several tens.

Dark and light areas

Despite the absence of seas and oceans, the names assigned to the light and dark areas remained. If you look at the map, you can see that the seas are mostly located in the southern hemisphere, they are well visible and well studied.

But what are the dark areas on the map of Mars - this mystery has not been solved so far. Before the advent of spacecraft, it was believed that the dark areas were covered with vegetation. Now it has become obvious that in places where there are dark stripes and spots, the surface consists of hills, mountains, craters, with collisions of which air masses blow out dust. Therefore, the change in the size and shape of the spots is associated with the movement of dust, which has light or dark light.

Priming

Another evidence that in former times life existed on Mars, according to many scientists, is the soil of the planet, most of which consists of silica (25%), which, due to the content of iron in it, gives the soil a reddish tint. The soil of the planet contains a lot of calcium, magnesium, sulfur, sodium, aluminum. The ratio of soil acidity and some of its other characteristics are so close to those of the earth that plants could well take root on them, therefore, theoretically, life in such soil may well exist.

The presence of water ice was found in the soil (these facts were subsequently confirmed more than once). The mystery was finally solved in 2008, when one of the probes, staying at the north pole, was able to extract water from the soil. Five years later, information was released that the amount of water in the surface layers of the soil of Mars is about 2%.

Climate

The red planet rotates around its axis at an angle of 25.29 degrees. Due to this, the solar day here is 24 hours 39 minutes. 35 seconds, while the year on the planet of the god Mars, due to the elongation of the orbit, lasts 686.9 days.
The fourth planet in the solar system has seasons. True, the summer weather in the northern hemisphere is cold: summer begins when the planet is as far from the star as possible. But in the south it is hot and short: at this time, Mars approaches the star as close as possible.

Mars is characterized by cold weather. The average temperature of the planet is -50 ° C: in winter the temperature at the pole is -153 ° C, while at the equator in summer it is a little more than +22 ° C.

An important role in the distribution of temperature on Mars is played by numerous dust storms starting after the ice melts. At this time, atmospheric pressure rises rapidly, as a result of which large masses of gas begin to move towards the neighboring hemisphere at a speed of 10 to 100 m/s. At the same time, a huge amount of dust rises from the surface, which completely hides the relief (even the Olympus volcano is not visible).

Atmosphere

The thickness of the atmospheric layer of the planet is 110 km, and almost 96% of it consists of carbon dioxide (only 0.13% oxygen, slightly more nitrogen: 2.7%) and is very rarefied: the pressure of the atmosphere of the red planet is 160 times less than near the Earth, while due to the large difference in altitude, it fluctuates greatly.

Interestingly, in winter, about 20-30% of the entire atmosphere of the planet is concentrated and freezes to the poles, and during the melting of ice it returns to the atmosphere, bypassing the liquid state.

The surface of Mars is very poorly protected from the intrusion of celestial objects and waves from outside. According to one hypothesis, after a collision at an early stage of its existence with a large object, the impact was so strong that the rotation of the core stopped, and the planet lost most atmosphere and magnetic field, which acted as a shield, protecting her from intrusion celestial bodies and the solar wind, which carries radiation with it.

Therefore, when the Sun appears or goes below the horizon, the sky of Mars is reddish-pink, and a transition from blue to purple is noticeable near the solar disk. During the day, the sky is painted in a yellow-orange color, which gives it the reddish dust of the planet flying in a rarefied atmosphere.

At night, the brightest object in the sky of Mars is Venus, followed by Jupiter with satellites, in third place is the Earth (since our planet is located closer to the Sun, for Mars it is internal, therefore it is visible only in the morning or evening).

Is there life on Mars

The question of the existence of life on the red planet became especially popular after the publication of Wales' novel "War of the Worlds", according to the plot of which our planet was captured by humanoids, and earthlings only miraculously managed to survive. Since then, the secrets of the planet located between the Earth and Jupiter have been intriguing for more than one generation, and more and more people are interested in the description of Mars and its satellites.

If you look at a map of the solar system, it becomes obvious that Mars is at a short distance from us, therefore, if life could arise on Earth, then it could very well appear on Mars.

The intrigue is also fueled by scientists who report the presence of water on the terrestrial planet, as well as conditions suitable for the development of life in the composition of the soil. In addition, pictures are often published on the Internet and specialized magazines in which stones, shadows and other objects depicted on them are compared with buildings, monuments and even the remains of well-preserved representatives of local flora and fauna, trying to prove the existence of life on this planet and unravel all the secrets Mars.

Mars, the fourth of the terrestrial planets, is about half the size of the Earth (equatorial radius 3394 km) and nine times smaller in mass. The acceleration due to gravity on the surface of the planet is 376 cm/sec2. The angular diameter of Mars during the great oppositions is 25", during the aphelions 14". Stable details are observed on the surface of Mars, which made it possible to determine the period of its rotation with very high accuracy: 24h 37m 22s.6. The equator of the planet is inclined to the plane of its orbit by 24 ° 56 ", almost the same as that of the Earth. Therefore, on Mars there is a change of seasons, very similar to the earth, with the only difference being that the summer in the southern hemisphere of Mars is hotter and shorter, than in the north, since it occurs near the passage of the planet of its perihelion.The Martian year lasts 687 Earth days.

Details observed through a telescope on the disk of Mars can be classified as follows:

1. Bright regions, or continents, occupying 2/3 of the disk. They are uniform light fields of orange-reddish color.
2. Polar caps - white spots that form around the poles in autumn and disappear in early summer. These are the most noticeable details. In the middle of winter, the polar caps occupy the surface up to 50° in latitude. In summer, the northern polar cap disappears entirely, while a small remnant of the southern one remains. Through the blue filters, the polar caps stand out very contrastingly.
3. Dark areas (or seas) occupying 1/3 of the Disk. They are visible against the background of light areas in the form of spots, different in size and shape. Isolated dark areas of small size are called lakes or oases. Going into the continents, the seas form bays. Both the continents and the seas have a reddish color.

The ratio of the brightness of the continents and the seas is maximum in the red and infrared regions (up to 50% for the darkest seas), in the yellow and green rays it is less, in the blue on the disk of Mars the seas do not differ at all.

The dark regions, along with the polar caps, are involved in a cycle of periodic seasonal changes. In winter, dark areas have the least contrast. In spring, a dark fringe forms along the boundary of the polar cap, and the contrast of the dark areas around it increases. Darkening spreads gradually towards the equator, capturing more and more new areas. Many details that do not differ in this hemisphere in winter become clearly visible in summer. The darkening wave is propagating at a speed of about 30 km per day. In some areas, changes are repeated regularly from year to year, in others they occur differently every spring. In addition to recurring seasonal changes, the irreversible disappearance and appearance of dark details (secular changes) has been repeatedly observed. Light areas do not participate in the seasonal cycle, but may experience irreversible secular changes.

4. Clouds - temporary details localized in the atmosphere. Sometimes they cover a significant part of the disk, preventing the observation of dark regions. There are two types of clouds: yellow clouds, reputedly dust clouds (there are cases when yellow clouds cover the entire disk for whole months; such phenomena are called "dust storms"); white clouds, most likely consisting of ice crystals, like terrestrial cirruses.

AT last years The study of Mars has advanced greatly thanks to the use of automatic interplanetary stations. The American AMS "Mariner 4" first photographed Mars from a close distance (about 10,000 km) in 1965.

It turned out that Mars, like the Moon, is covered with craters. Mariner-4 flew near Mars and photographed it Mariner-6 and Mariner-7, and in 1971, a few months after the great confrontation, its first artificial satellites made by the hands of earthlings went into orbit around Mars : two Soviet ("Mars-2" and "Mars-3") and one American ("Mariner-9"). Their programs differed significantly and mutually complemented each other. The American satellite was aimed mainly at photographing Mars; he obtained several thousand photographs with a resolution of about 1 km, covering almost the entire surface of Mars.

Soviet satellites carried out photography in a much smaller volume, but they were equipped with a large amount of equipment designed to study the surface of Mars, its atmosphere and circumplanetary space. physical methods. The temperature of the surface layer was measured with an infrared radiometer and, simultaneously, with a radio telescope, the temperature of the soil at a depth of several tens of centimeters; measured the brightness at different wavelengths, atmospheric pressure and heights by the intensity of CO2 bands, the content of H2O in the atmosphere, the magnetic field, the composition and temperature of the upper atmosphere, the electron density in the ionosphere, and the behavior of interplanetary matter in the vicinity of Mars.

A descent vehicle separated from AMS "Mars-3", which made the first soft landing on the surface of Mars. The Soviet program for the exploration of Mars with the help of spacecraft received further development in 1974, when four Soviet spacecraft arrived at the planet. One of them, "Mars-6" landed on the surface, and during the descent in the atmosphere for the first time made direct measurements of its composition, temperature and pressure. "Mars-5" entered the orbit of an artificial satellite of the planet, and "Mars-4" and "Mars-7" carried out studies of the planet and interplanetary space on flyby trajectories.

Photographs of the surface taken from the Mariner-9, Mars-4 and Mars-5 showed that the surface of Mars is very diverse in the nature of geological forms. Most of it is covered with craters, but there are also flat areas almost devoid of craters. Among the craters come across those that are located on the tops of huge cone-shaped mountains. This arrangement means that these are not meteorite craters, but volcanic ones. On the slopes largest volcanoes there are few meteorite craters and, therefore, these volcanoes are "young", they formed relatively recently. Thus, Mars is a geologically active planet. Mars apparently has its own magnetic field, although much weaker than the Earth; the existence of its own magnetic field indicates the presence of a liquid core in the center of the planet.

On the surface of Mars there are formations that are very similar to dried up riverbeds. On July 20, 1976, the American descent vehicle Viking-1 landed on the surface of Mars.

The Martian landscape is very reminiscent of some terrestrial deserts. You can see sloping sand dunes, many angular stones.

The map of Mars shows the track along which measurements were taken during this passage. Devices "saw" first Southern Hemisphere Mars and in half an hour their optical axes crossed the entire planet from south to north. It can be seen that darker regions are also warmer (they absorb more solar heat).

In the northern regions (latitude j > 45°) the temperature drops to very low level, about 150 °K. Here is the polar cap zone. It manifests itself as a sharp increase in brightness in ultraviolet rays(0.37 microns), but not visible at all in the near infrared region (1.38 microns; here the planet still shines by reflection, and not by thermal radiation). This means that we see in this case not snow or ice on the surface, but clouds (of fine crystals) floating in the atmosphere. The size of the crystals is so small that at a wavelength of about 1 micron they no longer scatter light. It is possible that these are ordinary H2O ice crystals: we see how the content of H2O vapor drops sharply here. It should go into the solid phase. At these temperatures, carbon dioxide can also condense.

The surface temperature of Mars varies widely. At the equator during the day it reaches +30 °C, and at night -100 °C. This is due to the low thermal conductivity of the Martian soil. It is almost as low as that of the moon.

The most low temperature occurs in winter on the surface of the polar caps (-125°C).

In the spectrum of Mars, clearly visible CO2 bands are observed, although they are weaker than in the spectrum of Venus (see Fig. 166). Clouds on Mars usually cover a small fraction of the surface (unlike on Venus), and therefore the absolute value of the CO2 content in the atmosphere can be determined from spectroscopic observations. Since the intensity of weak and strong lines is affected differently by the total pressure of the gas, it can also be determined. The equipment installed on Mars-6 and Viking-1 and 2 measured the pressure in the Martian atmosphere directly using barometric sensors. It is equal to the surface on average 6 mb. Direct measurements were taken on Viking 1 and 2 chemical composition by using. mass spectrometer, which showed that the atmosphere of Mars is 95% CO2.

The pressure in different regions of Mars can differ several times due to the difference in altitudes. Most high areas Mars lie 20 km above the lowest.

Interestingly, dark and light areas are equally likely to be low and high. The northern hemisphere is dominated by low regions.

Water vapor lines have been found in the spectrum of Mars. In terrestrial observations, they can be separated from the earth lines only due to the Doppler shift, since they are very weak. In observations from spacecraft, this difficulty is absent. An example of observations from a spacecraft was given above.

The content of water vapor in the atmosphere of Mars varies over time and is different in different regions. Sometimes it is below the detection limit (about 1 micron of precipitated water for measurements made on Mars-3), sometimes it reaches 50 microns. This is the thickness of the film of water that would cover the planet if all of it were condensed. atmospheric water vapor. On Earth, the atmosphere contains about 1000 times more water. The average temperature of Mars (200 °K) is noticeably lower than the Earth's, and a layer of permafrost should be expected under its surface, which delays the release of H2O from the bowels of the planet.

Note that water cannot exist in the liquid phase at Martian temperatures and pressures; it can only be in the form of ice or steam.

In addition to H2O, some other small components were found in the atmosphere of Mars - N2 (2.5%), Ar (1.5%), CO (~0.01%), O2 (~0.01%), traces of ozone O3. The polar caps of Mars have a complex nature. Only at the edges and only at certain specific times are clouds. A significant part of the visible polar cap is a solid sediment on the surface, and this sediment is formed by frozen carbon dioxide with an admixture of ordinary water ice. In the polar caps (mainly in the non-disappearing completely southern one) contains more CO2 and H2O than in the atmosphere. The following very interesting suggestion has been made.

Due to the precession of the polar axis of Mars, once every 50,000 years, it turns out that both polar caps disappear completely and then the pressure in the atmosphere rises, the content of H2O increases, and liquid appears. water. Perhaps, during these periods, a river flowed, leaving the channel.

During the flight of American and Soviet space stations near Mars, experiments were carried out on the transmission of its atmosphere by radio waves, the same as in the study of Venus. They made it possible to determine atmospheric pressure and temperature at altitude.< 40 км и, кроме того, электронную концентрацию в ионосфере планеты. Максимум ионизации был найден на высоте 120 км, где электронная концентрация на дневной стороне планеты равна 105 см -3, т.е. на порядок меньше, чем в земной ионосфере.

Now that we have outlined the main observational data on the Martian surface and atmosphere, let us consider possible explanations for the periodic seasonal changes in the dark regions associated in time with the melting of the polar cap. One of them is that in spring, when the sublimation of the polar caps begins, the soil thaws, and humidity increases. Over time, this thawing process spreads further towards the equator, causing the darkening of the seas and oases. If the darkening processes are associated with an increase in soil moisture, then there are two possibilities:

1) dark areas are occupied by vegetation, which, like the earth, enters an active phase with the onset of spring due to an increase in temperature and humidity;
2) dark areas are covered with some kind of mineral material that darkens with increasing temperature or humidity.

However, the periodic darkening process may not be related to moisture at all. For example, it can be caused by periodic seasonal changes in wind directions. In the spring, the wind carries away smaller particles from the sea areas, and the seas darken; in the fall, small particles move in the opposite direction.

The ability of dark areas to recover has long been noted. There are often dust storms on Mars, which, it would seem, should have covered the seas long ago.

Nothing like that happens. Shortly after the end of the dust storm, the contrast of the dark areas is fully restored. This property is easily explained if we assume that the dark areas are covered with vegetation. But again, if we accept that the seas are areas from which smaller particles are easily blown away by the wind, the restoration of contrast can be explained without resorting to the vegetation hypothesis.

So, the phenomena that can be considered as an indication of the activity of the Martian biosphere are:

1) periodic seasonal changes in dark areas;
2) the relationship of periodic seasonal changes in dark areas with the sublimation of the polar caps;
3) the ability of dark areas to regenerate (contrast restoration).

All of them, as we have seen, may have an explanation very far from biological processes. Low atmospheric pressure and huge diurnal temperature fluctuations (not less than 100°) make many researchers take a negative view of the possibility of the existence of a biosphere on Mars. On the other hand, the enormous adaptability of living organisms is also known. Microorganisms are found in soil anaerobic bacteria) capable of carrying low pressures and temperature and do not need oxygen. Therefore, the search for living organisms on Mars does not seem completely hopeless. Such searches will apparently be carried out with the help of AMS capable of soft landing on the Martian surface.

Mars has two satellites, Phobos and Deimos, which were discovered by the American astronomer Hall in 1877. They are very close to the planet and are faint (+11m.5 and +12m.5), so it is difficult to observe them. Phobos is at a distance of 2.77 planetary radii from its center and its period of revolution is 7h 39m 14s, i.e. much less than the rotation period of Mars. As a result, Phobos rises in the west, despite the fact that the direction of its circulation is direct. Deimos revolves at an average distance of 6.96 planetary radii, with a period of 30h 17m 55s. On fig. 177 shows a photograph of Phobos taken from Mariner 9. Its surface is much more heavily cratered than the Martian, due to total absence atmospheric erosion. Both satellites are irregularly shaped. Phobos is about 22-25 km across, Deimos is about 13 km.

The four terrestrial planets have much in common in their characteristics. Almost all matter is concentrated in the lithosphere. The masses are in the range from 1.510-7 to 3; 10-6 M¤ and radii from approximately 3.510-3 to 9.0 × 10-3 R¤. Average densities lie in even narrower limits - from 4.0 (Mars) to 5.4-5.5 g/cm3 (the other three planets). Apparently, in the bowels of all the planets of this group there is a chemical differentiation: heavy elements (in particular, Fe) are concentrated towards the center, light and at the same time more fusible - in the outer shells; the crust and mantle are composed of silicate rocks. Perhaps all four planets have a liquid core. By at least Two planets (Earth and Mars) have volcanoes. On the surface of all four planets there are traces of tectonic activity (mountain building processes) on one scale or another.

All were subjected to a strong meteorite bombardment, which was one of the main factors in the formation of the surface of Mars and Mercury. On Earth, meteorite craters are almost completely erased by tectonic and erosional processes; on Venus, they are apparently much better preserved. The only energy source that determines the temperature and climate of the terrestrial planets is solar radiation. The flux of internal heat is negligible compared to the flux of solar radiation.

Three out of four planets have an atmosphere. Venus and Mars are similar in atmospheric composition: carbon dioxide is the main component in both cases, but its quantities are very different. The composition of the earth's atmosphere is completely different: there is very little nitrogen, oxygen, carbon dioxide, and, in addition, the Earth has a hydrosphere - a huge amount of water (which, on the contrary, is very small on Venus and Mars). The differences are big, but there are very important ones. common features: light gases - hydrogen and helium, the most abundant elements (which are part of the Sun, stars and interstellar gas) are present only as small components; all gases that are the main components of the atmosphere - (CO2, N2) and water are the products of gas release from volcanoes. Oxygen on Earth is a secondary product that has arisen from the decomposition of H2O as a result of photochemical and biological processes. The modern atmospheres of the terrestrial planets (and the Earth's hydrosphere) are definitely of secondary origin - in the sense that they were released by the lithosphere after it was formed.

The primordial atmosphere, which consisted mainly of light gases left over from a protoplanetary nebula, could have survived (if such an atmosphere existed at all) only for a very long time. a short time and had to dissipate quickly.

The amount of CO2 and N2 released during the existence of the planets (5109 years) is approximately the same on Earth and on Venus, and water, apparently, was released much more on Earth. liquid water dissolves CO2 very well and transforms into carbonate rocks. As a result, the hydrosphere on Earth removed almost all carbon dioxide, but on Venus it was not formed, and CO2 remained completely in the atmosphere. On Mars, the total rate of gas release is apparently two orders of magnitude lower than on Venus, and, in addition, the main part of the released amount of CO2 and H2O is bound in the polar caps and in the soil (as a result of adsorption and permafrost formation).

Almost completely devoid of the atmosphere of Mercury. Meanwhile, the acceleration of gravity on its surface is almost the same as that of Mars, and it could probably retain CO2 if it accumulated as much as on Mars. Much in the processes of formation and evolution of planetary atmospheres is not yet understood, this is one of interesting problems planetary physics, the development of which is just beginning.

Note that it has a certain practical significance, since it should predict the further evolution of the Earth's atmosphere and climate.

The orbit of Mars is elongated, so the distance to the Sun changes during the year by 21 million km. The distance to the Earth is also not constant. During the Great opposition of the planets, which occur once every 15-17 years, when the Sun, Earth and Mars line up, Mars approaches the Earth as close as 50-60 million km. The last Great Confrontation was in 2003. The maximum distance of Mars from the Earth reaches 400 million km.

A year on Mars is almost twice as long as an Earth year - 687 Earth days. The axis is inclined to the orbit - 65 °, which leads to a change in seasons. The period of rotation around its axis is 24.62 hours, i.e., only 41 minutes more than the period of rotation of the Earth. The tilt of the equator to the orbit is almost like that of the Earth. This means that the change of day and night and the change of seasons on Mars proceeds in much the same way as on Earth.

According to calculations, the core of Mars has a mass of up to 9% of the mass of the planet. It consists of iron and its alloys and is in a liquid state. Mars has a thick crust 100 km thick. Between them is a silicate mantle enriched in iron. The red color of Mars is precisely due to the fact that half of its soil consists of iron oxides. The planet seemed to be "rusted".

The sky over Mars is dark purple, and bright stars visible even during the day in calm, calm weather. The atmosphere has the following composition (Fig. 46): carbon dioxide - 95%, nitrogen - 2.5, atomic hydrogen, argon - 1.6%, the rest - water vapor, oxygen. In winter, carbon dioxide freezes, turning into dry ice. There are rare clouds in the atmosphere, and fogs over lowlands and at the bottom of craters in the cold season.

Rice. 46. The composition of the atmosphere of Mars

The average pressure of the atmosphere at the surface level is about 6.1 mbar. This is 15,000 times less than at and 160 times less than at the surface of the Earth. In the deepest depressions, the pressure reaches 12 mbar. The atmosphere of Mars is very thin. Mars is a cold planet. The lowest recorded temperature on Mars is -139°C. The planet is characterized by a sharp temperature drop. The temperature range can be 75-60 °C. On Mars there is climatic zones similar to those on earth. In the equatorial belt at noon the temperature rises to +20-25 °С, and at night it drops to -40 °С. In the temperate zone in the morning the temperature is 50-80 °C.

It is believed that a few billion years ago, Mars had an atmosphere with a density of 1-3 bar. At this pressure, water should be in a liquid state, and carbon dioxide should evaporate, and a greenhouse effect could occur (as on Venus). However, Mars was gradually losing its atmosphere due to its low mass. The greenhouse effect has been decreasing permafrost and polar caps, which are observed to this day.

Mars is home to the highest volcano in the solar system, Mount Olympus. Its height is 27,400 m, and the diameter of the base of the volcano reaches 600 km. This is an extinct volcano, which most likely spewed lava about 1.5 billion years ago.

General characteristics of the planet Mars

Currently, no active volcano has been found on Mars. Near Olympus there are other giant volcanoes: Mount Askrian, Mount Pavlina and Mount Arsia, whose height exceeds 20 km. The lava flowing out of them, before hardening, spread in all directions, so volcanoes are shaped more like cakes than cones. There are sand dunes on Mars, giant canyons and faults, as well as meteorite craters. The most grandiose canyon system is the Mariner Valley, 4,000 km long. In the past, rivers could flow on Mars, which left the channels that are currently observed.

In 1965, the American probe Mariner 4 transmitted the first images of Mars. The first Mars map. And in 1997, an American spacecraft delivered a robot to Mars - a six-wheeled cart 30 cm long and weighing 11 kg. The robot was on Mars from July 4 to September 27, 1997, studying this planet. Programs about his movement were broadcast on television and on the Internet.

Mars has two moons, Deimos and Phobos.

The assumption that Mars has two satellites was expressed in 1610 by a German mathematician, astronomer, physicist and astrologer Johannes Kepler (1571 — 1630), who discovered the laws of planetary motion.

However, the satellites of Mars were discovered only in 1877 by an American astrologer Asaph Hall (1829-1907).

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Detail:

The planet Mars

The main characteristics of Mars

Atmosphere of Mars

The composition and other parameters of the Martian atmosphere have been determined quite accurately by now. The atmosphere of Mars is composed of carbon dioxide (96%), nitrogen (2.7%) and argon (1.6%). Oxygen is present in negligible amounts (0.13%). Water vapor is presented as traces (0.03%). The pressure at the surface is only 0.006 (six thousandths) of the pressure at the Earth's surface. Martian clouds are made up of water vapor and carbon dioxide and look something like cirrus clouds above the Earth.

The color of the Martian sky is reddish due to the presence of dust in the air. Extremely rarefied air does not transfer heat well, so there is a large temperature difference in different parts of the planet.

Despite the rarefaction of the atmosphere, its lower layers represent a rather serious obstacle for spacecraft. So, the conical protective shells of the descent vehicles "Mariner-9"(1971) during the passage of the Martian atmosphere from its uppermost layers to a distance of 5 km from the surface of the planet, they were heated to a temperature of 1500 ° C. The Martian ionosphere extends from 110 to 130 km above the surface of the planet.

On the movement of Mars

Mars can be seen from Earth with the naked eye. Its apparent stellar magnitude reaches −2.9m (at its closest approach to the Earth), second only to Venus, the Moon and the Sun in brightness, but most of the time Jupiter is brighter than Mars for an earthly observer. Mars moves around the Sun in an elliptical orbit, then moving away from the star at 249.1 million km, then approaching it up to a distance of 206.7 million km.

If you carefully observe the movement of Mars, you can see that during the year the direction of its movement across the sky changes. By the way, ancient observers noticed this. At a certain point, it seems that Mars is moving in the opposite direction. But this movement is only apparent from the Earth. Mars, of course, cannot perform any reverse movement in its orbit. And the visibility of the reverse movement is created because the orbit of Mars is external in relation to the orbit of the Earth, and the average speed of movement in orbit around the Sun is higher for the Earth (29.79 km / s) than for Mars (24.1 km / s). At the moment when the Earth begins to overtake Mars in its movement around the Sun, and it seems that Mars began the reverse or, as astronomers call it, retrograde motion. The diagram of the reverse (retrograde) movement illustrates this phenomenon well.

The main characteristics of Mars

Name of parameters	Quantitative indicators
Average distance to the Sun	227.9 million km
Minimum distance to the Sun	206.7 million km
Maximum distance to the Sun	249.1 million km
Equator diameter	6786 km (Mars is almost half the size of the Earth in size - its equatorial diameter is ~ 53% of the Earth's)
Average orbital speed around the Sun	24.1 km/s
Period of rotation around its own axis (Sidereal equatorial period of rotation)	24h 37 min 22.6 s
Period of revolution around the sun	687 days
Known natural satellites	2
Mass (Earth = 1)	0.108 (6.418 × 10 23 kg)
Volume (Earth = 1)	0,15
Average density	3.9 g/cm³
Average surface temperature	minus 50°C (temperature difference is from -153°C at the pole in winter and up to +20°C at the equator at noon)
Axis Tilt	25°11"
Orbital inclination with respect to the ecliptic	1°9"
Surface pressure (Earth = 1)	0,006
Composition of the atmosphere	CO 2 - 96%, N - 2.7%, Ar - 1.6%, O 2 - 0.13%, H 2 O (vapors) - 0.03%
Acceleration of free fall at the equator	3.711 m/s² (0.378 Earth)
parabolic speed	5.0 km/s (for Earth 11.2 km/s)

It can be seen from the table which high precision the main parameters of the planet Mars are determined. This is not surprising if one bears in mind that the most modern scientific methods and high-precision equipment are now used for astronomical observations and research. But with a completely different feeling we relate to such facts from the history of science, when scientists of past centuries, who often did not have at their disposal any astronomical instruments, except for the most simple telescopes with a slight increase (maximum 15-20 times), made accurate astronomical calculations and even discovered the laws of motion of celestial bodies.

For example, let's recall that the Italian astronomer Giandomenico Cassini already in 1666 (!) determined the time of rotation of the planet Mars around its axis. His calculations gave a result of 24 hours and 40 minutes. Compare this result with the period of rotation of Mars around its axis, determined with the help of modern technical means (24 hours 37 minutes 23 seconds). Are our comments needed here?

Or such an example. at the very beginning of the 17th century, he discovered the laws of planetary motion, having neither precise astronomical instruments nor a mathematical apparatus for calculating the areas of such geometric figures as an ellipse and an oval. Suffering from a visual defect, he made the most accurate astronomical measurements.

Similar examples show great importance activity and enthusiasm in science, as well as devotion to the cause that a person serves.

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