Among the objects of the solar system, Mars continues to be the most curious and most explored planet. For all the time of close study by man of our near space, only the fourth planet of the solar system has received such attention. The reason for such an increased interest in our neighbor lies not only in its relative proximity to our world. The red planet is of interest to humanity in terms of the possibility of exploring extraterrestrial space.
The data that is available today about Mercury and Venus indicate that these are alien, hostile worlds for us. For these planets, nature has prepared the fate of physical and chemical laboratories. Mars, in many respects, is no longer so gloomy and lifeless. It is not for nothing that the literary laurels of the birthplace of the first extraterrestrial civilization belong to this planet. Why is Mars so interesting to us? What is a person really dealing with, turning his gaze to a small, reddish star in the night sky.
Description of the red planet
Of the entire list of planets in the solar system, Mars is perhaps the only space object that a person can fly to today. It is the second closest planet to us in the solar system. Even the level of technological development that human civilization has reached makes it possible to make plans for the exploration of Mars and the implementation of a manned flight to the fourth planet of our star system. Approximately for the implementation of this large-scale and grandiose program, it will take another 10-15 years. However, if we compare the preparatory measures now under way in this direction with the program for a visit by man to the Moon, the difference is obvious.
According to many data obtained recently with the help of automatic space probes and rovers, it is possible that life could have existed on the red planet millions of years ago. Not without reason, studying the obtained images of the surface of the planet Mars, scientists of all stripes are unanimous in their opinion - our neighbor is not hopeless. There are all prerequisites to believe that the fourth planet could be another oasis of life in our solar system. This is facilitated by the astrophysical parameters of the planet, data on the Martian atmosphere, and the climatic pattern on the surface of our neighbor.
In addition, if the Martian poles are covered with ice caps, the version about the presence of liquid water in the bowels of the planet has the right to life. If it is proved that liquid water has every chance of being in the nature of the red planet, then the question of finding life forms in this harsh place is just a matter of time.
Confidence to supporters of the usefulness of Mars for human exploration is given by information about the composition of the Martian air and astrophysical parameters similar to those of the Earth. Even under the condition that the atmosphere of the planet is far in its composition from the earth's air gap, we can talk about relatively acceptable conditions. A highly rarefied atmosphere does not inspire optimism, but to some extent it is better than the picture that we observe on Mercury or on hot Venus. Scientists believe that according to climatic parameters on Mars, the weather is quite tolerable. Severe frosts with temperatures down to -170°C in the polar regions give way to tropical heat in the equatorial regions. In summer days the temperature reaches +20°C. However, in winter, and especially at night, the temperature can drop to -125°C.
In other words, with the appropriate technical and physical training of a person, the Martian environment can be habitable. Do not discount the fact that such climatic conditions were the result of a cosmic cataclysm. It is possible that in the distant past of the planet, the climate on the planet was warmer and Martian life was rampant on the planet. This cannot be said in relation to other planets of the terrestrial group, where the slightest hints of the existence of conditions for the origin of life are completely absent.
The information that has been collected by the scientific community today gives every reason to consider the Red Planet as a convenient springboard for subsequent space exploration. Numerous works of scientists, flights of automatic probes to the planet and delivery of rovers to Mars made it possible to obtain a lot of useful information. We now know almost everything about the Martian soil, we have an idea of the most severe dust storms. Scientists have obtained detailed images of almost the entire surface of the planet, including the northern and southern polar caps. It remains only to process the tons of information received and draw the appropriate conclusions.
Brief description and features of the planet
From the point of view of academic science, Mars is a pronounced terrestrial planet. The slightly elongated orbit of the planet is located 1.5 times farther from the Sun than the orbit of the Earth. At perihelion, Mars moves away from our star at a distance of 250 million km, and at aphelion, the planet Mars is separated from the Sun by a distance of 207 million km. The Red Planet is twice the size of our Earth. The diameter of the fourth planet is 6,779 km, against 12,742 km. Earth's diameter.
If Mars is only twice as large as Earth, then the mass of the Red Planet is ten times lighter than our blue beauty, 6.39E23 kg versus 5.972E24 kg. Accordingly, the free fall acceleration of our neighbor is only 3.72 m/s2 against 9.807 m/s2. For all its miniature size, the relief of the planet is quite diverse. The Red Planet has mountains and valleys, vast depressions, deep canyons, and even meteorite craters similar to moon formations. Extinct volcanoes have been discovered on the surface of our neighbor, testifying to the turbulent youth of Mars. Here is the highest volcano in the solar system - Mount Olympus. Its top rests against the Martian sky, reaching 26 kilometers in height. This extinct volcano holds the record, with a height of 2.5 times the relative height of the terrestrial volcano Mauna Kea.
However, despite the varied terrain, the landscape on Mars is rather boring and monotonous. Mountain ranges are replaced by endless rocky deserts. The bright areas on the surface of the planet are called the continents, while the dark areas are the Martian seas. These elements of the Martian relief occupy more than 70% of the area of the southern hemisphere of Mars.
With all the monotony of the Martian surface, the planet has its own feature. Both hemispheres of Mars differ significantly both in morphological features and in terms of the intensity of external influence. In the northern hemisphere, the relief is dominated by valleys and smooth plains, although the surface of the planet in this part is below average. The southern hemisphere is dominated by meteorite craters and the surface itself is elevated. This fact to some extent explains the presence of tectonic plates that moved in ancient times. The dull Martian landscape is brightened up only by the polar caps available at the north and south poles of the planet.
Like all terrestrial planets, Mars has a classical structure:
- crust, 100 km thick at the poles and 8 km thick in the equatorial region in the region of the Hellas depression;
- an intermediate layer consisting of semi-liquid rocks;
- silicate mantle 1300-1500 km thick;
- an iron core with a diameter of 2960 km, which is half liquid.
The Red Planet has its own atmosphere. Its composition is dominated by carbon dioxide. To a lesser extent, the air mass of the planet contains nitrogen, hydrogen and oxygen. The presence of water vapor is very limited. Due to the strong rarefaction, the atmospheric pressure on Mars is 150 times less than the earth's pressure, only 6.1 millibars. The thickness of the gaseous shell around the planet is 110 km.
Assessing the physical information about the planet, it is worth paying attention to the astrophysical parameters of Mars, which are in many respects similar to the terrestrial parameters. The fourth planet makes a complete revolution around our star in 687 Earth days. At the same time, the speed of rotation of the red planet around its own axis is almost equal to the speed of rotation of the Earth - 24 hours and 37 minutes. In other words, time on the planet looks the same as on Earth. Due to its tilt and speed of rotation, Mars has a change of seasons, which is quite rare for other planets in the solar system. The length of the seasons on the surface of our neighbor is different. In the northern hemisphere, summer lasts 177 Martian days, while in the southern hemisphere, summer is 21 days shorter.
Brief description and nature of exploration of Mars
Since the first flights into space, man has not abandoned attempts to start studying neighboring planets. The first to head to the Red Planet was the American space probe Mariner 4, which for the first time photographed Mars from a close distance, flying past the planet. Subsequent missions were already more thorough and applied in nature. The American probe "Mariner-9" having reached the fourth planet, became its first artificial satellite. In 1971, the first ever landing on Mars was made by the Soviet AMS "Mars-3". Despite a successful landing, the Soviet apparatus lived only 14 seconds. Subsequent attempts to land on Mars ended in failure.
Only the American AMS "Viking-1" once again managed to make a soft landing on the planet and provide man with the first pictures of the surface of Mars. During the same expedition, the Martian soil samples were taken for the first time and data on the composition of the soil were obtained. Further, with enviable regularity, Soviet and American spacecraft, automatic probes of space agencies of different countries, including China, Japan and the European Community, were sent to the fourth planet. Over the next 45 years from the moment of the first flight of Mariner-4 towards Mars, 48 expeditions to the Red Planet were organized from the Earth. Of this number, almost half of the missions ended in failures.
To date, the following devices continue to explore the planet:
- the orbital satellite of Mars - the American apparatus "Mars-Odyssey";
- from the planet's orbit, the automatic probe of the European Space Agency "Mars-Express";
- American orbiter "Maven" and a satellite of the military department;
- the Indian orbital probe "Mangalyan" and the space probe "Trace Gas Orbiter" of ESA and Roscosmos.
Directly on the planet, two American rovers Opportunity and Curiosity continue to work, which have already become legendary creations of human thought. Numerous space probes, automatic Martian stations and rovers - all this equipment is an arsenal thrown by the scientific community to study the red planet.
Permanent satellites of Mars
Mars, despite its size, has two natural satellites - Phobos and Deimos, triaxial ellipsoids with dimensions of 26.8 × 22.4 × 18.4 km and 15 × 12.2 × 10.4 km, respectively.
The exact origin of these celestial bodies is unknown. The size of the Martian satellites and their shape cause numerous disputes among supporters of various theories of the origin of Phobos and Deimos. It is assumed that these are asteroids captured by the red planet at the dawn of the formation of the solar system. The supplier of material for the satellites of Mars is the asteroid belt, located between the fourth planet and Jupiter.
Proponents of another version of the origin of the satellites of the red planet are inclined to their artificial nature. The ancient Martian civilization could create and launch two artificially created celestial bodies.
When Earth and Mars are observed from some distance, it becomes apparent that they exhibit some striking differences. In the first case, the predominant colors are white and blue, corresponding to clouds and oceans, with brown shades of the continents. Thus, the existence of water in its various states (solid in polar glaciers, liquid in the oceans and seas, and in a gaseous state in the atmosphere) is obvious. And the presence of water implies the existence of life.
In fact, even from orbiting satellites, one can notice the intense biological activity of the planet. This can be seen from the Antarctic sea ice or the seasonal color changes of the woodlands.
Earth (the first full picture of the planet taken from Apollo 17, with Antarctica at the top) and Mars (image taken by HST). Please note that the images are not in real scale, since Mars is much smaller than our planet (equatorial diameters of 12,756.28 and 6,794.4 kilometers, respectively).
Red Planet
Mars is completely different. Its surface is dominated by various shades of orange, caused by a high content of iron oxide. Depending on the season and the position of the Red Planet relative to the Earth, one of the poles of Mars may be visible to astronomers, in which case dry ice (solid carbon dioxide) gives it a white color. However, several studies in recent years have made scientists understand what water is and that the dynamics of the life cycle of this compound on the planet are quite complex.
Mars has a thin atmosphere composed primarily of carbon dioxide (95.32%), nitrogen (2.7%), argon (1.4%), and traces of oxygen (0.13%). The atmosphere of the Earth, on the other hand, consists mainly of nitrogen (78.1%), oxygen (20.94%), argon (0.93%) and a variable amount of carbon dioxide (about 0.035% and growing rapidly). Average temperatures on the planets vary widely: -55 degrees Celsius (ºC) in the case of Mars, with lows around -133 ºC and highs around +27 ºC; and an average of around +15 ºC in the case of the Earth with lows of -89.4 ºC (noted in Antarctica, although -93.2 ºC was recently recorded in satellite measurements) and maxima of +58 ºC measured in El Aziz , Libya.
The average temperature of the Earth depends on the greenhouse effect caused by gases in the atmosphere, mainly carbon dioxide, water vapor, ozone (oxygen molecules with three oxygen atoms instead of the two that we breathe) and methane. Otherwise, the average temperature on Earth would be about 33 ºC cooler, around -18 ºC, and so water would be in a solid state over most of the planet.
Internal structure
In the case of Mars and Earth, their internal structure is divided into three well-differentiated regions: crust, mantle, and core. However, unlike the Earth, the core of Mars is solid and does not create its own magnetic field. At the same time, Mars has local magnetic fields, which are relic remnants of the global field that existed, perhaps, when Mars had a partially liquid core. The virtual absence on the Red Planet of plate tectonics as we know it on Earth, causing strong volcanic activity and orogeny (mountain building), means that the Martian soil is much older than the ocean floor and continents of the Earth. For example, the great plains of the southern hemisphere, the Hellas Plain, were formed by the impact of a large celestial body about 3900 million years ago. In the case of the Earth, evidence of an event of this age would have long since disappeared from its face.
A comparison of the altitude profiles of the two planets shows that they are very different: while most of the Earth's continental land mass is concentrated in the northern hemisphere, where there is also no polar continent, the northern hemisphere on Mars is dominated by the great northern lowland, located at the level of a thousand meters below the zero altitude of Mars. It is located at an altitude where the pressure of the atmosphere is 6.1 millibars and the triple point of water is located, at which matter coexists in solid, liquid and gaseous at the same time. In the case of water, the exact value is 273.16 K (0.01 °C) at a pressure of 6.1173 millibars. Therefore, below the reference point for the heights of Mars (for example, at the level of Hellas Planitia), liquid water could be found if the temperature there were high enough.
Unlike what it looks like on Mars, oceans and seas predominate in the southern hemisphere of the Earth, although several continental masses stand out in the topographic profile of our planet, which rise to significant heights above sea level (for example, the Antarctic Plateau). The situation on Mars is more uniform. The biggest difference between the planets is that a large amount of solid water is concentrated at the South Pole of the Earth. It covers an area of about 14 million square kilometers in summer, but including sea ice, it can increase to 30 million. The size reached by Martian Antarctica is much smaller - about 140,000 square kilometers, and its composition is very different from the earth. As mentioned earlier, it is dominated by dry ice.
It is curious that in our Antarctica we find some close similarities with Mars, namely the presence of low temperatures and low humidity. This refers to the McMurdo Valley system very close to the coast, which geologically may have equivalents on Mars.
Is there life on Mars?
Whether life exists on Mars or not, or whether there has ever been any biological activity, remains an open question. Some studies show that the Martian land is too salty for life to develop there. However, on our planet there are many examples of living beings that develop in clearly hostile conditions. They are known as .
McMurdo Valley in Antarctica, off the coast. This system is generally free of snow and unusually dry. Therefore, it may be similar to some Martian regions. Source: NASA, Terra satellite and ASTER instrument. Spacecraft on Mars
Several spacecraft have recently successfully landed on Mars. One of them was the Phoenix Mars Lander that reached the surface of the planet far to the north in 2008. His data showed scientists a plain covered in polygonal shapes reminiscent of those found in similar regions of the Earth. This is permafrost, which hardens and melts seasonally, indicating the presence of water on the planet. Phoenix had the right tools to drill into and analyze these structures, including studying their chemical composition. He was trying to determine if there were any organic compounds (though not necessarily biological ones) in the Arctic plains of Mars.
Comparison of the Arctic plains on Mars (above) in an image from the US Phoenix Mars Lander and Earth (Svalbard, Norway, Arctic). The Curiosity rover later landed near the Martian equator in 2012. It is still in operation and has carried out many experiments during its work, including rock drilling.
In any case, we must remember that at least on our planet there are living creatures (extremophiles) that can grow in really amazing conditions: from acidic environments to underwater volcanic calderas at high temperatures. A typical example of such a place is the Rio Tinto ecosystem. Unfortunately, it cannot be ruled out that some of the probes that have landed on the Red Planet may have contaminated it with biological material.
Both planets have interesting similarities and big differences.
Most of Mars is still to be discovered, and most likely not to us, but to future generations of earthlings.
Mars is the fourth largest planet from the Sun and the seventh (penultimate) largest planet in the solar system; the mass of the planet is 10.7% of the mass of the Earth. Named after Mars - the ancient Roman god of war, corresponding to the ancient Greek Ares. Mars is sometimes referred to as the "red planet" because of the reddish hue of the surface given to it by iron oxide.
Mars is a terrestrial planet with a rarefied atmosphere (the pressure at the surface is 160 times less than the earth's). The features of the surface relief of Mars can be considered impact craters like those of the moon, as well as volcanoes, valleys, deserts and polar ice caps like those of the earth.
Mars has two natural satellites - Phobos and Deimos (translated from ancient Greek - "fear" and "horror" - the names of the two sons of Ares who accompanied him in battle), which are relatively small (Phobos - 26x21 km, Deimos - 13 km across ) and have an irregular shape.
The great oppositions of Mars, 1830-2035
| Year | date | Distance a. e. |
|---|---|---|
| 1830 | September 19 | 0,388 |
| 1845 | August 18 | 0,373 |
| 1860 | July 17th | 0,393 |
| 1877 | September 5 | 0,377 |
| 1892 | August 4 | 0,378 |
| 1909 | September 24 | 0,392 |
| 1924 | August 23 | 0,373 |
| 1939 | July 23 | 0,390 |
| 1956 | 10 September | 0,379 |
| 1971 | 10th of August | 0,378 |
| 1988 | September 22nd | 0,394 |
| 2003 | August 28 | 0,373 |
| 2018 | July 27 | 0,386 |
| 2035 | September 15th | 0,382 |
Mars is the fourth farthest from the Sun (after Mercury, Venus and Earth) and the seventh largest (exceeds only Mercury in mass and diameter) planet of the solar system. The mass of Mars is 10.7% of the mass of the Earth (6.423 1023 kg versus 5.9736 1024 kg for the Earth), the volume is 0.15 of the volume of the Earth, and the average linear diameter is 0.53 of the diameter of the Earth (6800 km).
The relief of Mars has many unique features. The Martian extinct volcano Mount Olympus is the highest mountain in the solar system, and the Mariner Valley is the largest canyon. In addition, in June 2008, three papers published in the journal Nature provided evidence for the existence of the largest known impact crater in the solar system in the northern hemisphere of Mars. It is 10,600 km long and 8,500 km wide, about four times larger than the largest impact crater previously discovered on Mars, near its south pole.
In addition to similar surface topography, Mars has a rotation period and seasons similar to Earth's, but its climate is much colder and drier than Earth's.
Until the first flyby of Mars by the Mariner 4 spacecraft in 1965, many researchers believed that there was liquid water on its surface. This opinion was based on observations of periodic changes in light and dark areas, especially in polar latitudes, which were similar to continents and seas. Dark furrows on the surface of Mars have been interpreted by some observers as irrigation channels for liquid water. It was later proven that these furrows were an optical illusion.
Due to low pressure, water cannot exist in a liquid state on the surface of Mars, but it is likely that conditions were different in the past, and therefore the presence of primitive life on the planet cannot be ruled out. On July 31, 2008, water in the state of ice was discovered on Mars by NASA's Phoenix spacecraft.
In February 2009, the orbital research constellation in Mars' orbit had three functioning spacecraft: Mars Odyssey, Mars Express and Mars Reconnaissance Satellite, more than around any other planet besides Earth.
The surface of Mars is currently explored by two rovers: "Spirit" and "Opportunity". There are also several inactive landers and rovers on the surface of Mars that have completed research.
The geological data they collected suggests that most of the surface of Mars was previously covered with water. Observations over the past decade have made it possible to detect weak geyser activity in some places on the surface of Mars. According to observations from the Mars Global Surveyor spacecraft, some parts of the south polar cap of Mars are gradually receding.
Mars can be seen from Earth with the naked eye. Its apparent stellar magnitude reaches 2.91m (at the closest approach to the Earth), yielding in brightness only to Jupiter (and even then not always during the great confrontation) and Venus (but only in the morning or evening). As a rule, during a great opposition, orange Mars is the brightest object in the earth's night sky, but this happens only once every 15-17 years for one to two weeks.
Orbital characteristics
The minimum distance from Mars to the Earth is 55.76 million km (when the Earth is exactly between the Sun and Mars), the maximum is about 401 million km (when the Sun is exactly between the Earth and Mars).
The average distance from Mars to the Sun is 228 million km (1.52 AU), the period of revolution around the Sun is 687 Earth days. The orbit of Mars has a rather noticeable eccentricity (0.0934), so the distance to the Sun varies from 206.6 to 249.2 million km. The orbital inclination of Mars is 1.85°.
Mars is closest to Earth during opposition, when the planet is in the opposite direction from the Sun. Oppositions are repeated every 26 months at different points in the orbit of Mars and the Earth. But once every 15-17 years, the opposition occurs at a time when Mars is near its perihelion; in these so-called great oppositions (the last was in August 2003), the distance to the planet is minimal, and Mars reaches its largest angular size of 25.1" and brightness of 2.88m.
physical characteristics
Size comparison of Earth (average radius 6371 km) and Mars (average radius 3386.2 km)
In terms of linear size, Mars is almost half the size of the Earth - its equatorial radius is 3396.9 km (53.2% of the Earth's). The surface area of Mars is roughly equal to the land area of Earth.
The polar radius of Mars is about 20 km less than the equatorial one, although the period of rotation of the planet is longer than that of the Earth, which gives reason to assume a change in the rate of rotation of Mars with time.
The mass of the planet is 6.418 1023 kg (11% of the mass of the Earth). The free fall acceleration at the equator is 3.711 m/s (0.378 Earth); the first escape velocity is 3.6 km/s and the second is 5.027 km/s.
The planet's rotation period is 24 hours 37 minutes 22.7 seconds. Thus, a Martian year consists of 668.6 Martian solar days (called sols).
Mars rotates around its axis, which is inclined to the perpendicular plane of the orbit at an angle of 24°56?. The tilt of the axis of rotation of Mars causes the change of seasons. At the same time, the elongation of the orbit leads to large differences in their duration - for example, the northern spring and summer, taken together, last 371 sols, that is, noticeably more than half of the Martian year. At the same time, they fall on the part of Mars' orbit that is farthest from the Sun. Therefore, on Mars, northern summers are long and cool, while southern summers are short and hot.
Atmosphere and climate
Atmosphere of Mars, photo of the Viking orbiter, 1976. Halle's "smiley crater" is visible on the left
The temperature on the planet ranges from -153 at the pole in winter to over +20 °C at the equator at noon. The average temperature is -50°C.
The atmosphere of Mars, which consists mainly of carbon dioxide, is very rarefied. The pressure at the surface of Mars is 160 times less than the earth's - 6.1 mbar at the average surface level. Due to the large elevation difference on Mars, the pressure near the surface varies greatly. The approximate thickness of the atmosphere is 110 km.
According to NASA (2004), the atmosphere of Mars consists of 95.32% carbon dioxide; it also contains 2.7% nitrogen, 1.6% argon, 0.13% oxygen, 210 ppm water vapor, 0.08% carbon monoxide, nitric oxide (NO) - 100 ppm, neon (Ne) - 2, 5 ppm, semi-heavy water hydrogen-deuterium-oxygen (HDO) 0.85 ppm, krypton (Kr) 0.3 ppm, xenon (Xe) - 0.08 ppm.
According to the data of the AMS Viking descent vehicle (1976), about 1-2% argon, 2-3% nitrogen, and 95% carbon dioxide were determined in the Martian atmosphere. According to the data of AMS "Mars-2" and "Mars-3", the lower boundary of the ionosphere is at an altitude of 80 km, the maximum electron density of 1.7 105 electrons/cm3 is located at an altitude of 138 km, the other two maxima are at altitudes of 85 and 107 km.
Radio translucence of the atmosphere at radio waves of 8 and 32 cm by the AMS "Mars-4" on February 10, 1974 showed the presence of the nighttime ionosphere of Mars with the main ionization maximum at an altitude of 110 km and an electron density of 4.6 103 electrons / cm3, as well as secondary maxima at an altitude 65 and 185 km.
Atmosphere pressure
According to NASA data for 2004, the pressure of the atmosphere at the middle radius is 6.36 mb. The density at the surface is ~0.020 kg/m3, the total mass of the atmosphere is ~2.5 1016 kg.
The change in atmospheric pressure on Mars depending on the time of day, recorded by the Mars Pathfinder lander in 1997.
Unlike the Earth, the mass of the Martian atmosphere varies greatly during the year due to the melting and freezing of the polar caps containing carbon dioxide. During winter, 20-30 percent of the entire atmosphere is frozen on the polar cap, which consists of carbon dioxide. Seasonal pressure drops, according to various sources, are the following values:
According to NASA (2004): from 4.0 to 8.7 mbar at the average radius;
According to Encarta (2000): 6 to 10 mbar;
According to Zubrin and Wagner (1996): 7 to 10 mbar;
According to the Viking-1 lander: from 6.9 to 9 mbar;
According to the Mars Pathfinder lander: from 6.7 mbar.
The Hellas Impact Basin is the deepest place to find the highest atmospheric pressure on Mars
At the landing site of the AMC Mars-6 probe in the Eritrean Sea, a surface pressure of 6.1 millibars was recorded, which at that time was considered the average pressure on the planet, and from this level it was agreed to count the heights and depths on Mars. According to the data obtained by this device during the descent, the tropopause is located at an altitude of about 30 km, where the pressure is 5·10-7 g/cm3 (as on Earth at an altitude of 57 km).
The Hellas (Mars) region is so deep that atmospheric pressure reaches about 12.4 millibars, which is above the triple point of water (~6.1 mb) and below the boiling point. At a sufficiently high temperature, water could exist there in a liquid state; at this pressure, however, water boils and turns into steam already at +10 °C.
At the top of the highest 27 km volcano Olympus, the pressure can be between 0.5 and 1 mbar (Zurek 1992).
Before the landers landed on the surface of Mars, the pressure was measured by attenuating radio signals from the AMS Mariner-4, Mariner-6 and Mariner-7 when they entered the Martian disk - 6.5 ± 2.0 mb at the average surface level, which is 160 times less than the earthly; the same result was shown by the spectral observations of AMS Mars-3. At the same time, in areas located below the average level (for example, in the Martian Amazon), the pressure, according to these measurements, reaches 12 mb.
Since the 1930s Soviet astronomers tried to determine the pressure of the atmosphere using photographic photometry - by the distribution of brightness along the diameter of the disk in different ranges of light waves. For this purpose, the French scientists B. Lyo and O. Dollfus made observations of the polarization of the light scattered by the Martian atmosphere. A summary of optical observations was published by the American astronomer J. de Vaucouleurs in 1951, and they obtained a pressure of 85 mb, overestimated by almost 15 times due to interference from atmospheric dust.
Climate
A microscopic photo of a 1.3 cm hematite nodule taken by the Opportunity rover on March 2, 2004 shows the presence of liquid water in the past
The climate, like on Earth, is seasonal. In the cold season, even outside the polar caps, light frost can form on the surface. The Phoenix device recorded snowfall, but the snowflakes evaporated before reaching the surface.
According to NASA (2004), the average temperature is ~210 K (-63 °C). According to Viking landers, the daily temperature range is from 184 K to 242 K (from -89 to -31 °C) (Viking-1), and wind speed: 2-7 m/s (summer), 5-10 m /s (autumn), 17-30 m/s (dust storm).
According to the Mars-6 landing probe, the average temperature of the Mars troposphere is 228 K, in the troposphere the temperature decreases by an average of 2.5 degrees per kilometer, and the stratosphere above the tropopause (30 km) has an almost constant temperature of 144 K.
According to researchers from the Carl Sagan Center, the process of warming has been going on on Mars in recent decades. Other experts believe that it is too early to draw such conclusions.
There is evidence that in the past the atmosphere could have been denser, and the climate warm and humid, and liquid water existed on the surface of Mars and it rained. The proof of this hypothesis is the analysis of the ALH 84001 meteorite, which showed that about 4 billion years ago the temperature of Mars was 18 ± 4 °C.
dust whirlwinds
Dust swirls photographed by the Opportunity rover on May 15, 2005. The numbers in the lower left corner indicate the time in seconds since the first frame
Since the 1970s as part of the Viking program, as well as the Opportunity rover and other vehicles, numerous dust whirlwinds were recorded. These are air turbulences that occur near the surface of the planet and raise a large amount of sand and dust into the air. Vortices are often observed on Earth (in English-speaking countries they are called dust demons - dust devil), but on Mars they can reach much larger sizes: 10 times higher and 50 times wider than the earth. In March 2005, a vortex cleared the solar panels off the Spirit rover.
Surface
Two-thirds of the surface of Mars is occupied by light areas, called continents, about a third - by dark areas, called seas. The seas are concentrated mainly in the southern hemisphere of the planet, between 10 and 40 ° latitude. There are only two large seas in the northern hemisphere - the Acidalian and the Great Syrt.
The nature of the dark areas is still a matter of controversy. They persist despite the fact that dust storms rage on Mars. At one time, this served as an argument in favor of the assumption that the dark areas are covered with vegetation. Now it is believed that these are just areas from which, due to their relief, dust is easily blown out. Large-scale images show that in fact, the dark areas consist of groups of dark bands and spots associated with craters, hills and other obstacles in the path of the winds. Seasonal and long-term changes in their size and shape are apparently associated with a change in the ratio of surface areas covered with light and dark matter.
The hemispheres of Mars are quite different in the nature of the surface. In the southern hemisphere, the surface is 1-2 km above the mean level and is densely dotted with craters. This part of Mars resembles the lunar continents. In the north, most of the surface is below average, there are few craters, and the main part is occupied by relatively smooth plains, probably formed as a result of lava flooding and erosion. This difference between the hemispheres remains a matter of debate. The boundary between the hemispheres follows approximately a great circle inclined at 30° to the equator. The boundary is wide and irregular and forms a slope towards the north. Along it there are the most eroded areas of the Martian surface.
Two alternative hypotheses have been put forward to explain the asymmetry of the hemispheres. According to one of them, at an early geological stage, the lithospheric plates "came together" (perhaps by accident) into one hemisphere, like the Pangea continent on Earth, and then "frozen" in this position. Another hypothesis involves the collision of Mars with a space body the size of Pluto.
Topographic map of Mars, from Mars Global Surveyor, 1999
A large number of craters in the southern hemisphere suggests that the surface here is ancient - 3-4 billion years. There are several types of craters: large craters with a flat bottom, smaller and younger cup-shaped craters similar to the moon, craters surrounded by a rampart, and elevated craters. The latter two types are unique to Mars - rimmed craters formed where liquid ejecta flowed over the surface, and elevated craters formed where a crater ejecta blanket protected the surface from wind erosion. The largest feature of impact origin is the Hellas Plain (about 2100 km across).
In a region of chaotic landscape near the hemispheric boundary, the surface experienced large areas of fracture and compression, sometimes followed by erosion (due to landslides or catastrophic release of groundwater) and flooding with liquid lava. Chaotic landscapes are often found at the head of large channels cut by water. The most acceptable hypothesis for their joint formation is the sudden melting of subsurface ice.
Mariner Valleys on Mars
In the northern hemisphere, in addition to vast volcanic plains, there are two areas of large volcanoes - Tharsis and Elysium. Tharsis is a vast volcanic plain with a length of 2000 km, reaching a height of 10 km above the average level. There are three large shield volcanoes on it - Mount Arsia, Mount Pavlina and Mount Askriyskaya. On the edge of Tharsis is the highest mountain on Mars and in the solar system, Mount Olympus. Olympus reaches 27 km in height in relation to its base and 25 km in relation to the average level of the surface of Mars, and covers an area of 550 km in diameter, surrounded by cliffs, in places reaching 7 km in height. The volume of Mount Olympus is 10 times the volume of the largest volcano on Earth, Mauna Kea. Several smaller volcanoes are also located here. Elysium - a hill up to six kilometers above the average level, with three volcanoes - the dome of Hecate, Mount Elysius and the dome of Albor.
According to others (Faure and Mensing, 2007), the height of Olympus is 21,287 meters above zero and 18 kilometers above the surrounding area, and the diameter of the base is approximately 600 km. The base covers an area of 282,600 km2. The caldera (depression in the center of the volcano) is 70 km wide and 3 km deep.
The Tharsis Upland is also crossed by many tectonic faults, often very complex and extended. The largest of them - the Mariner valleys - stretches in the latitudinal direction for almost 4000 km (a quarter of the circumference of the planet), reaching a width of 600 and a depth of 7-10 km; this fault is comparable in size to the East African Rift on Earth. On its steep slopes, the largest landslides in the solar system occur. The Mariner Valleys are the largest known canyon in the solar system. The canyon, which was discovered by the Mariner 9 spacecraft in 1971, could cover the entire territory of the United States, from ocean to ocean.
A panorama of Victoria Crater taken by the Opportunity rover. It was filmed over three weeks, between October 16 and November 6, 2006.
Panorama of the surface of Mars in the Husband Hill region, taken by the Spirit rover November 23-28, 2005.
Ice and polar ice caps
North polar cap in summer, photo by Mars Global Surveyor. A long wide fault that cuts through the cap on the left - Northern Fault
The appearance of Mars varies greatly depending on the time of year. First of all, changes in the polar caps are striking. They grow and shrink, creating seasonal phenomena in the atmosphere and on the surface of Mars. The southern polar cap can reach a latitude of 50°, the northern one also 50°. The diameter of the permanent part of the northern polar cap is 1000 km. As the polar cap in one of the hemispheres recedes in spring, details of the planet's surface begin to darken.
The polar caps consist of two components: seasonal - carbon dioxide and secular - water ice. According to the Mars Express satellite, the thickness of the caps can range from 1 m to 3.7 km. The Mars Odyssey spacecraft has discovered active geysers on the south polar cap of Mars. As NASA experts believe, jets of carbon dioxide with spring warming break up to a great height, taking dust and sand with them.
Photographs of Mars showing a dust storm. June - September 2001
The spring melting of the polar caps leads to a sharp increase in atmospheric pressure and the movement of large masses of gas to the opposite hemisphere. The speed of the winds blowing at the same time is 10-40 m/s, sometimes up to 100 m/s. The wind raises a large amount of dust from the surface, which leads to dust storms. Strong dust storms almost completely hide the surface of the planet. Dust storms have a noticeable effect on the temperature distribution in the Martian atmosphere.
In 1784, astronomer W. Herschel drew attention to seasonal changes in the size of the polar caps, by analogy with the melting and freezing of ice in the earth's polar regions. In the 1860s the French astronomer E. Lie observed a wave of darkening around the melting spring polar cap, which was then interpreted by the hypothesis of melt water spreading and vegetation growth. Spectrometric measurements that were carried out at the beginning of the 20th century. at the Lovell Observatory in Flagstaff, W. Slifer, however, did not show the presence of a line of chlorophyll, the green pigment of terrestrial plants.
From photographs of Mariner-7, it was possible to determine that the polar caps are several meters thick, and the measured temperature of 115 K (-158 ° C) confirmed the possibility that it consists of frozen carbon dioxide - “dry ice”.
The hill, which was called the Mitchell Mountains, located near the south pole of Mars, looks like a white island when the polar cap melts, since glaciers melt later in the mountains, including on Earth.
Data from the Martian Reconnaissance Satellite made it possible to detect a significant layer of ice under the scree at the foot of the mountains. The glacier hundreds of meters thick covers an area of thousands of square kilometers, and its further study can provide information about the history of the Martian climate.
Channels of "rivers" and other features
On Mars, there are many geological formations that resemble water erosion, in particular, dried up river beds. According to one hypothesis, these channels could have formed as a result of short-term catastrophic events and are not proof of the long-term existence of the river system. However, recent evidence suggests that the rivers have flowed for geologically significant periods of time. In particular, inverted channels (that is, channels elevated above the surrounding area) have been found. On Earth, such formations are formed due to the long-term accumulation of dense bottom sediments, followed by drying and weathering of the surrounding rocks. In addition, there is evidence of channel shifting in the river delta as the surface gradually rises.
In the southwestern hemisphere, in the Eberswalde crater, a river delta with an area of about 115 km2 was discovered. The river that washed over the delta was more than 60 km long.
Data from NASA's Spirit and Opportunity rovers also testify to the presence of water in the past (minerals have been found that could only form as a result of prolonged exposure to water). The device "Phoenix" discovered deposits of ice directly in the ground.
In addition, dark stripes have been found on the slopes of hills, indicating the appearance of liquid salt water on the surface in our time. They appear shortly after the onset of the summer period and disappear by winter, “flow around” various obstacles, merge and diverge. "It's hard to imagine that such structures could form not from fluid flows, but from something else," said NASA employee Richard Zurek.
Several unusual deep wells have been found on the Tharsis volcanic upland. Judging by the image of the Martian Reconnaissance Satellite, taken in 2007, one of them has a diameter of 150 meters, and the illuminated part of the wall goes no less than 178 meters deep. A hypothesis about the volcanic origin of these formations has been put forward.
Priming
The elemental composition of the surface layer of the Martian soil, according to the data of the landers, is not the same in different places. The main component of the soil is silica (20-25%), containing an admixture of iron oxide hydrates (up to 15%), which give the soil a reddish color. There are significant impurities of sulfur compounds, calcium, aluminum, magnesium, sodium (a few percent for each).
According to data from NASA's Phoenix probe (landing on Mars on May 25, 2008), the pH ratio and some other parameters of Martian soils are close to Earth's, and plants could theoretically be grown on them. "In fact, we found that the soil on Mars meets the requirements, and also contains the necessary elements for the emergence and maintenance of life both in the past, in the present and in the future," said Sam Kunaves, lead research chemist of the project. Also, according to him, many people can find this alkaline type of soil in “their backyard”, and it is quite suitable for growing asparagus.
There is also a significant amount of water ice in the ground at the landing site of the apparatus. The Mars Odyssey orbiter also discovered that there are deposits of water ice under the surface of the red planet. Later, this assumption was confirmed by other devices, but the question of the presence of water on Mars was finally resolved in 2008, when the Phoenix probe, which landed near the planet's north pole, received water from the Martian soil.
Geology and internal structure
In the past, on Mars, as on Earth, there was a movement of lithospheric plates. This is confirmed by the features of the magnetic field of Mars, the locations of some volcanoes, for example, in the province of Tharsis, as well as the shape of the Mariner Valley. The current state of affairs, when volcanoes can exist for a much longer time than on Earth and reach gigantic sizes, suggests that now this movement is rather absent. This is supported by the fact that shield volcanoes grow as a result of repeated eruptions from the same vent over a long period of time. On Earth, due to the movement of lithospheric plates, volcanic points constantly changed their position, which limited the growth of shield volcanoes, and possibly did not allow them to reach heights, as on Mars. On the other hand, the difference in the maximum height of volcanoes can be explained by the fact that, due to the lower gravity on Mars, it is possible to build higher structures that would not collapse under their own weight.
Comparison of the structure of Mars and other terrestrial planets
Modern models of the internal structure of Mars suggest that Mars consists of a crust with an average thickness of 50 km (and a maximum thickness of up to 130 km), a silicate mantle 1800 km thick, and a core with a radius of 1480 km. The density in the center of the planet should reach 8.5 g/cm2. The core is partially liquid and consists mainly of iron with an admixture of 14-17% (by mass) of sulfur, and the content of light elements is twice as high as in the core of the Earth. According to modern estimates, the formation of the core coincided with the period of early volcanism and lasted about a billion years. The partial melting of mantle silicates took approximately the same time. Due to the lower gravity on Mars, the pressure range in the mantle of Mars is much smaller than on Earth, which means that it has fewer phase transitions. It is assumed that the phase transition of olivine to spinel modification begins at fairly large depths - 800 km (400 km on Earth). The nature of the relief and other features suggest the presence of an asthenosphere consisting of zones of partially molten matter. For some regions of Mars, a detailed geological map has been compiled.
According to observations from orbit and analysis of the collection of Martian meteorites, the surface of Mars consists mainly of basalt. There is some evidence to suggest that, on part of the Martian surface, the material is more quartz-bearing than normal basalt and may be similar to andesitic rocks on Earth. However, these same observations can be interpreted in favor of the presence of quartz glass. A significant part of the deeper layer consists of granular iron oxide dust.
Mars magnetic field
Mars has a weak magnetic field.
According to the readings of the magnetometers of the Mars-2 and Mars-3 stations, the magnetic field strength at the equator is about 60 gammas, at the pole 120 gammas, which is 500 times weaker than the earth's. According to AMS Mars-5, the magnetic field strength at the equator was 64 gamma, and the magnetic moment was 2.4 1022 oersted cm2.
The magnetic field of Mars is extremely unstable, at various points on the planet its strength can differ from 1.5 to 2 times, and the magnetic poles do not coincide with the physical ones. This suggests that the iron core of Mars is relatively immobile in relation to its crust, that is, the planetary dynamo mechanism responsible for the Earth's magnetic field does not work on Mars. Although Mars does not have a stable planetary magnetic field, observations have shown that parts of the planet's crust are magnetized and that there has been a reversal of the magnetic poles of these parts in the past. The magnetization of these parts turned out to be similar to strip magnetic anomalies in the oceans.
One theory, published in 1999 and re-examined in 2005 (using the unmanned Mars Global Surveyor), is that these bands show plate tectonics 4 billion years ago before the planet's dynamo ceased to function, causing a sharp weakening magnetic field. The reasons for this sharp decline are unclear. There is an assumption that the functioning of the dynamo 4 billion. years ago is explained by the presence of an asteroid that rotated at a distance of 50-75 thousand kilometers around Mars and caused instability in its core. The asteroid then dropped to its Roche limit and collapsed. However, this explanation itself contains ambiguities, and is disputed in the scientific community.
Geological history
Global mosaic of 102 Viking 1 orbiter images from February 22, 1980.
Perhaps, in the distant past, as a result of a collision with a large celestial body, the rotation of the core stopped, as well as the loss of the main volume of the atmosphere. It is believed that the loss of the magnetic field occurred about 4 billion years ago. Due to the weak magnetic field, the solar wind penetrates the atmosphere of Mars almost unhindered, and many of the photochemical reactions under the action of solar radiation that occur on Earth in the ionosphere and above can be observed on Mars almost at its very surface.
The geological history of Mars includes the following three epochs:
Noachian Epoch (named after "Noachian Land", a region of Mars): formation of the oldest extant surface of Mars. It continued in the period 4.5 billion - 3.5 billion years ago. During this epoch, the surface was scarred by numerous impact craters. The plateau of the province of Tharsis was probably formed during this period with intense water flow later.
Hesperian era: from 3.5 billion years ago to 2.9 - 3.3 billion years ago. This era is marked by the formation of huge lava fields.
Amazonian era (named after the "Amazonian plain" on Mars): 2.9-3.3 billion years ago to the present day. The regions formed during this epoch have very few meteorite craters, but otherwise they are completely different. Mount Olympus was formed during this period. At this time, lava flows were pouring in other parts of Mars.
Moons of Mars
The natural satellites of Mars are Phobos and Deimos. Both were discovered by the American astronomer Asaph Hall in 1877. Phobos and Deimos are irregularly shaped and very small. According to one hypothesis, they may represent asteroids like (5261) Eureka from the Trojan group of asteroids captured by the gravitational field of Mars. The satellites are named after the characters accompanying the god Ares (that is, Mars) - Phobos and Deimos, personifying fear and horror, who helped the god of war in battles.
Both satellites rotate around their axes with the same period as around Mars, therefore they are always turned to the planet by the same side. The tidal influence of Mars gradually slows down the movement of Phobos, and eventually will lead to the fall of the satellite to Mars (while maintaining the current trend), or to its disintegration. On the contrary, Deimos is moving away from Mars.
Both satellites have a shape approaching a triaxial ellipsoid, Phobos (26.6x22.2x18.6 km) is somewhat larger than Deimos (15x12.2x10.4 km). The surface of Deimos looks much smoother due to the fact that most of the craters are covered with fine-grained matter. Obviously, on Phobos, which is closer to the planet and more massive, the substance ejected during meteorite impacts either hit the surface again or fell on Mars, while on Deimos it remained in orbit around the satellite for a long time, gradually settling and hiding uneven terrain.
Life on Mars
The popular idea that Mars was inhabited by intelligent Martians became widespread in the late 19th century.
Schiaparelli's observations of the so-called canals, combined with Percival Lowell's book on the same subject, popularized the idea of a planet that was getting drier, colder, dying, and had an ancient civilization doing irrigation work.
Numerous other sightings and announcements by famous people gave rise to the so-called "Mars Fever" around this topic. In 1899, while studying atmospheric interference in a radio signal using receivers at the Colorado Observatory, inventor Nikola Tesla observed a repeating signal. He then speculated that it might be a radio signal from other planets such as Mars. In a 1901 interview, Tesla said that the idea came to him that interference could be caused artificially. Although he could not decipher their meaning, it was impossible for him that they arose completely by chance. In his opinion, it was a greeting from one planet to another.
Tesla's theory was strongly supported by the famous British physicist William Thomson (Lord Kelvin), who, visiting the United States in 1902, said that in his opinion Tesla had picked up the Martian signal sent to the United States. However, Kelvin then vehemently denied this statement before he left America: "In fact, I said that the inhabitants of Mars, if they exist, can certainly see New York, in particular the light from electricity."
Today, the presence of liquid water on its surface is considered a condition for the development and maintenance of life on the planet. There is also a requirement that the planet's orbit be in the so-called habitable zone, which for the solar system begins behind Venus and ends with the semi-major axis of the orbit of Mars. During perihelion, Mars is within this zone, but a thin atmosphere with low pressure prevents the appearance of liquid water over a large area for a long period. Recent evidence suggests that any water on the surface of Mars is too salty and acidic to support permanent terrestrial life.
The lack of a magnetosphere and the extremely thin atmosphere of Mars are also a problem for sustaining life. There is a very weak movement of heat flows on the surface of the planet, it is poorly isolated from bombardment by solar wind particles, in addition, when heated, water instantly evaporates, bypassing the liquid state due to low pressure. Mars is also on the threshold of the so-called. "geological death". The end of volcanic activity apparently stopped the circulation of minerals and chemical elements between the surface and the interior of the planet.
Evidence suggests that the planet was previously much more prone to life than it is now. However, to date, the remains of organisms have not been found on it. Under the Viking program, carried out in the mid-1970s, a series of experiments were conducted to detect microorganisms in the Martian soil. It has shown positive results, such as a temporary increase in CO2 release when soil particles are placed in water and nutrient media. However, then this evidence of life on Mars was disputed by some scientists [by whom?]. This led to their lengthy dispute with NASA scientist Gilbert Lewin, who claimed that the Viking had discovered life. After re-evaluating the Viking data in the light of current scientific knowledge about extremophiles, it was determined that the experiments carried out were not perfect enough to detect these life forms. Moreover, these tests could even kill the organisms, even if they were contained in the samples. Tests conducted by the Phoenix Program have shown that the soil has a very alkaline pH and contains magnesium, sodium, potassium and chloride. The nutrients in the soil are sufficient to support life, but life forms must be protected from intense ultraviolet light.
Interestingly, in some meteorites of Martian origin, formations were found that resemble the simplest bacteria in shape, although they are inferior to the smallest terrestrial organisms in size. One of these meteorites is ALH 84001, found in Antarctica in 1984.
According to the results of observations from the Earth and data from the Mars Express spacecraft, methane was detected in the atmosphere of Mars. Under the conditions of Mars, this gas decomposes rather quickly, so there must be a constant source of replenishment. Such a source can be either geological activity (but no active volcanoes have been found on Mars), or the vital activity of bacteria.
Astronomical observations from the surface of Mars
After the landings of automatic vehicles on the surface of Mars, it became possible to conduct astronomical observations directly from the surface of the planet. Due to the astronomical position of Mars in the solar system, the characteristics of the atmosphere, the period of revolution of Mars and its satellites, the picture of the night sky of Mars (and astronomical phenomena observed from the planet) differs from the earth's and in many ways seems unusual and interesting.
Sky color on Mars
During sunrise and sunset, the Martian sky at the zenith has a reddish-pink color, and in close proximity to the disk of the Sun - from blue to purple, which is completely opposite to the picture of earthly dawns.
At noon, the sky of Mars is yellow-orange. The reason for such differences from the color scheme of the earth's sky is the properties of the thin, rarefied atmosphere of Mars containing suspended dust. On Mars, Rayleigh scattering of rays (which on Earth is the cause of the blue color of the sky) plays an insignificant role, its effect is weak. Presumably, the yellow-orange coloration of the sky is also caused by the presence of 1% magnetite in dust particles constantly suspended in the Martian atmosphere and raised by seasonal dust storms. Twilight begins long before sunrise and lasts long after sunset. Sometimes the color of the Martian sky takes on a purple hue as a result of light scattering on microparticles of water ice in clouds (the latter is a rather rare phenomenon).
sun and planets
The angular size of the Sun, observed from Mars, is less than that visible from the Earth and is 2/3 of the latter. Mercury from Mars will be practically inaccessible to observation with the naked eye due to its extreme proximity to the Sun. The brightest planet in the sky of Mars is Venus, in second place is Jupiter (its four largest satellites can be observed without a telescope), in third is Earth.
Earth is an inner planet to Mars, just like Venus is to Earth. Accordingly, from Mars, the Earth is observed as a morning or evening star, rising before dawn or visible in the evening sky after sunset.
The maximum elongation of the Earth in the sky of Mars will be 38 degrees. To the naked eye, the Earth will be visible as a bright (maximum visible magnitude of about -2.5) greenish star, next to which the yellowish and dimmer (about 0.9) star of the Moon will be easily distinguishable. In a telescope, both objects will show the same phases. The revolution of the Moon around the Earth will be observed from Mars as follows: at the maximum angular distance of the Moon from the Earth, the naked eye will easily separate the Moon and the Earth: in a week the “stars” of the Moon and the Earth will merge into a single star inseparable by the eye, in another week the Moon will again be visible at maximum distance, but on the other side of the Earth. Periodically, an observer on Mars will be able to see the passage (transit) of the Moon across the Earth's disk or, conversely, the covering of the Moon by the Earth's disk. The maximum apparent distance of the Moon from the Earth (and their apparent brightness) when viewed from Mars will vary significantly depending on the relative position of the Earth and Mars, and, accordingly, the distance between the planets. During the epoch of oppositions, it will be about 17 minutes of arc, at the maximum distance of Earth and Mars - 3.5 minutes of arc. Earth, like other planets, will be observed in the constellation band of the Zodiac. An astronomer on Mars will also be able to observe the passage of the Earth across the disk of the Sun, the next one will occur on November 10, 2084.
Moons - Phobos and Deimos
Passage of Phobos across the disk of the Sun. Pictures of Opportunity
Phobos, when observed from the surface of Mars, has an apparent diameter of about 1/3 of the disk of the Moon in the earth's sky and an apparent magnitude of about -9 (approximately like the Moon in the phase of the first quarter). Phobos rises in the west and sets in the east, only to rise again 11 hours later, thus crossing the sky of Mars twice a day. The movement of this fast moon across the sky will be easily seen during the night, as will the changing phases. The naked eye can distinguish the largest feature of the relief of Phobos - the crater Stickney. Deimos rises in the east and sets in the west, looks like a bright star without a noticeable visible disk, about magnitude -5 (slightly brighter than Venus in the earth's sky), slowly crossing the sky for 2.7 Martian days. Both satellites can be observed in the night sky at the same time, in which case Phobos will move towards Deimos.
The brightness of both Phobos and Deimos is sufficient for objects on the surface of Mars to cast sharp shadows at night. Both satellites have a relatively small inclination of the orbit to the equator of Mars, which excludes their observation in the high northern and southern latitudes of the planet: for example, Phobos never rises above the horizon north of 70.4 ° N. sh. or south of 70.4°S sh.; for Deimos these values are 82.7°N. sh. and 82.7°S sh. On Mars, an eclipse of Phobos and Deimos can be observed when they enter the shadow of Mars, as well as an eclipse of the Sun, which is only annular due to the small angular size of Phobos compared to the solar disk.
Celestial sphere
The north pole on Mars, due to the inclination of the planet's axis, is in the constellation Cygnus (equatorial coordinates: right ascension 21h 10m 42s, declination +52 ° 53.0? and is not marked by a bright star: the closest star to the pole is a dim star of the sixth magnitude BD +52 2880 (other its designations are HR 8106, HD 201834, SAO 33185. The south celestial pole (coordinates 9h 10m 42s and -52° 53.0) is a couple of degrees from the star Kappa Parusov (apparent magnitude 2.5) - it, in principle , can be considered the South Pole Star of Mars.
The zodiac constellations of the Martian ecliptic are similar to those observed from the Earth, with one difference: when observing the annual movement of the Sun among the constellations, it (like other planets, including the Earth), leaving the eastern part of the constellation Pisces, will pass for 6 days through the northern part of the constellation Cetus before how to re-enter the western part of Pisces.
History of the study of Mars
The exploration of Mars began a long time ago, even 3.5 thousand years ago, in ancient Egypt. The first detailed accounts of the position of Mars were made by Babylonian astronomers, who developed a number of mathematical methods to predict the position of the planet. Using the data of the Egyptians and Babylonians, ancient Greek (Hellenistic) philosophers and astronomers developed a detailed geocentric model to explain the movement of the planets. A few centuries later, Indian and Islamic astronomers estimated the size of Mars and its distance from Earth. In the 16th century, Nicolaus Copernicus proposed a heliocentric model to describe the solar system with circular planetary orbits. His results were revised by Johannes Kepler, who introduced a more accurate elliptical orbit for Mars, coinciding with the observed one.
In 1659, Francesco Fontana, looking at Mars through a telescope, made the first drawing of the planet. He depicted a black spot in the center of a clearly defined sphere.
In 1660, two polar caps were added to the black spot, added by Jean Dominique Cassini.
In 1888, Giovanni Schiaparelli, who studied in Russia, gave the first names to individual surface details: the seas of Aphrodite, Eritrean, Adriatic, Cimmerian; lakes of the Sun, Lunar and Phoenix.
The heyday of telescopic observations of Mars came at the end of the 19th - the middle of the 20th century. It is largely due to public interest and well-known scientific disputes around the observed Martian channels. Among the astronomers of the pre-space era who made telescopic observations of Mars during this period, the most famous are Schiaparelli, Percival Lovell, Slifer, Antoniadi, Barnard, Jarry-Deloge, L. Eddy, Tikhov, Vaucouleurs. It was they who laid the foundations of areography and compiled the first detailed maps of the surface of Mars - although they turned out to be almost completely incorrect after flights of automatic probes to Mars.
Mars colonization
Estimated view of Mars after terraforming
Relatively close to terrestrial natural conditions make this task somewhat easier. In particular, there are places on Earth where natural conditions are similar to those on Mars. Extremely low temperatures in the Arctic and Antarctica are comparable to even the lowest temperatures on Mars, and the equator of Mars during the summer months is as warm (+20 °C) as on Earth. Also on Earth there are deserts similar in appearance to the Martian landscape.
But there are significant differences between Earth and Mars. In particular, the magnetic field of Mars is weaker than the earth's by about 800 times. Together with a rarefied (hundreds of times in comparison with the Earth) atmosphere, this increases the amount of ionizing radiation reaching its surface. Measurements carried out by the American unmanned vehicle The Mars Odyssey showed that the radiation background in the orbit of Mars is 2.2 times higher than the radiation background at the International Space Station. The average dose was approximately 220 millirads per day (2.2 milligrays per day or 0.8 grays per year). The amount of radiation received as a result of staying in such a background for three years is approaching the established safety limits for astronauts. On the surface of Mars, the radiation background is somewhat lower and the dose is 0.2-0.3 Gy per year, varying significantly depending on the terrain, altitude and local magnetic fields.
The chemical composition of the minerals common on Mars is more diverse than that of other celestial bodies near the Earth. According to the 4Frontiers corporation, they are enough to supply not only Mars itself, but also the Moon, the Earth and the asteroid belt.
The flight time from Earth to Mars (with current technologies) is 259 days in a semi-ellipse and 70 days in a parabola. To communicate with potential colonies, radio communication can be used, which has a delay of 3-4 minutes in each direction during the closest approach of the planets (which repeats every 780 days) and about 20 minutes. at the maximum distance of the planets; see Configuration (astronomy).
To date, no practical steps have been taken for the colonization of Mars, but colonization is being developed, for example, the Centenary Spacecraft project, the development of a habitation module for staying on the Deep Space Habitat planet.
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 deep purple, and bright stars are visible even during the day in calm, still 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. Mars has climate zones similar to those on Earth. In the equatorial belt at noon the temperature rises to +20-25 °C, and at night it drops to -40 °C. 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 decreased, permafrost and polar caps appeared, which are still observed today.
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).
> Comparison of Mars and Earth
Comparing Mars and Earth. How they differ and are similar: dimensions, atmosphere, gravity, distance to the Sun, living conditions, characteristics in numbers with a photo.
Previously, scientists thought that the Martian surface was littered with a system of channels. Because of this, they began to believe that the planet looks like ours and is capable of having life. But as we studied in detail, we realized that there are many differences between the objects.
Now the Red Planet is a frosty desert, but once this world was similar to ours. They converge in size, axial tilt, structure, composition, and presence of water. But differences prevent us from quickly colonizing the planet. Let's see how Mars and planet Earth differ.
Comparison of size, mass, orbit of Earth and Mars
The average earth radius is 6371 km, and the mass is 5.97 × 10 24 kg, which is why we are in 5th place in terms of size and massiveness. The radius of Mars is 3396 km at its equator (0.53 of the earth), and the mass is 6.4185 x 10 23 kg (15% of the earth). In the top photo, you can see how much smaller Mars is than Earth.
The terrestrial volume is 1.08321 x 10 12 km 3, and the Martian volume is 1.6318 × 10¹¹ km³ (0.151 Earth). The surface density of Mars is 3.711 m / s², which is 37.6% of the Earth.
Their orbital paths are completely different. The average distance of the Earth from the Sun is 149,598,261 km, and fluctuations are from 147,095,000 km to 151,930,000 km. The maximum distance of Mars is 249,200,000,000 km, and the proximity is 206,700,000,000 km. At the same time, its orbital period reaches 686.971 days.
But their sidereal turnover is almost the same. If we have 23 hours, 56 minutes and 4 seconds, then Mars has 24 hours and 40 minutes. The photo shows the level of tilt of the axis of Mars and the Earth.
There is also a similarity in axial tilt: Martian 25.19° versus Earth's 23°. This means that seasonality can be expected from the Red Planet.
Structure and composition of Earth and Mars
Earth and Mars are representatives of the terrestrial planets, which means they have a similar structure. It is a metallic core with a mantle and crust. But the Earth's density (5.514 g/cm 3 ) is higher than the Martian one (3.93 g/cm 3 ), that is, Mars contains lighter elements. The bottom figure compares the structure of Mars and the planet Earth.
The Martian core extends for 1795 +/-65 km and is represented by iron and nickel, as well as 16-17% sulfur. Both planets have a silicate mantle around the core and a hard surface crust. The earth's mantle extends for 2890 km and consists of silicate rocks with iron and magnesium, and the crust covers 40 km, where in addition to iron and magnesium there is granite.
The Martian mantle is only 1300-1800 km and is also represented by silicate rock. But it is somewhat viscous. Kora - 50-125 km. It turns out that with almost the same structure, they differ in the thickness of the layers.
Surface features of Earth and Mars
It is here that the greatest contrast is noted. No wonder we are called the blue planet, which is overflowing with water. But the Red Planet is a cold and deserted place. There is a lot of dirt and iron oxide, which caused the red color. Water is present in the form of ice in the polar regions. Also, a small amount remains below the surface.
There are similarities in the landscape. Volcanoes, mountains, ridges, gorges, plateaus, canyons and plains are found on both planets. Mars also boasts the largest mountain in the solar system, Olympus Olympus, and a deep abyss, the Mariner Valley.
Both planets suffered from asteroid and meteor attacks. But on Mars, these footprints are better preserved, and some are billions of years old. It's all about air pressure and the absence of precipitation, which destroy formations on our planet.
Attention is drawn to the Martian channels and ravines, through which water could flow in the past. It is believed that the cause of creation could be water erosion. They extend 2000 km long and 100 km wide.
Atmosphere and temperature of Earth and Mars
Here the planets are radically different. The Earth has a dense atmospheric layer, divided into 5 balls. Mars has a thin atmosphere and a pressure of 0.4-0.87 kPa. The Earth's atmosphere is represented by nitrogen (78%) and oxygen (21%), while Mars' atmospheric composition is carbon dioxide (96%), argon (1.93%) and nitrogen (1.89%).
This also affected the difference in temperature indicators. The Earth's average is 14°C, the maximum is 70.7°C, and the minimum drops to -89.2°C.
Due to the thinness of the atmosphere and distance from the Sun, Mars is much cooler. The average falls to -46°C, the minimum reaches -143°C, and can warm up to 35°C. The Martian atmosphere also contains a huge amount of dust (particle size - 1.5 micrometers), which makes the planet appear red.
Magnetic fields of Earth and Mars
The earth's dynamo is provided by the rotation of the core, which generates currents and a magnetic field. This process is extremely important, because it protects earthly life. See the magnetic fields of Mars and Earth in a NASA diagram.
The Earth's magnetosphere functions as a shield that prevents dangerous cosmic rays from reaching the surface. But in Mars it is weak and devoid of integrity. It is believed that these are only remnants of the original magnetosphere, which is now dispersed in various parts of the planet. The greatest tension is closer to the south side.
Perhaps the magnetosphere has disappeared due to an intense meteor attack. Or it's all about the cooling process, which led to the stop of the dynamo 4.2 billion years ago. Then the solar wind set to work, which carried the remains along with the atmosphere and water.
Satellites of Earth and Mars
The planets have satellites. Our Moon is the only neighbor responsible for the tides. It has been with us for a long time and imprinted in many cultures. This is not just one of the largest satellites in the system, but the most studied.
Two moons orbit Mars: Phobos and Deimos. They were found in 1877. Their names are given in honor of the sons of the god of war Ares: fear and horror. Phobos extends for 22 km, and its remoteness borders between 9234.42 km and 9517.58 km. One pass takes 7 hours. It is believed that in 10-50 million years the satellite will crash into the planet.
The diameter of Deimos is 12 km, and the orbital path is 23455.5 km - 23470.9 km. The bypass takes 1.26 days. There are also additional satellites, whose diameter does not exceed 100 m. They can form a dust ring.
It is believed that earlier Phobos and Deimos were asteroids attracted by gravity. This is hinted at by their composition and low albedo.
Conclusion about Earth and Mars
We considered two planets. Let's compare their main parameters (Earth is on the left, and Mars is on the right):
- Average radius: 6,371 km / 3,396 km.
- Weight: 59.7 x 10 23 kg / 6.42 x 10 23 kg.
- Volume: 10.8 x 10 11 km3 / 1.63 × 10¹¹ km³.
- Half axis: 0.983 - 1.015 a.u. / 1.3814 - 1.666 a.u.
- Pressure: 101.325 kPa / 0.4 - 0.87 kPa.
- Gravity: 9.8 m/s² / 3.711 m/s²
- Average temperature: 14°C / -46°C.
- Temperature fluctuation: ±160°C / ±178°C.
- Axial tilt: 23° / 25.19°.
- Day length: 24 hours / 24 hours and 40 minutes.
- Year length: 365.25 days / 686.971 days.
- Water: copious/intermittent (as ice).
- Polar ice caps: Yes / Yes.
We see that Mars, compared to us, is a small and deserted planet. Its characteristics show that the colonialists will have to face a huge number of difficulties. And yet we are ready to take the risk and go on a journey. Moreover, the distance from Earth to Mars is relatively small. Perhaps one day we will make it our second home.
