The atmosphere of Mars - the chemical composition, weather conditions and climate in the past. Atmosphere of Mars Primary element of the atmosphere of Mars

Like any large planet, Mars has an atmosphere. It consists of a gaseous substance that the planet holds due to gravity. However, the air on Mars is very different from the earth.

General information about the atmosphere of Mars

The atmosphere of Mars is much thinner than that of Earth. Its height is 11 km, which is approximately 9-10% of the earth. This is caused by the planet's weak gravitational pull, unable to hold onto a wider layer of gas. The small thickness and density of the atmosphere causes such air phenomena that cannot be found on Earth.

Chemically, the atmosphere consists mainly of carbon dioxide.

The density of the atmosphere is also very low: more than 61 times less than the average density on Earth.

Due to its properties, the atmosphere is constantly exposed to the solar wind, losing matter and dispersing faster than on other planets. This process is called dissipation. This is because the planet Mars does not have a magnetic field.

Atmospheric structure

Even being thin, the Martian atmosphere is heterogeneous and has a layered structure. Its structure looks like this:

● Below all layers is the troposphere. It occupies the entire space from the surface to 20-30 km. The temperature here decreases evenly as it rises. The upper limit of the troposphere is not fixed, and changes its position throughout the year.

● Above is the stratomesosphere. The temperature in this part is approximately the same and equal to -133 ° C. It continues up to a height of 100 km above the surface, where the entire lower atmosphere ends with it.

● Everything above (up to the border where space begins) is called the upper atmosphere. Another name for this layer is the thermosphere, and its average temperature is from 200 to 350 K.

● Within it stands out the ionosphere, which, as the name implies, is characterized by a high level of ionization arising from solar radiation. It begins approximately in the same place as the entire upper part and has a length of approximately 400 km.

● At an altitude of about 230 km, the thermosphere ends. Its last layer is called ecobase.

● Not belonging to either the lower or the upper atmosphere define the chemosphere in which chemical reactions take place initiated by light. Due to the absence of any analogue of the Earth's Ozone layer on Mars, this layer begins at the surface level. And it ends at an altitude of 120 km.

So, the surface of Mars is covered with a rather thin and rarefied atmosphere, which, however, has a relatively complex structure. In total, the atmosphere of Mars consists of seven layers, but this number may vary in different sources, since scientists have not yet agreed on the nature of some layers.

Do not think that the layered structure indicates static. The atmosphere of Mars is also prone to change, like the earth's: it has both general circulation and partial movements of air currents.

Composition of the atmosphere

The chemical composition of the atmosphere of Mars is very different from that of Earth. The air on Mars is made up of the following gases:

● The basis of the atmosphere of the planet Mars is carbon dioxide. It occupies about 95% of its volume. It is the only heavy gas the planet can hold.

● The majority of carbon dioxide is CO2, but carbon monoxide CO also makes up a portion of it. This proportion is unusually small and leads scientists to theorize why CO is not accumulating.

● Nitrogen N2. It makes up a very small part of the atmosphere - only 2.7%. However, it can linger in the atmosphere only in the form of a double molecule. Radiation from the Sun constantly splits atmospheric nitrogen into atoms, after which it dissipates.

● Argon occupies 1.6% and is represented mainly by the heavy isotope argon-40.

● There is also oxygen on Mars, but it is contained mainly in the upper atmosphere and appears during the decomposition of other substances, from where it then passes to the lower layers. Because of this, at an altitude of about 110 km and above, there is 3-4 times more O2 than below this level. They cannot breathe.

● Ozone is the most uncertain gas in the Martian atmosphere. Its content depends on the air temperature, and therefore on the time of year, latitude and hemisphere.

● Methane on Mars, despite its low content in the atmosphere, is one of the most mysterious gases on the planet. It can have several sources, but two of the most relevant are: the influence of temperatures (for example, in volcanoes) and the processing of substances by bacteria and ruminants, after which bacterial methane is formed. The latter is of particular interest to astrobiology - it is what they are looking for on potentially inhabited planets to prove that they have life. What methane that appears on Mars in bursts can indicate is unknown.

● Organic compounds such as H2CO, HCl and SO2 are also found in the Martian atmosphere. They can clarify the issue discussed above, since their presence indicates the absence of volcanic activity - and therefore thermogenic methane.

● Water. Although its content is several hundred times less than in the driest regions of the Earth, it is still present.

● It is also worth mentioning that the atmosphere of Mars is filled with the smallest dust particles (mainly iron oxide). They make the atmosphere reddish-orange from the outside, and they are also responsible for the colors of the sky, the opposite of Earth: the daytime skies on Mars are yellow-brown, at sunset and dawn they turn pink, and around the Sun they are blue.

Clouds

The atmosphere of the Red Planet is capable of forming the same phenomena as the earth's. For example, there are clouds on Mars.

Vaporous water in the atmosphere of the planet Mars is extremely small, but still enough for the formation of clouds. Most often they are located at a height of one to three tens of kilometers above the surface. Concentrated water vapor collects into clouds mainly at the equator - where they can be observed all year round.

In addition, the cloud on Mars can also form CO2. Usually it is located above water (at an altitude of about 20 km).

There are also fogs on Mars. Most often - in lowlands and craters, at night.

Once upon a time, vortex-like systems of clouds were discovered in a picture of the Martian atmosphere. This was evidence of a more complex climatic phenomenon - a cyclone. On Earth, this is a common occurrence, but on other planets it is quite unusual. Nothing more is known about Martian cyclones yet.

There is no ordinary rain on Mars, but among natural phenomena, virga is sometimes observed - drops or snow that evaporate in the air before reaching the earth.

Greenhouse effect

The greenhouse effect on Mars is always discussed in the context of the discussion of liquid water that once existed on it. “Rivers” on the surface are already talking about this, but this was not enough for scientists, and they decided to find what allowed liquid H2O to appear.
When Mars was a young planet, its volcanoes were extremely active. Each volcanic explosion on Mars released carbon dioxide and methane, which decomposed under the action of sunlight, producing hydrogen and creating a “hydrogen greenhouse effect”. At some point, the concentration of the latter gas increased so much that it allowed the existence of lakes, rivers and even entire oceans of water. However, over time, the planet's atmosphere became thinner and could no longer provide conditions in which water would remain liquid. Right now, only water vapor or ice can be found on Mars. The transition from one state of aggregation to another occurs with the help of sublimation, bypassing the liquid stage. This can be called a unique feature in the history of the atmosphere of Mars, since this has not yet happened on any other planet. However, this is only a scientific theory.

Pressure

The average atmospheric pressure on Mars is 4.5 mmHg or 600 Pascals. This is one 169th of the average pressure on Earth. Such pressure makes it impossible for a person to survive on the surface without a spacesuit. People stranded on the open surface of the planet Mars without protection face instant death. The reason for this is the existence of the so-called Armstrong limit - the pressure level at which water boils at normal human body temperature. The pressure of the atmosphere on the surface of Mars is well below this limit.

dust devils

Dust storms that regularly occur on Mars are a feature of this planet. Their cause is storms on Mars, in which wind speeds reach 100 km / h. Air collects dust hanging in the atmosphere to a height of up to 50 km. This gives rise to those same dust storms on Mars. Most often they occur in the polar regions and rage for 1.5 - 3 months. Similarly, sandstorms occur on Mars. The only difference is that this time larger particles rise into the air, which have settled on the surface - sand.

However, if there is wind on Mars, then there must be dangerous air phenomena that it causes. For example, tornadoes. They, like storms, raise sand and dust into the air, but extend hundreds of meters wide and kilometers high and seem much more dangerous (even though their speed is three times lower than that of storms - only 30 km /h). Due to the same low density of the atmosphere, tornadoes on Mars look more like tornadoes. Their second name is dust devils. From orbit you can see how they leave black swirling tracks on a light sandy surface.

Radiation

Radiation on Mars is no less dangerous for people than dust or low pressure. There are two reasons for this: the weakness and rarefaction of the atmosphere and the absence of a magnetosphere near the planet Mars. The air part is not able to protect its surface from cosmic radiation. That is why in a few days spent on the planet without protection, the astronaut will receive an annual dose of radiation.

Terraforming

Despite all this, people still dream of subjugating Mars and even making it habitable. The atmosphere of Mars is one of the main obstacles on this path. However, it is proposed to terraform Mars not only by providing it with oxygen and a dense atmosphere, but also by creating a large source of space fuel. It is proposed to chemically decompose carbon dioxide into oxygen and CO, which can be used to provide a colony and fuel transport in order to establish a connection with the Earth.

Encyclopedic YouTube

1 / 5

✪ Project DISCOVER-AQ - Atmospheric Research (NASA in Russian)

✪ NASA in Russian: 01/18/13 - NASA video digest for the week

✪ NEGATIVE MASS [Science and Technology News]

✪ Mars, 1968, science fiction film essay, director Pavel Klushantsev

✪ 5 Signs of Life On Mars - The Countdown #37

Subtitles

Studying

The atmosphere of Mars was discovered even before the flights of automatic interplanetary stations to the planet. Thanks to spectral analysis and the oppositions of Mars with the Earth, which happen once every 3 years, astronomers already in the 19th century knew that it has a very homogeneous composition, more than 95% of which is carbon dioxide. When compared with 0.04% carbon dioxide in the Earth's atmosphere, it turns out that the mass of Martian atmospheric carbon dioxide exceeds the mass of Earth by almost 12 times, so that when Mars is terraformed, the carbon dioxide contribution to the greenhouse effect can create a climate comfortable for humans a little earlier than it is reached. pressure of 1 atmosphere, even taking into account the greater distance of Mars from the Sun.

Back in the early 1920s, the first measurements of the temperature of Mars were made using a thermometer placed at the focus of a reflecting telescope. Measurements by V. Lampland in 1922 gave an average surface temperature of Mars of 245 (−28 °C), E. Pettit and S. Nicholson in 1924 obtained 260 K (−13 °C). A lower value was obtained in 1960 by W. Sinton and J. Strong: 230 K (−43 ° C). The first estimates of pressure - averaged - were obtained only in the 60s using ground-based IR spectroscopes: a pressure of 25 ± 15 hPa obtained from the Lorentz broadening of carbon dioxide lines meant that it was the main component of the atmosphere.

The wind speed can be determined from the Doppler shift of the spectral lines. So, for this, the line shift was measured in the millimeter and submillimeter range, and measurements on the interferometer make it possible to obtain the distribution of velocities in the whole layer of great thickness.

The most detailed and accurate data on air and surface temperature, pressure, relative humidity and wind speed are continuously measured by the Rover Environmental Monitoring Station (REMS) instrument suite aboard the Curiosity rover, which has been operating in the Gale crater since 2012. And the MAVEN spacecraft, which has been orbiting Mars since 2014, is specifically designed to study the upper atmosphere in detail, their interaction with solar wind particles, and in particular the scattering dynamics.

A number of processes that are difficult or not yet possible for direct observation are subject only to theoretical modeling, but it is also an important research method.

Atmospheric structure

In general, the atmosphere of Mars is divided into lower and upper; the latter is considered to be the region above 80 km above the surface, where the processes of ionization and dissociation play an active role. A section is devoted to its study, which is commonly called aeronomy. Usually, when people talk about the atmosphere of Mars, they mean the lower atmosphere.

Also, some researchers distinguish two large shells - the homosphere and the heterosphere. In the homosphere, the chemical composition does not depend on height, since the processes of heat and moisture transfer in the atmosphere and their vertical exchange are entirely determined by turbulent mixing. Since molecular diffusion in the atmosphere is inversely proportional to its density, then from a certain level this process becomes predominant and is the main feature of the upper shell - the heterosphere, where molecular diffuse separation occurs. The interface between these shells, which is located at altitudes from 120 to 140 km, is called the turbopause.

lower atmosphere

From the surface to a height of 20-30 km stretches troposphere where the temperature decreases with height. The upper limit of the troposphere fluctuates depending on the time of year (the temperature gradient in the tropopause varies from 1 to 3 deg/km with an average value of 2.5 deg/km).

Above the tropopause is an isothermal region of the atmosphere - stratomesosphere stretching up to a height of 100 km. The average temperature of the stratomesosphere is exceptionally low and amounts to -133°C. Unlike the Earth, where the stratosphere contains predominantly all atmospheric ozone, on Mars its concentration is negligible (it is distributed from altitudes of 50 - 60 km to the very surface, where it is maximum).

upper atmosphere

Above the stratomesosphere extends the upper layer of the atmosphere - thermosphere. It is characterized by an increase in temperature with height up to a maximum value (200-350 K), after which it remains constant up to the upper limit (200 km). The presence of atomic oxygen was registered in this layer; its density at a height of 200 km reaches 5-6⋅10 7 cm −3 . The presence of a layer dominated by atomic oxygen (as well as the fact that the main neutral component is carbon dioxide) combines the atmosphere of Mars with the atmosphere of Venus.

Ionosphere- a region with a high degree of ionization - is located in the altitude range from about 80-100 to about 500-600 km. The content of ions is minimal at night and maximal during the day, when the main layer is formed at an altitude of 120-140 km due to the photoionization of carbon dioxide extreme ultraviolet solar radiation CO 2 + hν → CO 2 + + e -, as well as reactions between ions and neutral substances CO 2 + + O → O 2 + + CO and O + + CO 2 → O 2 + + CO. The concentration of ions, of which 90% O 2 + and 10% CO 2 +, reaches 10 5 per cubic centimeter (in other areas of the ionosphere it is 1-2 orders of magnitude lower). It is noteworthy that O 2 + ions predominate in the almost complete absence of molecular oxygen proper in the Martian atmosphere. The secondary layer is formed in the region of 110-115 km due to soft X-rays and knocked out fast electrons. At an altitude of 80-100 km, some researchers distinguish a third layer, sometimes manifested under the influence of cosmic dust particles that bring metal ions Fe + , Mg + , Na + into the atmosphere. However, later it was not only confirmed the appearance of the latter (moreover, over almost the entire volume of the upper atmosphere) due to the ablation of the substance of meteorites and other cosmic bodies entering the atmosphere of Mars, but also their constant presence in general. At the same time, due to the absence of a magnetic field on Mars, their distribution and behavior differ significantly from what is observed in the earth's atmosphere. Above the main maximum, other additional layers can also appear due to interaction with the solar wind. Thus, the layer of O+ ions is most pronounced at an altitude of 225 km. In addition to the three main types of ions (O 2 +, CO 2 and O +), relatively recently H 2 + , H 3 + , He + , C + , CH + , N + , NH + , OH + , H 2 O + , H 3 O + , N 2 + /CO + , HCO + /HOC + /N 2 H + , NO + , HNO + , HO 2 + , Ar + , ArH + , Ne + , CO 2 ++ and HCO2+. Above 400 km, some authors distinguish an "ionopause", but there is no consensus on this yet.

As for the plasma temperature, the ion temperature near the main maximum is 150 K, increasing to 210 K at an altitude of 175 km. Higher, the thermodynamic equilibrium of ions with a neutral gas is significantly disturbed, and their temperature rises sharply to 1000 K at an altitude of 250 km. The temperature of electrons can be several thousand kelvins, apparently due to the magnetic field in the ionosphere, and it grows with increasing solar zenith angle and is not the same in the northern and southern hemispheres, which may be due to the asymmetry of the residual magnetic field of the Martian crust. In general, one can even distinguish three populations of high-energy electrons with different temperature profiles. The magnetic field also affects the horizontal distribution of ions: streams of high-energy particles are formed above magnetic anomalies, swirling along the field lines, which increases the ionization intensity, and an increased ion density and local structures are observed.

At an altitude of 200-230 km, there is the upper boundary of the thermosphere - the exobase, above which the exosphere Mars. It consists of light substances - hydrogen, carbon, oxygen - which appear as a result of photochemical reactions in the underlying ionosphere, for example, dissociative recombination of O 2 + with electrons. The continuous supply of atomic hydrogen to the upper atmosphere of Mars occurs due to the photodissociation of water vapor near the Martian surface. Due to the very slow decrease in hydrogen concentration with height, this element is the main component of the outermost layers of the planet's atmosphere and forms a hydrogen corona that extends over a distance of about 20,000 km, although there is no strict boundary, and particles from this region simply gradually dissipate into the surrounding outer space.

In the atmosphere of Mars, it is also sometimes released chemosphere- a layer where photochemical reactions take place, and since, due to the lack of an ozone screen, like that of the Earth, ultraviolet radiation reaches the very surface of the planet, they are possible even there. The Martian chemosphere extends from the surface to an altitude of about 120 km.

Chemical composition of the lower atmosphere

Despite the strong rarefaction of the Martian atmosphere, the concentration of carbon dioxide in it is about 23 times greater than in the earth.

• Nitrogen (2.7%) is currently actively dissipating into space. In the form of a diatomic molecule, nitrogen is stably held by the attraction of the planet, but is split by solar radiation into single atoms, easily leaving the atmosphere.
• Argon (1.6%) is represented by the relatively dissipation-resistant heavy isotope argon-40. Light 36 Ar and 38 Ar are present only in parts per million
• Other noble gases: neon, krypton, xenon (ppm)
• Carbon monoxide (CO) - is a product of photodissociation of CO 2 and is 7.5⋅10 -4 concentration of the latter - this is an inexplicably small value, since the reverse reaction CO + O + M → CO 2 + M is prohibited, and much more should have accumulated CO. Various theories have been proposed for how carbon monoxide can still be oxidized to carbon dioxide, but they all have one or another drawback.
• Molecular oxygen (O 2) - appears as a result of photodissociation of both CO 2 and H 2 O in the upper atmosphere of Mars. In this case, oxygen diffuses into the lower layers of the atmosphere, where its concentration reaches 1.3⋅10 -3 of the near-surface concentration of CO 2 . Like Ar, CO, and N 2 , it is a non-condensable substance on Mars, so its concentration also undergoes seasonal variations. In the upper atmosphere, at a height of 90-130 km, the content of O 2 (share relative to CO 2) is 3-4 times higher than the corresponding value for the lower atmosphere and averages 4⋅10 -3 , varying in the range from 3.1⋅10 -3 to 5.8⋅10 -3 . In ancient times, the atmosphere of Mars contained, however, a larger amount of oxygen, comparable to its share on the young Earth. Oxygen, even in the form of individual atoms, no longer dissipates as actively as nitrogen, due to its greater atomic weight, which allows it to accumulate.
• Ozone - its amount varies greatly depending on surface temperature: it is minimal at the time of the equinox at all latitudes and maximal at the pole, where winter is, moreover, inversely proportional to the concentration of water vapor. There is one pronounced ozone layer at an altitude of about 30 km and another between 30 and 60 km.
• Water. The content of H 2 O in the atmosphere of Mars is about 100-200 times less than in the atmosphere of the driest regions of the Earth, and averages 10-20 microns of a precipitated water column. Water vapor concentration undergoes significant seasonal and diurnal variations. The degree of air saturation with water vapor is inversely proportional to the content of dust particles, which are condensation centers, and in some areas (in winter, at an altitude of 20-50 km), steam was recorded, the pressure of which exceeds the saturated vapor pressure by 10 times - much more than in the earth's atmosphere .
• Methane. Since 2003, there have been reports of registration of methane emissions of an unknown nature, but none of them can be considered reliable due to certain shortcomings in the registration methods. In this case, we are talking about extremely small values ​​- 0.7 ppbv (upper limit - 1.3 ppbv) as a background value and 7 ppbv for episodic bursts, which is on the verge of resolution. Since, along with this, information was also published about the absence of CH 4 confirmed by other studies, this may indicate some intermittent source of methane, as well as the existence of some mechanism for its rapid destruction, while the duration of the photochemical destruction of this substance is estimated at 300 years. The discussion on this issue is currently open, and it is of particular interest in the context of astrobiology, in view of the fact that on Earth this substance has a biogenic origin.
• Traces of some organic compounds. The most important are the upper limits on H 2 CO, HCl and SO 2, which indicate the absence, respectively, of reactions involving chlorine, as well as volcanic activity, in particular, the non-volcanic origin of methane, if its existence is confirmed.

The composition and pressure of the atmosphere of Mars make it impossible for humans and other terrestrial organisms to breathe. To work on the surface of the planet, a space suit is needed, although not as bulky and protected as for the Moon and outer space. The atmosphere of Mars itself is not poisonous and consists of chemically inert gases. The atmosphere somewhat slows down meteorite bodies, so there are fewer craters on Mars than on the Moon and they are less deep. And micrometeorites burn out completely, not reaching the surface.

Water, clouds and precipitation

Low density does not prevent the atmosphere from forming large-scale phenomena that affect climate.

Water vapor in the Martian atmosphere is no more than a thousandth of a percent, however, according to the results of recent (2013) studies, this is still more than previously thought, and more than in the upper layers of the Earth's atmosphere, and at low pressure and temperature, it is in a state close to saturation, so it often gathers in clouds. As a rule, water clouds form at altitudes of 10-30 km above the surface. They are concentrated mainly on the equator and are observed almost throughout the year. Clouds observed at high levels of the atmosphere (more than 20 km) are formed as a result of CO 2 condensation. The same process is responsible for the formation of low (at an altitude of less than 10 km) clouds in the polar regions in winter, when the atmospheric temperature drops below the freezing point of CO 2 (-126 ° C); in summer, similar thin formations are formed from ice H 2 O

• One of the interesting and rare atmospheric phenomena on Mars was discovered ("Viking-1") when photographing the northern polar region in 1978. These are cyclonic structures that are clearly identified in photographs by vortex-like cloud systems with counterclockwise circulation. They were found in the latitudinal zone 65-80°N. sh. during the "warm" period of the year, from spring to early autumn, when the polar front is established here. Its occurrence is due to the sharp contrast in surface temperatures at this time of year between the edge of the ice cap and the surrounding plains. The wave movements of air masses associated with such a front lead to the appearance of cyclonic eddies so familiar to us on Earth. The systems of vortex clouds found on Mars vary in size from 200 to 500 km, their speed is about 5 km/h, and the wind speed at the periphery of these systems is about 20 m/s. The duration of existence of an individual cyclonic eddy ranges from 3 to 6 days. The temperature values ​​in the central part of the Martian cyclones indicate that the clouds are composed of water ice crystals.

  Snow has indeed been observed more than once. So, in the winter of 1979, a thin layer of snow fell in the Viking-2 landing area, which lay for several months.

  Dust storms and dust devils

  A characteristic feature of the atmosphere of Mars is the constant presence of dust; according to spectral measurements, the size of dust particles is estimated at 1.5 µm. Low gravity allows even rarefied air flows to raise huge clouds of dust to a height of up to 50 km. And the winds, which are one of the manifestations of the temperature difference, often blow over the surface of the planet (especially in late spring - early summer in the southern hemisphere, when the temperature difference between the hemispheres is especially sharp), and their speed reaches 100 m / s. Thus, extensive dust storms are formed, which have long been observed in the form of individual yellow clouds, and sometimes in the form of a continuous yellow veil covering the entire planet. Most often, dust storms occur near the polar caps, their duration can reach 50-100 days. Weak yellow haze in the atmosphere, as a rule, is observed after large dust storms and is easily detected by photometric and polarimetric methods.

  Dust storms, which were well observed on images taken from orbiters, turned out to be barely visible when photographed from landers. The passage of dust storms at the landing sites of these space stations was recorded only by a sharp change in temperature, pressure, and a very slight darkening of the general sky background. The layer of dust that settled after the storm in the vicinity of the Viking landing sites amounted to only a few micrometers. All this indicates a rather low bearing capacity of the Martian atmosphere.

  From September 1971 to January 1972, a global dust storm took place on Mars, which even prevented photographing the surface from the Mariner 9 probe. The mass of dust in the atmospheric column (with an optical thickness of 0.1 to 10) estimated during this period ranged from 7.8⋅10 -5 to 1.66⋅10 -3 g/cm 2 . Thus, the total weight of dust particles in the Martian atmosphere during the period of global dust storms can reach up to 10 8 - 10 9 tons, which is commensurate with the total amount of dust in the Earth's atmosphere.

  • The aurora was first recorded by the SPICAM UV spectrometer aboard the Mars Express spacecraft. Then it was repeatedly observed by the MAVEN apparatus, for example, in March 2015, and in September 2017, a much more powerful event was recorded by the Radiation Assessment Detector (RAD) on the Curiosity rover. An analysis of the MAVEN data also revealed auroras of a fundamentally different type - diffuse, which occur at low latitudes, in areas that are not tied to magnetic field anomalies and are caused by the penetration of particles with very high energy, about 200 keV, into the atmosphere.

    In addition, the extreme ultraviolet radiation of the Sun causes the so-called own  glow of the atmosphere (eng. airglow).

    The registration of optical transitions during auroras and intrinsic glow provides important information about the composition of the upper atmosphere, its temperature, and dynamics. Thus, the study of the γ- and δ-bands of nitric oxide emission during the night period helps to characterize the circulation between the illuminated and unilluminated regions. And registration of radiation at a frequency of 130.4 nm with its own glow helped to reveal the presence of high-temperature atomic oxygen, which was an important step in understanding the behavior of atmospheric exospheres and coronas in general.

    Color

    The dust particles that fill the Martian atmosphere are mostly iron oxide, and it gives it a reddish-orange tint.

    According to measurements, the atmosphere has an optical thickness of 0.9, which means that only 40% of the incident solar radiation reaches the surface of Mars through its atmosphere, and the remaining 60% is absorbed by dust hanging in the air. Without it, the Martian skies would have approximately the same color as the earth's sky at an altitude of 35 kilometers. It should be noted that in this case the human eye would adapt to these colors, and the white balance would automatically be adjusted so that the sky would be seen the same as under terrestrial lighting conditions.

    The color of the sky is very heterogeneous, and in the absence of clouds or dust storms from a relatively light on the horizon, it darkens sharply and in a gradient towards the zenith. In a relatively calm and windless season, when there is less dust, the sky can be completely black at the zenith.

    Nevertheless, thanks to the images of the rovers, it became known that at sunset and sunrise around the Sun, the sky turns blue. The reason for this is Rayleigh scattering - light is scattered on gas particles and colors the sky, but if on a Martian day the effect is weak and invisible to the naked eye due to rarefied atmosphere and dust, then at sunset the sun shines through a much thicker layer of air, due to which blue and violet begin to scatter components. The same mechanism is responsible for the blue sky on Earth during the day and yellow-orange at sunset. [ ]

    A panorama of the Rocknest sand dunes, compiled from images from the Curiosity rover.

    Changes

    Changes in the upper layers of the atmosphere are quite complex, since they are connected with each other and with the underlying layers. Atmospheric waves and tides propagating upward can have a significant effect on the structure and dynamics of the thermosphere and, as a consequence, the ionosphere, for example, the height of the upper boundary of the ionosphere. During dust storms in the lower atmosphere, its transparency decreases, it heats up and expands. Then the density of the thermosphere increases - it can vary even by an order of magnitude - and the height of the electron concentration maximum can rise by up to 30 km. Changes in the upper atmosphere caused by dust storms can be global, affecting areas up to 160 km above the planet's surface. The response of the upper atmosphere to these phenomena takes several days, and it returns to its previous state much longer - several months. Another manifestation of the relationship between the upper and lower atmosphere is that water vapor, which, as it turned out, is oversaturated with the lower atmosphere, can undergo photodissociation into lighter H and O components, which increase the density of the exosphere and the intensity of water loss by the Martian atmosphere. External factors causing changes in the upper atmosphere are the Sun's extreme ultraviolet and soft X-ray radiation, solar wind particles, cosmic dust, and larger bodies such as meteorites. The task is complicated by the fact that their impact, as a rule, is random, and its intensity and duration cannot be predicted, moreover, episodic phenomena are superimposed by cyclical processes associated with changes in the time of day, season, and also the solar cycle. At present, at best, there is accumulated statistics of events on the dynamics of atmospheric parameters, but a theoretical description of the regularities has not yet been completed. A direct proportionality between the concentration of plasma particles in the ionosphere and solar activity has been definitely established. This is confirmed by the fact that a similar regularity was actually recorded according to the results of observations in 2007-2009 for the Earth's ionosphere, despite the fundamental difference in the magnetic field of these planets, which directly affects the ionosphere. And ejections of particles of the solar corona, causing a change in the pressure of the solar wind, also entail a characteristic compression of the magnetosphere and ionosphere: the maximum plasma density drops to 90 km.

    Daily fluctuations

    Despite its rarefaction, the atmosphere nevertheless reacts to changes in the solar heat flux more slowly than the surface of the planet. So, in the morning period, the temperature varies greatly with height: a difference of 20 ° was recorded at a height of 25 cm to 1 m above the surface of the planet. With the rising of the Sun, cold air heats up from the surface and rises in the form of a characteristic swirl upwards, raising dust into the air - this is how dust devils are formed. In the near-surface layer (up to 500 m high) there is a temperature inversion. After the atmosphere has already warmed up by noon, this effect is no longer observed. The maximum is reached at about 2 o'clock in the afternoon. The surface then cools faster than the atmosphere and a reverse temperature gradient is observed. Before sunset, the temperature again decreases with height.

    The change of day and night also affects the upper atmosphere. First of all, ionization by solar radiation stops at night, however, the plasma continues to be replenished for the first time after sunset due to the flow from the day side, and then is formed due to electron impacts moving downward along the magnetic field lines (the so-called electron invasion) - then the maximum observed at an altitude of 130-170 km. Therefore, the density of electrons and ions from the night side is much lower and is characterized by a complex profile, which also depends on the local magnetic field and varies in a non-trivial way, the regularity of which is not yet fully understood and described theoretically. During the day, the state of the ionosphere also changes depending on the zenith angle of the Sun.

    annual cycle

    Like on Earth, on Mars there is a change of seasons due to the tilt of the axis of rotation to the plane of the orbit, so in winter the polar cap grows in the northern hemisphere, and almost disappears in the southern, and after six months the hemispheres change places. At the same time, due to the rather large eccentricity of the planet's orbit at perihelion (winter solstice in the northern hemisphere), it receives up to 40% more solar radiation than in aphelion, and in the northern hemisphere, winter is short and relatively moderate, and summer is long, but cool, in in the south, on the contrary, summers are short and relatively warm, and winters are long and cold. In this regard, the southern cap in winter grows up to half the pole-equator distance, and the northern cap only up to a third. When summer comes at one of the poles, carbon dioxide from the corresponding polar cap evaporates and enters the atmosphere; the winds carry it to the opposite cap, where it freezes again. In this way, the carbon dioxide cycle occurs, which, along with the different sizes of the polar caps, causes a change in the pressure of the Martian atmosphere as it orbits the Sun. Due to the fact that in winter up to 20-30% of the entire atmosphere freezes in the polar cap, the pressure in the corresponding area drops accordingly.

    Seasonal variations (as well as daily ones) also undergo water vapor concentration - they are in the range of 1-100 microns. So, in winter the atmosphere is almost “dry”. Water vapor appears in it in the spring, and by mid-summer its amount reaches a maximum, following changes in surface temperature. During the summer-autumn period, water vapor is gradually redistributed, and its maximum content moves from the northern polar region to equatorial latitudes. At the same time, the total global vapor content in the atmosphere (according to Viking-1 data) remains approximately constant and is equivalent to 1.3 km 3 of ice. The maximum content of H 2 O (100 μm of precipitated water, equal to 0.2 vol%) was recorded in summer over the dark region surrounding the northern residual polar cap - at this time of the year the atmosphere above the ice of the polar cap is usually close to saturation.

    In the spring-summer period in the southern hemisphere, when dust storms are most actively formed, diurnal or semidiurnal atmospheric tides are observed - an increase in pressure near the surface and thermal expansion of the atmosphere in response to its heating.

    The change of seasons also affects the upper atmosphere - both the neutral component (thermosphere) and the plasma (ionosphere), and this factor must be taken into account together with the solar cycle, and this complicates the task of describing the dynamics of the upper atmosphere.

    Long term change

    see also

    Notes

    1. Williams, David R. Mars Fact Sheet (indefinite) . National Space Science Data Center. NASA (September 1, 2004). Retrieved 28 September 2017.
    2. N. Mangold, D. Baratoux, O. Witasse, T. Encrenaz, C. Sotin. Mars: a small terrestrial planet : [English] ]// The Astronomy and Astrophysics Review. - 2016. - V. 24, No. 1 (December 16). - P. 15. - DOI: 10.1007/s00159-016-0099-5.
    3. Atmosphere of Mars (indefinite) . UNIVERSE-PLANET // PORTAL TO ANOTHER DIMENSION
    4. Mars is a red star. Description of the area. Atmosphere and climate (indefinite) . galspace.ru - Solar System Exploration Project. Retrieved 29 September 2017.
    5. (English) Out of Thin Martian Air Astrobiology Magazine, Michael Schirber, 22 August 2011.
    6. Maxim Zabolotsky. General information about atmosphere Mars (indefinite) . spacegid.com(21.09.2013). Retrieved 20 October 2017.
    7. Mars Pathfinder - Science  Results - Atmospheric and Meteorological Properties (indefinite) . nasa.gov. Retrieved April 20, 2017.
    8. J. L. Fox, A. Dalgarno. Ionization, luminosity, and heating of the upper atmosphere of Mars: [English] ]// J Geophys Res. - 1979. - T. 84, issue. A12 (December 1). - S. 7315–7333. -

Mars, like Venus, are Earth-like planets. They have a lot in common, but there are also differences. Scientists do not lose hope of finding life on Mars, as well as terraforming this "relative" of the Earth, albeit in the distant future. For the Red Planet, this task looks easier than for Venus. Unfortunately, Mars has a very weak magnetic field, which complicates matters. The fact is that due to the almost complete absence of a magnetic field, the solar wind has a very strong influence on the atmosphere of the planet. It causes dissipation of atmospheric gases, so that about 300 tons of atmospheric gases go into space per day.

According to experts, it was the solar wind that caused the dispersion of about 90% of the Martian atmosphere over billions of years. As a result, the pressure at the surface of Mars is 0.7-1.155 kPa (1/110 of the earth's, such pressure on Earth can be seen by rising to a height of thirty kilometers from the surface).

The atmosphere on Mars consists mainly of carbon dioxide (95%) with small admixtures of nitrogen, argon, oxygen and some other gases. Unfortunately, the pressure and composition of the atmosphere on the Red Planet makes it impossible for terrestrial living organisms to breathe on the Red Planet. Probably, some microscopic organisms will be able to survive, but they will not be able to feel comfortable in such conditions.

The composition of the atmosphere is not such a problem. If the atmospheric pressure on Mars were half or a third of that of the earth, then the colonists or marsonauts could be at certain times of the day and year on the surface of the planet without spacesuits, using only a breathing apparatus. Many terrestrial organisms would also feel more comfortable on Mars.

NASA believes that it is possible to increase the pressure of the atmosphere on Earth's neighbor if Mars is protected from the solar wind. This protection is provided by a magnetic field. On Earth, it exists due to the so-called hydrodynamic dynamo mechanism. In the liquid core of the planet, streams of an electrically conductive substance (molten iron) are constantly circulating, due to which electric currents are excited, which create magnetic fields. The internal flows in the core of the earth are asymmetric, which leads to an increase in the magnetic field. The Earth's magnetosphere reliably protects the atmosphere from "blowing out" by the solar wind.

The dipole, according to the calculations of the authors of the project to create a magnetic shield for Mars, will generate a sufficiently strong magnetic field that will not allow the solar wind to reach the planet.

Unfortunately for humans, there is no constant strong magnetic field on Mars (and Venus), only weak traces are recorded. Thanks to the Mars Global Surveyor, it was possible to detect magnetic material under the crust of Mars. NASA believes that these anomalies were formed under the influence of the once magnetic core and retained their magnetic properties even after the planet itself lost its field.

Where to get a magnetic shield

NASA Science Director Jim Green believes that the natural magnetic field of Mars cannot be restored, in any case, now or even in the very distant future, humanity cannot afford it. But you can create an artificial field. True, not on Mars itself, but next to it. Speaking on "The Future of the Mars Environment for Research and Science" at the Planetary Science Vision 2050 Workshop, Greene proposed the creation of a magnetic shield. This shield, Mars L1, as conceived by the authors of the project, will close Mars from the solar wind, and the planet will begin to restore its atmosphere. It is planned to place the shield between Mars and the Sun, where it would be in a stable orbit. It is planned to create a field using a huge dipole or two equal and oppositely charged magnets.

NASA diagram shows how a magnetic shield will protect Mars from the effects of the solar wind

The authors of the idea created several simulation models, each of which showed that during the launch of the magnetic shield, the pressure on Mars would reach half that of the Earth. In particular, carbon dioxide at the poles of Mars will evaporate, passing into gas from the solid phase. Over time, the greenhouse effect will manifest itself, on Mars it will begin to warm up, the ice that is close to the surface of the planet in many of its places will melt and the planet will be covered with water. It is believed that such conditions existed on Mars about 3.5 billion years ago.

Of course, this is not a project of today, but perhaps in the next century people will be able to realize this idea and terraform Mars, creating a second home for themselves.

Today, not only science fiction writers in their stories, but also real scientists, businessmen, and politicians talk about flights to Mars and its possible colonization. Probes and rovers gave answers about the features of geology. However, for manned missions, one should find out whether Mars has an atmosphere and what its structure is.

General information

Mars has its own atmosphere, but it is only 1% of Earth's. Like Venus, it is predominantly carbon dioxide, but again, much thinner. The relatively dense layer is 100 km (for comparison, the Earth has 500-1000 km, according to various estimates). Because of this, there is no protection from solar radiation, and the temperature regime is practically not regulated. There is no air on Mars in the usual sense.

Scientists have established the exact composition:

• Carbon dioxide - 96%.
• Argon - 2.1%.
• Nitrogen - 1.9%.

Methane was discovered in 2003. The discovery spurred interest in the Red Planet, with many countries launching exploration programs that led to talk of flight and colonization.

Due to the low density, the temperature regime is not regulated, therefore, the differences are on average 100 0 C. In the daytime, quite comfortable conditions of +30 0 C are established, and at night the surface temperature drops to -80 0 C. The pressure is 0.6 kPa (1 /110 from the earth indicator). On our planet, similar conditions are found at an altitude of 35 km. This is the main danger for a person without protection - he will not be killed by temperature or gases, but by pressure.

There is always dust on the surface. Due to the low gravity, the clouds rise up to 50 km. Strong temperature drops lead to the appearance of winds with gusts up to 100 m / s, so dust storms on Mars are common. They do not pose a serious threat due to the small concentration of particles in the air masses.

What are the layers of the atmosphere of Mars?

The force of gravity is less than Earth's, so the atmosphere of Mars is not so clearly divided into layers in terms of density and pressure. The homogeneous composition is preserved up to the mark of 11 km, then the atmosphere begins to separate into layers. Above 100 km, the density decreases to the minimum values.

• Troposphere - up to 20 km.
• Stratomesosphere - up to 100 km.
• Thermosphere - up to 200 km.
• Ionosphere - up to 500 km.

In the upper atmosphere there are light gases - hydrogen, carbon. Oxygen accumulates in these layers. Individual particles of atomic hydrogen propagate over a distance of up to 20,000 km, forming a hydrogen corona. There is no clear separation between the extreme regions and outer space.

upper atmosphere

At a mark of more than 20-30 km, the thermosphere is located - the upper regions. The composition remains stable up to an altitude of 200 km. There is a high content of atomic oxygen. The temperature is quite low - up to 200-300 K (from -70 to -200 0 C). Next comes the ionosphere, in which ions react with neutral elements.

lower atmosphere

Depending on the season, the boundary of this layer changes, and this zone is called the tropopause. Further on, the stratomesosphere extends, the average temperature of which is -133 0 C. On Earth, ozone is contained here, which protects against cosmic radiation. On Mars, it accumulates at an altitude of 50-60 km and then is practically absent.

Composition of the atmosphere

The earth's atmosphere consists of nitrogen (78%) and oxygen (20%), argon, carbon dioxide, methane, etc. are present in small quantities. Such conditions are considered optimal for the emergence of life. The composition of the air on Mars is very different. The main element of the Martian atmosphere is carbon dioxide - about 95%. Nitrogen accounts for 3%, and argon 1.6%. The total amount of oxygen is not more than 0.14%.

This composition was formed due to the weak attraction of the Red Planet. The most stable was heavy carbon dioxide, which is constantly replenished as a result of volcanic activity. Light gases dissipate in space due to low gravity and the absence of a magnetic field. Nitrogen is held by gravity as a diatomic molecule, but splits under the influence of radiation, and in the form of single atoms flies into space.

The situation is similar with oxygen, but in the upper layers it reacts with carbon and hydrogen. However, scientists do not fully understand the features of the reactions. According to calculations, the amount of carbon monoxide CO should be greater, but in the end it oxidizes to carbon dioxide CO2 and sinks to the surface. Separately, molecular oxygen O2 appears only after the chemical decomposition of carbon dioxide and water in the upper layers under the influence of photons. It refers to non-condensable substances on Mars.

Scientists believe that millions of years ago, the amount of oxygen was comparable to the earth's - 15-20%. It is not yet known exactly why conditions have changed. However, individual atoms do not volatilize as actively, and due to the greater weight, it even accumulates. To some extent, the reverse process is observed.

Other important elements:

• Ozone is practically absent, there is one area of ​​accumulation 30-60 km from the surface.
• Water content is 100-200 times less than in the driest region of the Earth.
• Methane - emissions of an unknown nature are observed, and so far the most discussed substance for Mars.

Methane on Earth belongs to biogenic substances, therefore, it can potentially be associated with organic matter. The nature of the appearance and rapid destruction has not yet been explained, so scientists are looking for answers to these questions.

What happened to the atmosphere of Mars in the past?

Over the millions of years of the existence of the planet, the atmosphere changes in composition and structure. As a result of the research, evidence has emerged that liquid oceans existed on the surface in the past. However, now the water remains in small quantities in the form of steam or ice.

Reasons for the disappearance of fluid:

• Low atmospheric pressure is not able to keep water in a liquid state for a long time, as it happens on Earth.
• Gravity is not strong enough to hold vapor clouds.
• Due to the absence of a magnetic field, matter is carried away by particles of the solar wind into space.
• With significant temperature fluctuations, water can only be stored in a solid state.

In other words, the Martian atmosphere is not dense enough to hold water as a liquid, and the small force of gravity is not able to hold hydrogen and oxygen.
According to experts, favorable conditions for life on the Red Planet could have formed about 4 billion years ago. Perhaps there was life at that time.

The following causes of destruction are called:

• Lack of protection from solar radiation and gradual depletion of the atmosphere over millions of years.
• A collision with a meteorite or other cosmic body that instantly destroyed the atmosphere.

The first reason is currently more likely, since no traces of a global catastrophe have yet been found. Similar conclusions were made thanks to the study of the autonomous station Curiosity. The rover has established the exact composition of the air.

The ancient atmosphere of Mars contained a lot of oxygen

Today, scientists have little doubt that there used to be water on the Red Planet. On numerous views of the outlines of the oceans. Visual observations are supported by specific studies. The rovers took soil samples in the valleys of the former seas and rivers, and the chemical composition confirmed the initial assumptions.

Under current conditions, any liquid water on the planet's surface will instantly evaporate because the pressure is too low. However, if in ancient times there were oceans and lakes, then the conditions were different. One of the assumptions is a different composition with an oxygen fraction of the order of 15-20%, as well as an increased proportion of nitrogen and argon. In this form, Mars becomes almost identical to our home planet - with liquid water, oxygen and nitrogen.

Other scientists suggest the existence of a full-fledged magnetic field that can protect against the solar wind. Its power is comparable to that of the earth, and this is another factor that speaks in favor of the presence of conditions for the origin and development of life.

Causes of Atmosphere Depletion

The peak of development falls on the Hesperian era (3.5-2.5 billion years ago). On the plain was a salty ocean comparable in size to the Arctic Ocean. The surface temperature reached 40-50 0 C, and the pressure was about 1 atm. There is a high probability of the existence of living organisms in that period. However, the period of "prosperity" was not long enough for a complex and even more intelligent life to arise.

One of the main reasons is the small size of the planet. Mars is smaller than Earth, so gravity and magnetic field are weaker. As a result, the solar wind actively knocked out the particles and literally cut off the shell layer by layer. The composition of the atmosphere began to change over 1 billion years, after which climate change became catastrophic. The decrease in pressure led to the evaporation of the liquid and temperature drops.

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).

Prior to landing on the Martian surface of the landers, 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 bowl-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 the spreading of melt water and the growth of vegetation. 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 descended 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 struck again on the surface 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 a book by Percival Lowell 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 somewhat facilitate the fulfillment of this task. 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.