> Terrestrial planets

Planets terrestrial group - the first four planets Solar system with photo. Find out the characteristics and description of the planets terrestrial, search for exoplanets, research.

Researchers have been studying the vastness of the solar system for centuries, noting various planetary types. Since the opening of access to exoplanets, our information base has become even wider. In addition to gas giants, we also found terrestrial objects. What is this?

Definition of the Terrestrial planets

Terrestrial planet- a celestial body, represented by silicate rocks or metal, and has a hard surface layer. This is the main difference from the gas-filled gas giants. The term is taken from the Latin word "Terra", which translates as "Earth". Below is a list showing which terrestrial planets are.

The structure and features of the terrestrial planets

All bodies are endowed with a similar structure: a core of metal, filled with iron and surrounded by a mantle of silicates. Their surface sphere is covered with craters, volcanoes, mountains, canyons and other formations.

There are secondary atmospheres created by volcanic activity or the arrival of comets. They have few or no satellites. The Earth has the Moon, and Mars has Phobos and Deimos. Not endowed with ring systems. Let's see what the characteristics of the terrestrial planets look like, and also notice what are their similarities and differences using the example of Mercury, Venus, Earth and Mars.

Basic facts of the terrestrial planets

Mercury- the smallest planet in the system, reaching 1/3 of the earth's size. Endowed with a thin atmospheric layer, which is why it constantly freezes and heats up. It is characterized by high density with iron and nickel. The magnetic field reaches only 1% of the earth's. On the surface, there are many deep crater scars and a weak layer of silicate particles. In 2012, traces of organic material were noticed. These are the building blocks for life and also found water ice.

Venus it is similar in size to Earth, but its atmosphere is too dense and overflowing with carbon monoxide. Because of this, heat is trapped on the planet, making it the hottest in the system. Most of the surface is home to active volcanoes and deep canyons. Only a few devices managed to penetrate the surface and survive for a short period of time. Craters are few because the meteors burn out.

Earth- the largest in the terrestrial type and has a huge amount of liquid water. It is needed for a life that develops in all forms. There is a rocky surface sheltered by canyons and hills, as well as a heavy metal core. The atmosphere contains water vapor, which helps to soften the daily temperature regime. There is a change of regular seasons. The greatest heating goes to areas near the equatorial line. But now the numbers are rising due to human activity.

Mars has the highest mountain in the solar system. Most of the surface is represented by ancient sediments and crater formations. But you can also find younger sites. There are polar caps that shrink in size in the summer and spring. It is inferior in density to the Earth, and the core is solid. Researchers have not yet found evidence of life, but there are all hints and conditions in the past. The planet has water ice, organic matter and methane.

Formation and general features of the terrestrial planets

It is believed that the terrestrial planets appeared first. Initially, the dust particles merged to create large objects. They were located closer to the Sun, so the volatiles evaporated. Celestial objects grew up to kilometers in size, becoming planetesimals. Then they accumulate more and more dust.

Analysis shows that at an early stage in the development of the solar system, about a hundred protoplanets, whose sizes varied between the Moon and Mars, could have been present. They constantly collided, due to which they merged, throwing out debris. As a result, 4 large terrestrial planets survived: Mercury, Venus, Mars and Earth.

All of them are distinguished by a high density index, and the composition is represented by silicates and metallic iron. The largest representative of the terrestrial type is the Earth. These planets also stand out overall structure structures, including the core, mantle and crust. Only two planets (Earth and Mars) have satellites.

Ongoing exploration of the terrestrial planets

Researchers believe that terrestrial planets are the best candidates for detecting life. Of course, the conclusions are based on the fact that the only planet with life is Earth, so its characteristics and features serve as a kind of benchmark.

Everything suggests that life is able to survive in extreme conditions. Therefore, it is expected to be found even on Mercury and Venus, despite their high temperatures. Most of all attention is paid to Mars. It is not only the main candidate for finding life, but also a potential future colony.

If everything goes according to plan, then in the 2030s. the first batch of astronauts may be sent to the Red Planet. Now on the planet there are constantly rovers and orbiters looking for water and signs of life.

Terrestrial exoplanets

Many of the exoplanets found turned out to be gas giants, because they are much easier to find. But since 2005, we began to actively capture terrestrial objects thanks to the Kepler mission. Most have been nicknamed the super-land class.

Among these, it is worth remembering Gliese 876d, whose mass is 7-9 times that of the earth. It orbits a red dwarf, 15 light years distant from us. In the Gliese 581 system, 3 terrestrial exoplanets were found with a distance of 20 light years.

The smallest is Gliese 581e. It exceeds our mass by only 1.9 times, but is located extremely close to its star. The first confirmed terrestrial exoplanet was Kepler-10b, 3-4 times larger than our mass. It is 460 light years distant and was found in 2011. At the same time, the mission team issued a list of 1235 applicants, where 6 were terrestrial and located in the habitable zone.

Super Earth

Among exoplanets, it was possible to find many super-lands (in size between Earth and Neptune). This species cannot be found on the territory of our system, therefore it is not yet clear whether they look more like giants or the terrestrial type.

Now scientific world is awaiting the launch of the James Webb Telescope, which promises to increase the power of search and reveal to us the depths of space.

Categories of terrestrial planets

There is a division of the terrestrial planets. Silicate - typical objects of our system, represented by a stone mantle and a metal core. Iron - a theoretical variety, consisting entirely of iron. This gives more density but shorter radius. Such planets can appear only in areas with a high temperature index.

Rocky is another theoretical species where there is silicate rock but no metal core. They should form further away from the star. Carbonaceous - endowed with a metal core, around which a carbonaceous mineral has accumulated.

The study of the planets is carried out both with the help of ground-based astronomical instruments installed in observatories, and with the help of spacecraft.

Planet Earth

Numerous photographs of the Earth taken from spacecraft make it possible to see the three main shells the globe: the atmosphere and its clouds, the hydrosphere and the lithosphere with its natural covers. The majority of the planets of the solar system have an atmosphere; a hard shell is characteristic of the terrestrial planets, satellites of planets and asteroids. The hydrosphere of the Earth is a unique phenomenon in the solar system, none of the known planets has it. Indeed, for the existence of water in liquid form, certain conditions are needed: temperature and pressure. Water is very common chemical compound in the Universe, but on other celestial bodies we meet with water mainly in its solid phase, known on Earth as snow, frost and ice. The crust is very thin: from 10 km under the oceans to 80 km under the mountain ranges. The core has a radius half the radius of the planet, and between the core and the crust there is an intermediate layer - the Earth's mantle, consisting of substances denser than in the crust.
Gas envelope - the atmosphere surrounding the Earth, contains 78% nitrogen, 21% oxygen and a negligible amount of other gases.
The lower layer of the atmosphere is called the troposphere, which extends to an altitude of 10-12 km (at mid-latitudes). In it, with increasing altitude, the temperature drops. Above, in the stratosphere, it remains almost constant, about -40 ° C. From an altitude of about 25 km, the temperature of the earth's atmosphere slowly rises due to absorption ultraviolet radiation The sun.
The atmosphere reflects or absorbs most of the radiation coming to Earth from outer space. For example, it does not transmit X-rays from the Sun. The atmosphere protects us from the continuous bombardment by micrometeorites, and from the destructive action of cosmic rays - streams of "rapidly flying particles (mainly protons and nuclei of helium atoms).

The atmosphere is playing crucial role v heat balance Earth. Visible solar radiation can pass through it with almost no attenuation. It is absorbed ground surface, which at the same time heats up and emits infrared rays. The earth's magnetic field is quite large (about 5 x 10 -5 T). With distance from the Earth, the magnetic induction weakens.

moon

The origin of the moon has not yet been conclusively established. The most developed are three different hypotheses. V late XIX v. J. Darwin put forward a hypothesis according to which the Moon and the Earth originally constituted one common molten mass, the speed of rotation of which increased as it cooled and contracted; As a result, this mass was torn into two parts: a large one - the Earth and a smaller one - the Moon. This hypothesis explains the low density of the Moon, formed from the outer layers of the original mass. However, it meets with serious objections from the point of view of the mechanism of such a process; in addition, there are significant geochemical differences between the rocks of the earth's shell and lunar rocks.
THE MOON is the only natural satellite of the Earth and the closest celestial body to us; the average distance to the moon is 384,000 kilometers.
The moon moves around the Earth at an average speed of 1.02 km / s in an approximately elliptical orbit in the same direction as the vast majority of other bodies in the solar system, that is, counterclockwise, if you look at the moon's orbit from the side North Pole the world. The semi-major axis of the Moon's orbit, equal to the average distance between the centers of the Earth and the Moon, is 384 400 km (approximately 60 Earth radii). The period of the Moon's revolution around the Earth, the so-called sidereal (sidereal) month, is 27.32166 days. The shape of the moon is very close to a ball with a radius of 1737 km, which is equal to 0.2724 of the equatorial radius of the Earth. The mass of the moon is most accurately determined from observations of its artificial satellites... It is 81 times less than the mass of the Earth. The average density of the Moon is 3.34 g / cm 3 (0.61 of the Earth's average density). The acceleration of gravity on the lunar surface is 6 times less than on Earth.

Relief of the lunar surface

The relief of the lunar surface was mainly clarified as a result of many years of telescopic observations. " Lunar seas", occupying about 40% of the visible surface of the Moon, are flat lowlands crossed by cracks and low winding ramparts. Many seas are surrounded by concentric ring ridges. The rest, lighter surface is covered with numerous craters, ring-shaped ridges, furrows, etc. Craters less than 15- 20 kilometers have a simple cup-shaped shape, larger craters (up to 200 kilometers in diameter) consist of a rounded rampart with steep inner slopes, have a relatively flat bottom, deeper than the surrounding area, often with a central hill.
Craters on the lunar surface have different relative ages: from ancient, barely distinguishable, heavily reworked formations to very clear-cut young craters, sometimes surrounded by light "rays". Due to the lack of atmosphere and hydrosphere, a significant part of these craters have survived to this day. Now meteorites fall on the moon much less frequently; volcanism also largely stopped, as the moon consumed a lot of thermal energy, and radioactive elements were carried into the outer layers of the moon.

The uppermost layer of the Moon is represented by the crust, the thickness of which, determined only in the regions of the basins, is 60 km. It is highly probable that the crust is about 1.5 times thicker on the vast continental areas of the reverse side. The crust is composed of igneous crystalline rocks - basalts. Under the crust is a mantle, in which, like the earth, you can distinguish the upper, middle and lower. Thickness top mantle about 250 km, and an average of about 500 km, and its border with the lower mantle is located at a depth of about 1000 km. In the very center, there appears to be a small liquid core with a radius of less than 350 kilometers. The core can be iron-sulphide or iron; in the latter case, it should be less, which is in better agreement with the estimates of the density distribution over depth. Its mass probably does not exceed 2% of the mass of the entire moon. The temperature in the core depends on its composition and, apparently, is in the range of 1300 - 1900 K.

Terrestrial planets

The terrestrial planets - Mercury, Venus, Earth and Mars differ from the giant planets in smaller size, less mass, higher density, slower rotation, much more rarefied atmospheres, few or no satellites.

Mercury

It is the planet closest to the Sun, slightly larger than the Moon, but its average density is almost the same as that of the Earth. Radar observations have detected the extremely slow rotation of Mercury. His sidereal day, i.e. the period of rotation around the axis relative to the stars, equal to 58.65 of our days. Solar days on this planet (that is, the time interval between successive noons) is about 176 Earth days. They are equal to two Mercurian years, since Mercury makes one revolution around the Sun in 88 Earth days.
The atmosphere on Mercury is virtually nonexistent. Therefore, its daytime hemisphere becomes very hot. At the sunflower point on Mercury, a temperature of more than 400 ° C was measured. At this temperature, lead, tin and even zinc melt. The surface of Mercury is dotted with craters in such a way that it is difficult to distinguish it from the surface of the Moon in photographs.

Venus

Venus is the same size as Earth, and its mass is more than 80% of the Earth's mass. Located closer to the Sun than our planet, Venus receives from it more than twice as much light and heat as the Earth.
Venus comes closer to Earth than any other planet. But the dense, cloudy atmosphere makes it impossible to directly see its surface. Radar images show a very wide variety of craters, volcanoes and mountains. The surface temperature is high enough to melt lead, and this planet may have once had vast oceans. Venus has an almost circular orbit, which it orbits in 225 Earth days at a distance of 108.2 million km from the Sun. Venus rotates around the axis in 243 Earth days - the maximum time among all planets. Venus rotates around its axis in the opposite direction, that is, in the direction opposite to its orbital motion. Venus is only slightly smaller in size than Earth, and its mass is almost the same. For these reasons, Venus is sometimes referred to as the twin or sister of the Earth. However, the surface and atmosphere of these two planets are completely different. There are rivers, lakes, oceans and an atmosphere on Earth that we breathe. Venus is a scorchingly hot planet with a dense atmosphere that would be fatal to humans.

Mars

Mars is half the diameter of Earth. Its orbit has significant eccentricity, so when Mars is in opposition near perihelion, it shines in the sky, second only in brightness to Venus. Such confrontations are called great and are repeated after 15 and 17 years.
The year of Mars is almost twice as long as the Earth's, there is also a change of seasons, since the axis of the daily rotation of Mars is tilted to the plane of its orbit, almost like that of the Earth.
It turned out that the planet's atmosphere is very rarefied and its pressure is about 100 times less than that of the Earth. Basically, it consists of carbon dioxide, oxygen and water vapor in it is extremely small.
Conditions on Mars are harsh. Daily temperature changes on Mars reach 80-100 ° C.
Occasionally, powerful dust storms occur on Mars, sometimes lasting for months, raising colossal amounts of the smallest dust particles into the atmosphere. Thus, the existence of sandy deserts there, which determined the orange color of Mars as a whole, is confirmed. Based on dust storms, Mars may have strong winds blowing at speeds of tens of meters per second.
Mars, like the Moon and Mercury, is dotted with craters. The shape of the Martian craters testifies to the phenomena of weathering and leveling of its surface. Several giant, apparently extinct volcanoes have been discovered on Mars. The height of the largest of them is 27 km. The magnetic field of Mars is much weaker than the earth's.

Planets are giants

The solar system is a system of celestial bodies welded together by the forces of mutual attraction. It includes: the central body of the Sun, 9 major planets with their satellites (of which more than 60 are now known), several thousand minor planets, or asteroids (over 5 thousand have been discovered, in reality there are many more), several hundred observed comets and countless meteoric bodies. Large planets are divided into two main groups: terrestrial planets - Mercury, Venus, Earth and Mars, and planets of the Jupiter group, or giant planets: Jupiter, Saturn, Uranus, Neptune. Between the orbits of Mars and Jupiter, there is a belt of minor planets - asteroids. About 2 thousand of them are well studied, their orbits are calculated, their sizes are established, and the asteroids themselves are given names. Behind the asteroid belt begins the kingdom of the giant planets. There are four of them: Jupiter, Saturn, Uranus and Neptune. The largest of these is Jupiter. In terms of volume, it is 1300 times larger than the Earth. The giant planets also have very significant masses. The mass of Jupiter is equal to 318 Earth masses, Saturn -95. All the planets of this group rotate rapidly around their axes. A day on Neptune lasts 15 hours and 48 minutes. On Jupiter - 9 hours 50 minutes. The chemical composition of the giants is mainly a hydrogen-helium base. The average density of their substance is very low. Apparently, giant planets do not have a solid surface. Moving around the giant planets big number satellites.

Table 1. Comparative characteristics Planets

Jupiter

Jupiter is surrounded by a powerful atmosphere composed mostly of hydrogen. Helium makes up about 11% of the planet's gas envelope by volume. Jupiter's mass is 318 times that of Earth. Orbiting at a speed of 13 km / s, it makes a complete revolution around the Sun in 12 Earth years. It rotates very quickly on its axis. His day is 9 hours 50 minutes. Jupiter has a strong magnetic field... This leads to the appearance of auroras in the planet's atmosphere.

Saturn

The most beautiful planet. It makes a complete revolution around the Sun in 30 Earth years. A Red Spot has been found in the atmosphere. Among the planets, Saturn stands out for its unusual appearance: it has formations - rings encircling its central core. According to theoretical calculations based on astronomical observations and data obtained using spacecraft, the internal structure has much in common with the structure of Jupiter. In the very center there is a liquid core surrounded by an outer core of CH 4, NH 3 and H 2 O. And the outer core is surrounded by a belt of metallic hydrogen.

Uranus

Uranus was discovered by the English scientist Herschel in 1781. The year on Uranus lasts 84 terrestrial years, the days are almost equal to terrestrial ones. Unlike other planets, Uranus seems to lie on its side. The axis of its rotation is located in the plane of the orbit. Uranium is composed of hydrogen and helium. But since the average density is slightly higher than the densities of Jupiter and Saturn, it can be assumed that the planet contains an increased amount of helium, or a core of heavy metals. In 1977, rings were discovered in Uranus.

Neptune

The farthest of the giant planets is Neptune. The year lasts 165 Earth years. The average density of matter in Neptune is even higher than that of Uranus, apparently, it has a core of silicates, metals and other non-metals that are part of the terrestrial planets.

Features of the structure of giant planets

The most important structural feature is that these planets do not have hard surfaces. This representation is in good agreement with low and medium densities, their chemical composition (they consist mainly of light elements - hydrogen and helium), fast zonal rotation, and some other data.

Asteroids

Small planets, or asteroids, mostly revolve between the orbits of Mars and Jupiter, and are invisible to the naked eye. The first minor planet was discovered in 1801, and by tradition it was named one of the names of Greco-Roman mythology - Ceres... Soon, other minor planets were found, named Pallas, Vesta and Juno... More than 3000 asteroids are currently known. For billions of years, asteroids have collided with each other from time to time.
The brightest asteroid - Vesta is no brighter than the 6th magnitude... Most large asteroid- Ceres. Its diameter is about 800 km. The smallest known asteroids are only about a kilometer in diameter. Of course, asteroids have no atmosphere. In the sky, small planets look like stars, which is why they were called asteroids, which translated from ancient Greek means "star-like". The orbits of some asteroids have unusually large eccentricities. As a result, at perihelion, they approach the Sun closer to Mars and Earth, and Icarus - closer than Mercury. In 1968, Icarus approached the Earth at a distance of less than 10 million kilometers, but his insignificant attraction had no effect on the Earth.

Fireballs and meteorites

A fireball is a rather rare phenomenon - a fireball flying across the sky. This phenomenon is caused by the intrusion into the dense layers of the atmosphere of large solid particles called meteoric bodies. Moving in the atmosphere, the particle heats up due to deceleration, and an extensive luminous envelope consisting of hot gases is formed around it. Fireballs often have a noticeable angular diameter and are visible even during the day.
A small meteoroid sometimes evaporates entirely in the Earth's atmosphere. In most cases, its mass greatly decreases during the flight, and only remnants reach the Earth, usually having time to cool down when the cosmic speed has already been extinguished by air resistance.
There are three types of meteorites: stone, iron and iron-stone. Sometimes meteorites are found many years after they fell. Especially many iron meteorites have been found.

Comets

Being in space far from the Sun, comets have the appearance of very faint, blurry, bright spots, in the center of which there is a nucleus. Only those comets that pass relatively close to the Sun become very bright and "tailed". The view of a comet from Earth also depends on the distance to it, the angular distance from the Sun, the light of the Moon, etc. Halley's comet is one of periodic comets... Many short-period comets with orbital periods of three ( comet Encke) up to ten years. Their aphelions lie near the orbit of Jupiter. The comets' approach to the Earth and their future apparent path across the sky are calculated in advance with great accuracy. Along with this, there are comets moving in very elongated orbits with long orbital periods. We take their orbits for parabolas, although in reality they seem to be very elongated ellipses, but it is not easy to distinguish these curves, knowing only a small segment of the path of comets near the Earth and the Sun. Most comets do not have a tail and are visible only through a telescope.

For example, Vesta.

Main characteristics

Terrestrial planets are highly dense and consist mainly of silicates and metallic iron (in contrast to gas planets and rocky-ice dwarf planets, Kuiper belt objects and the Oort cloud). Largest planet the terrestrial group - Earth - is more than 14 times less massive than the least massive gas planet - Uranus, but at the same time about 400 times more massive than the largest known Kuiper belt object.

Terrestrial planets are composed mainly of oxygen, silicon, iron, magnesium, aluminum and other heavy elements.

All terrestrial planets have the following structure:

• In the center there is a core made of iron with an admixture of nickel.
• The mantle is composed of silicates.
• The crust formed as a result of partial melting of the mantle and also consisting of silicate rocks, but enriched in incompatible elements. Of the terrestrial planets, Mercury does not have a crust, which is explained by its destruction as a result of a meteorite bombardment. Earth is different from other terrestrial planets high degree chemical differentiation of matter and widespread distribution of granites in the crust.

Two of the terrestrial planets (the farthest from the Sun - Earth and Mars) have satellites. None of them (unlike all giant planets) have rings.

Terrestrial exoplanets

It is believed that earth-like planets are the most favorable for the emergence of life, therefore, their search attracts close public attention. So in December 2005, scientists from the Institute of Space Sciences (Pasadena, California) reported the discovery of a sun-like star around which rocky planets are supposedly forming. Later, planets were discovered that are only several times more massive than the Earth and, probably, should have a solid surface.

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• Also in antique times the ancient Greeks noticed unusual stars in the night sky, which differed from their sisters in that they moved around the celestial sphere: they accelerated their run, then stopped, or began to move in the other direction, and then returned to their flight again.

• The sky as seen by ancient people

  The sky as seen by ancient people
• Astronomers called them "wanderers", which means "planetos" in Greek.
• Now we all know from school lessons that the planets are celestial bodies that revolve in an orbit around
• At first, people knew only five planets, which they gave the names of the main gods of the ancient pantheon: Mercury, Venus, Mars, Jupiter and Saturn. It is now known that there are eight of them in the solar system, and four of them are terrestrial planets or "earth-like" planets that have a hard surface on which you can walk. This is Mercury, Venus, Earth and Mars.

• The earth rested on three elephants and a giant tortoise

  The earth rested on three elephants and a giant tortoise
• Jupiter, Saturn, Uranus and Neptune are giant planets. Around all the planets, with the exception of Venus and Mercury, at least one satellite revolves. In addition to them, the solar system moves great amount other celestial bodies: asteroids, dwarf planets, meteorites and comets.

• The planets of the solar system

  
  The planets of the solar system
• In this article, we will consider the terrestrial planets and the first of them -
• MERCURY.
• In Roman mythology, Mercury is the fast messenger of the gods, the patron saint of trade and travel.
• 
  
• It is the smallest and closest planet to the Sun, which is three times closer to our star than the Earth, and slightly larger than the Moon in size.
• This planet flies around the Sun in just 88 Earth days, and turns around its axis very slowly: a day on Mercury is equal to 58 Earth days, i.e. lasts almost two months. Having circled the Sun twice, this planet manages to turn around its own axis only three times. On the sunny side, its temperature exceeds 400 degrees, and on the other, where darkness and fierce cold reign - 190 degrees below zero. Mercury has practically no atmosphere.
• This planet is difficult to observe from Earth, because it is always next to the Sun, the bright light of which prevents the small Mercury from being seen. True, sometimes, at sunrise or sunset, while our star is behind the horizon, it can be seen with binoculars or with the naked eye.
• VENUS.
• She got her name in honor of the ancient Roman goddess of love and beauty.

• Venus

  
  Venus
• Since ancient times, it has been called the beautiful Morning and Evening star, tk. This planet reaches its maximum brightness shortly before sunrise or some time after sunset. This is the second planet from our star.
• She is also called the "sister of the Earth", because they are similar in size and gravity. And yet they are completely different.
• A year on Venus lasts 225 Earth days, and a day is longer than a year and is equal to 243 Earth days. It is enveloped in the densest atmosphere of any earth-like planet, which is mainly composed of carbon dioxide. It is impervious to telescopes and highly toxic.
• Under a thick layer of clouds of sulfuric acid, in which terrible hurricanes constantly rage, real hell is hidden: the pressure exceeds the earth's one hundred times, and the temperature on the surface is about 500 degrees of heat.
• EARTH.
• This is the third and largest of the four earth-like planets and, of course, the most dear to us.

• Earth

  
  Earth
• The Earth differs from all planets in that it has air, water and life: seas and oceans, forests and mountains, flowers and trees, animals and birds, and most importantly - we humans. No wonder she was named after the ancient goddess Gaia - the progenitor of all living things.
• In ancient times, the Earth rests on the backs of three whales or elephants, standing on a giant tortoise. Today we all know that our planet has the shape of a flattened ball and with its movements determines the rhythms of our life. Rotating around its axis in 24 hours, it gives us a change of day and night, and bending around the Sun in 365 days in a circle - a change of seasons.
• Traveling around the Sun on our planet, we become one year older with each revolution. Someone else is at the beginning of the path, and someone has flown around it dozens of times.
• French astronomer K. Flammarion said about it this way: "In reality, we are in the sky. The Earth, like a huge ship, took us on board and rushes on a journey around the great star."
• And finally
• MARS,
• which is also included in the terrestrial planets. It is the fourth planet from the Sun and is named after the ancient Roman god of war - Mars.

• Mars

  
  Mars
• And his two companions received the names Phobos and Deimos, which in Greek means "fear" and "horror".
• From Earth, Mars looks like a reddish star, which is why it is called the "red planet".
• The reason is the orange-red tint of the surface, covered with stones, sand and dust, rich in iron oxide (simply rust). The atmosphere here is very rare, and the sky has a pink tint. all because of the same red dust.
• A day on Mars lasts 24 hours 37 minutes, and the changes of the seasons correspond to those of the earth, only last twice as long. The Martian year is equal to 689 Earth days, and the force of gravity is two times weaker than the Earth's. The sun from the "red planet" looks small and dim, and therefore heats it very scarcely: the temperature on the surface on a hot day does not exceed zero degrees, and at night the frozen carbon dioxide settles on the stones from severe frost. It is from it, and not from water, that the Polar Caps mainly consist.
• The famous Martian "canals" that are visible through a telescope are actually traces of destruction of soil, not water currents. On Mars, the most high mountain in the solar system - the extinct volcano Olympus, 26 km high, which is almost three times higher than the earth's Everest. And then there is a gigantic system of canyons up to 11 km deep, called the "Mariner Valley", occupying a quarter of the planet's circumference.
• Hopes of discovering life on Mars have not yet come true, but who knows? Today there are two rovers working there: "Spirit" and "Opportunity", and the flight of a man to the "red planet" is just around the corner.

• Terrestrial planets: Mercury, Venus, Earth and Mars

  Terrestrial planets: Mercury, Venus, Earth and Mars
• When I was in school, I often thought: "Do other stars have planets?"
• There is! They are called exoplanets.
• Today astronomers know for sure about the existence of 763 exoplanets, which are located in 611 planetary systems... And another 2,326 are awaiting scientific confirmation that they actually exist.

• Milky Way Galaxy

  
  Milky Way Galaxy
• In total, only in our Milky Way galaxy there can be 100 billion exoplanets, of which from 5 to 20 billion, possibly similar to our Earth!
• Based on materials by L. Koshman and A. Kirakosyan

The planets are divided into two groups, differing in mass, chemical composition(this is manifested in the differences in their density), rotation speed and the number of satellites.

The four planets closest to the Sun, the terrestrial planets, are small, composed of dense rocky matter and metals. All of them, for example, have a solid surface and, apparently, consist of a substance similar in composition, although the Earth and Mercury are denser than Mars and Venus. Mercury and Venus have no satellites, the Earth has one satellite (the Moon we know), Mars has two satellites - Phobos and Deimos, both very small and clearly different in nature from the Moon.

Far beyond the main asteroid zone are four giant planets: Jupiter, Saturn, Uranus, Neptune. The giant planets are much more massive, consist mainly of light substances and therefore, despite the enormous pressure in their depths, they have a low density. For Jupiter and Saturn, hydrogen and helium account for the bulk of their mass. All giants are accompanied by retinues of satellites: Jupiter has 14 satellites, Saturn has 15, Uranus has 5 and Neptune has 2.

The most distant known planet is Pluto. It cannot be attributed to either of the two groups. In terms of chemical composition, it is close to the group of giant planets, and in size to the terrestrial group.

Comparative table of the main indicators of the terrestrial planets and giant planets:

The solar system has been around for about 5 billion years. This age of the solar system is in agreement with the measurements of the oldest terrestrial and lunar samples.