What planets are part of the terrestrial group. Abstract: Terrestrial planets
Pluto - all of them have small masses and sizes, their average density is several times higher than the density of water; they are able to slowly rotate around their personal axes; they have a small number of satellites (Mars has two, the Earth has only one, and Venus and Mercury have none at all).
The similarity of the planets in the terrestrial group does not exclude some differences. For example, Venus rotates in the opposite direction from the movement around the Sun, and two hundred and forty-three times slower than the Earth. The period of rotation of Mercury (that is, the year of this planet) is only one third more than the period of its rotation around its axis.
The angle of inclination of the axis to the planes of the orbits of Mars and the Earth is approximately the same, but quite different for Venus and Mercury. Just like the Earth, there are seasons, which means that on Mars, although almost 2 times longer than on Earth.
It is possible that distant Pluto, the smallest of the nine planets, can also be attributed to the terrestrial planets. The usual diameter of Pluto was more than two thousand kilometers. Only 2 times smaller than the diameter of Pluto's satellite - Charon. Therefore, it is not a fact that the Pluto-Charon system, like the Earth-system, is a double planet.
Similarities and differences are also found in the atmospheres of the terrestrial planets. Venus and Mars have an atmosphere, unlike Mercury, which, however, like the Moon, is practically devoid of it. Venus has a fairly dense atmosphere, mostly composed of sulfur compounds and carbon dioxide. The atmosphere of Mars, on the contrary, is too rarefied and very poor in nitrogen and oxygen. The pressure at the surfaces of Venus is almost a hundred times more, while at Mars it is almost a hundred and fifty times less than at the surfaces of the Earth.
The fever near the surfaces of Venus is quite high (about five hundred degrees Celsius) and remains almost the same all the time. Heat surfaces of Venus is determined by the greenhouse effect. The dense atmosphere releases the rays of the Sun, but delays the thermal infrared radiation that comes from heated surfaces. The gas in the atmosphere of a terrestrial planet is in constant motion. Often, during a dust storm that lasts more than one month, a large amount of dust rises into the atmosphere of Mars.
Draw a schematic diagram of the position of the planets in the solar system relative to the sun.
The four smaller inner planets: Mercury, Venus, Earth and Mars are terrestrial planets
The four outer planets, Jupiter, Saturn, Uranus and Neptune, are the giant planets. much more massive than the terrestrial planets. The largest planets in the solar system, Jupiter and Saturn;;; outer - smaller, Uranus and Neptune.
The terrestrial planets (Mercury, Venus, Earth, Mars) are similar in size and chemical composition. Characteristic all terrestrial planets - the presence of a solid lithosphere. The relief of their surface was formed as a result of the action of external (impacts of bodies falling on planets at great speeds) and internal (tectonic movements and volcanic phenomena) factors. Also, all terrestrial planets except Mercury have an atmosphere. Distinctive feature Earth from other terrestrial planets is the presence of an atmosphere.
The atmospheres of Mars and Venus are very similar in composition to each other, but at the same time they differ significantly from the earth.
The terrestrial planets have some General characteristics. All of them have a solid surface, apparently, consist of a substance similar in composition, although the Earth and Mercury are denser than Mars and Venus. Their orbits generally do not differ from circular ones, only the orbits of Mercury and Mars are more elongated than those of the Earth and Venus.
Mercury and Venus are called inner planets, since their orbits lie inside the earth; they, like the Moon, are in different phases - from new to full - and remain in the same part of the sky as the Sun. Mercury and Venus have no satellites, Earth has one satellite - moon, Mars has 2 satellites - Phobos and Deimos, both are very small and differ in nature from the Moon.
MERCURY is the closest planet to the Sun in the solar system.
As the planet closest to the Sun, Mercury receives much more energy from the central luminary than, for example, the Earth (10 times on average. The surface of Mercury, covered with crushed basalt-type matter, is rather dark. Along with craters (as a rule, less deep than on the Moon) there are hills and valleys. Above the surface of Mercury there are traces of a very rarefied atmosphere containing, in addition to helium, also hydrogen, carbon dioxide, carbon, oxygen and noble gases (argon, neon. Mercury also has a magnetic field. The planet consists of a hot, gradually cooling iron-nickel core and a silicate shell, at the border between which the temperature can approach 103 K. The core accounts for more than half of the mass planets.
VENUS It is the second planet from the Sun and the closest planet to Earth in the solar system.
Venus is the only planet in the solar system whose own rotation is opposite to the direction of its revolution around the sun. The surface of Venus is predominantly (90%) flat, although three elevated regions have been found. On the surface of Venus, craters, faults, and other signs of intense tectonic processes were found. Traces of shock bombardment are also clearly visible. The surface is covered with stones and slabs of various sizes; surface rocks are close in composition to terrestrial sedimentary rocks. The predominant share of the atmosphere is carbon dioxide (~ 97%); nitrogen - about 3%; water vapor - less than a tenth of a percent, oxygen - thousandths of a percent. The clouds of Venus are mostly composed of 75-80% sulfuric acid. The magnetic field of Venus is negligible. Due to its relative proximity to the Sun, Venus experiences significant tidal influences, due to which an electric field arises above its surface, the strength of which can be twice the strength of the "clear weather field" observed above the Earth's surface. There are three shells on Venus. The first of them - the crust - has a thickness of about 16 km. Next is the mantle, a silicate shell extending to a depth of about 3300 km to the border with the iron core, the mass of which is about a quarter of the entire mass of the planet.
Earth is the third planet from the sun in the solar system.
The Earth moves around the Sun. The surface area of the Earth is 510.2 million km2, of which approximately 70.8% is in the oceans. Land makes up 29.2%, respectively, and forms six continents and islands. The Earth has a single satellite, the Moon. By modern ideas the outer core is composed of sulfur (12%) and iron (88%). Finally, at depths greater than 5120 km, seismic methods reveal the presence of a solid inner core, which accounts for 1.7% of the Earth's mass. Presumably, this is an iron-nickel alloy (80% Fe, 20% Ni).
The earth is surrounded by an atmosphere (see Atmosphere of the Earth). Its lower layer (troposphere) extends on average to a height of 14 km; the processes taking place here play a decisive role in the formation of weather on the planet. Even higher (up to about 80-85 km) is the mesosphere, above which noctilucent clouds are observed (usually at an altitude of about 85 km). For biological processes on Earth great value has an ozonosphere - an ozone layer located at an altitude of 12 to 50 km. The area above 50-80 km is called the ionosphere .. If it were not for ozone layer, radiation fluxes would reach the surface of the Earth, causing destruction in the living organisms existing there. The Earth also has magnetic and electric fields.
MARS is the fourth planet from the sun in the solar system.
Since the inclination of the equator to the plane of the orbit is significant (25.2 °), there are noticeable seasonal changes on the planet. A significant part of the surface of Mars is lighter areas (“continents”) that have a reddish-orange color; 25% of the surface are darker "seas" of a gray-green color, the level of which is lower than that of the "continents". Observations of Mars from satellites reveal distinct traces of volcanism and tectonic activity - faults, gorges with branching canyons. The surface of Mars seems to be a waterless and lifeless desert, over which storms rage, raising sand and dust to a height of tens of kilometers. The atmosphere on Mars is rarefied and consists mainly of carbon dioxide (about 95%) and small additions of nitrogen (about 3%), argon (about 1.5%) and oxygen (0.15%). The chemical composition of Mars is typical for the planets of the Earth group, although, of course, there are specific differences. The core of Mars is rich in iron and sulfur and is small in size and weight about one tenth of the total mass of the planet. The mantle of Mars is enriched with iron sulfide. The thickness of the lithosphere of Mars is several hundred km, including about 100 km of its crust. Two satellites circulate around Mars: Phobos (Fear) and Deimos (Horror). The gravitational fields of satellites are so weak that they have no atmosphere. Meteor craters have been found on the surface.
planets related to terrestrial group - Mercury, Venus, Earth, Mars, Pluto- have small sizes and masses, the average density of these planets several times greater than the density of water; they slowly rotate around their axes; they have few satellites (Mercury and Venus have none at all, Mars has two, Earth- one).
similarity planets terrestrial groups does not rule out some difference.. For example, Venus, unlike other planets, rotates in the opposite direction to its movement around sun, and 243 times slower than the Earth .. Mercury's orbital period (i.e., the year of this planets) is only 1/3 more than the period of its rotation around the axis.
The angles of inclination of the axes to the planes of their orbits for the Earth and Mars are approximately the same, but quite different for Mercury and Venus. The same as the Earth, the seasons are, therefore, on Mars, although almost twice as long as on Earth.
Possibly to planets terrestrial groups attributed and distant Pluto- the smallest of 9 planets. The average diameter of Pluto is about 2260 km. Only half the diameter of Pluto's moon Charon. Therefore, it is possible that the Pluto-Charon system, like the Earth-Moon system, is "double planet«.
Similarities and differences are also found in the atmospheres planets terrestrial groups. Unlike Mercury, which, like the Moon, is practically devoid of an atmosphere, Venus and Mars have it. Venus has a very dense atmosphere, mainly composed of carbon dioxide and sulfur compounds. The atmosphere of Mars, on the contrary, is extremely rarefied and also poor in oxygen and nitrogen. The pressure at the surface of Venus is almost 100 times greater, and that of Mars is almost 150 times less than that of the surface of the Earth.
The temperature at the surface of Venus is very high (about 500 ° C) and remains almost the same all the time. The high surface temperature of Venus is due to the greenhouse effect. A dense dense atmosphere transmits the rays of the Sun, but delays infrared thermal radiation coming from a heated surface .. Gas in atmospheres planets terrestrial groups is in constant motion. Often, during dust storms that last for several months, a huge amount of dust rises into the atmosphere of Mars. Hurricane winds were recorded in the atmosphere of Venus at altitudes where the cloud layer is located (from 50 to 70 km above the surface planets), but near the surface of this planets Wind speeds are only a few meters per second.
planets terrestrial groups, like the Earth and the Moon, have hard surfaces ty. The surface of Mercury, replete with craters, is very similar to the moon. There are fewer “seas” than on the Moon, and they are small. As on the Moon, most of the craters were formed as a result of meteorite impacts. Where there are few craters, we see relatively young areas of the surface.
The stony desert and many individual stones are visible on the first photo-television panoramas transmitted from the surface of Venus by automatic stations of the Venera series. Radar ground observations were found on this planet many shallow craters with diameters from 30 to 700 km. In general, this planet turned out to be the smoothest planets terrestrial groups, although it also has large mountain ranges and extended hills, twice the size of terrestrial Tibet.
Almost 2/3 of the Earth's surface is occupied by oceans, but there is no water on the surface of Venus and Mercury.
Replete with craters and the surface of Mars. Especially a lot of them in the southern hemisphere planets. Dark areas occupying a significant part of the surface planets, are called the seas. The diameters of some seas exceed 2000 km. Hills, reminiscent of terrestrial continents, which are light fields of orange-red color, are called continents. Like Venus, there are huge volcanic cones. The height of the largest of them - Olympus - exceeds 25 km, the diameter of the crater is 90 km. The diameter of the base of this giant cone-shaped mountain is more than 500 km. The fact that millions of years ago powerful volcanic eruptions occurred on Mars and the surface layers shifted is evidenced by the remnants of lava flows, huge surface fractures (one of them - Mariner - stretches for 4000 km), numerous gorges and canyons.
Chapter 8. Planets of the terrestrial group: Mercury, Venus, Earth
planet formation
One way or another, but at the moment 8 planets are known in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and several plutonoids, including Pluto, which until recently was listed among the planets. All planets orbit in the same direction and in the same plane and almost in circular orbits (with the exception of the plutonoids). From the center to the outskirts of the solar system (to Pluto) 5.5 light hours. The distance from the Sun to the Earth is 149 million km, which is 107 of its diameters. The first planets from the Sun are strikingly different in size from the latter and, unlike them, are called terrestrial planets, and the distant planets are called giant planets.
Mercury
Mercury, the closest planet to the sun, is named after the Roman god of commerce, travelers and thieves. This small planet orbits quickly and rotates very slowly around its axis. Mercury has been known since ancient times, but astronomers did not immediately understand that it was a planet, and that in the morning and in the evening they see the same star.
Mercury is located at a distance of about 0.387 AU from the Sun. (1 AU is equal to the average radius of the Earth's orbit), and the distance from Mercury to the Earth, as it and the Earth move along their orbits, varies from 82 to 217 million km. The inclination of the plane of Mercury's orbit to the plane of the ecliptic (the plane solar system) is 7°. The axis of Mercury is almost perpendicular to the plane of its orbit, and its orbit is elongated. Thus, on Mercury there is no change of seasons, and the change of day and night occurs very rarely, about once every two Mercury years. One side of it, facing the Sun for a long time, is very hot, and the other, turned away from the Sun for a long time, is in terrible cold. Mercury moves around the Sun at a speed of 47.9 km/s. The weight of Mercury is almost 20 times less than the weight of the Earth (0.055M), and the density is almost the same as that of the Earth (5.43 g/cm3). The radius of the planet Mercury is 0.38R (radius of the Earth, 2440 km).
Due to the proximity to the Sun, under the influence of gravity, powerful tidal forces arose in the body of Mercury, which slowed down its rotation around its axis. In the end, Mercury found itself in a resonant trap. The period of its revolution around the Sun, measured in 1965, was 87.95 Earth days, and the period of rotation around its axis was 58.65 Earth days. Mercury completes three complete revolutions around its axis in 176 days. During the same period, the planet makes two revolutions around the Sun. In the future, the tidal deceleration of Mercury should lead to the equality of its revolution around its axis and the revolution around the Sun. Then it will always be turned to the Sun with one side, like the Moon to the Earth.
Mercury has no satellites. Perhaps, once upon a time, Mercury itself was a satellite of Venus, but due to solar gravity, it was "taken away" from Venus and became an independent planet. The planet is actually spherical. Acceleration free fall on its surface is almost 3 times less than the earth's (g = 3.72 m/s 2 ).
The proximity to the Sun makes it difficult to observe Mercury. In the sky, it does not move far from the Sun - a maximum of 29 °, from the Earth it is visible either before sunrise ( morning visibility), or after sunset (evening visibility).
In terms of its physical characteristics, Mercury resembles the Moon; there are many craters on its surface. Mercury has a very thin atmosphere. The planet has a large iron core, which is the source of gravity and magnetic field, the strength of which is 0.1 of the strength of the Earth's magnetic field. Mercury's core makes up 70% of the planet's volume. Surface temperatures range from 90° to 700° K (-180° to +430° C). The sunlit equatorial side is heating up much more than the polar regions. different degree surface heating creates a difference in the temperature of the rarefied atmosphere, which should cause its movement - the wind.
By their own physical properties planets can be divided into two categories: giant planets and terrestrial planets.
Which planets are terrestrial planets
To the category of planets of the terrestrial group, scientists attributed Mercury, Mars, Venus and the Earth. All of them have a rather modest size and weight. The density of the planets under consideration is many times higher than the density of water. The speed of rotation around its own axis is quite small, as well as a small number of satellites (Venus and Mercury do not have them at all, but the Earth boasts one satellite - the moon).
However, if these planets have similar features, this does not mean at all that there are no differences. For example, the rotation of Venus occurs in the opposite direction to its rotation around the Sun, and the rotation speed is more than 240 times less than that of the Earth (this is evidenced by the number of days in a year on Venus). The duration of the year on Mercury (that is, around the sun) is only a third longer than the duration of its revolution around its own axis. The axes to the planes of the Earth and Martian orbits are inclined at approximately the same angle, but the inclination of the axes of Venus and Mercury are very different. And this, in turn, is one of the most important reasons why the change of seasons is determined. The Earth has its own seasons of the year, identical ones are observed on Mars (although each season lasts twice as long as that of the Earth).
There is a possibility that, according to physical properties, both small and distant Pluto can be attributed to the category of planets of the category under consideration. In diameter, Pluto exceeds 1200 kilometers, which is only half the diameter of its own satellite, Charon. It is possible that Pluto and Charon, like the Earth with the Moon, is a "double planet".
Characteristics of the terrestrial planets
The atmospheric properties of planets in this category have both common features and distinctive features. For example, Mars and Venus have their own atmosphere, while Mercury, like the Moon, is almost deprived of the atmosphere. The density of the atmosphere on Venus is quite high, because it contains mainly carbon dioxide and sulfur compounds. And the Martian atmosphere is not rich in oxygen and nitrogen, as a result of which it is very rarefied. The surface pressure of Venus is almost a hundred times higher than the pressure of the earth's surface, and Mars in this parameter lags behind the Earth by 150 times.
The temperature on Venus almost never changes and stays for quite a high level– about 500°С. This hot climate is due to the greenhouse effect. The atmosphere, which has a high density, although it passes the sun's rays through itself, does not give way to infrared thermal radiation emanating from a hot surface. The gas masses contained in the atmosphere of the terrestrial planets are constantly moving. Often, during periods of dust storms that last more than one month, a colossal volume of dust masses rises into the Martian atmosphere. And during storm winds on Venus, occurring at the level of the cloud layer (about 50-70 km from Venus), closer to the planet, the wind speed is a few meters per second.
The surface of the planets of the terrestrial group, as well as the earth's surface, as well as the surface of its satellite, is solid. Mercury is similar to the Moon in that it is rich in many craters. The so-called "seas" here are quite small, and their number, compared to the same Moon, is much smaller. Most of Craters appeared due to falling on the surface of meteorites. Thanks to this, younger surface areas can be distinguished - the more craters, the older the area.
The surface of Venus is characterized by its numerous stones and rocky desert, which can be observed on the first photo panoramas sent from the surface of this planet by automated stations of the Venus series. The study of the surface of Venus revealed numerous small craters with a diameter ranging from 30-700 km. The surface of Venus is more even than that of other terrestrial planets, although it boasts large mountain ranges and long hills that are twice the size of our Tibet.
Approximately two-thirds of the earth's surface is covered by oceans, while Mercury or Venus have no water at all.
Mars is also rich in craters. Most of them are grouped in its southern hemisphere. Quite pronounced dark areas covering a decent part of the planet are called seas. Some seas are over 2,000 km in diameter. Light areas of orange and red colors, representing hills, which are similar to the continents of the Earth, received the names of the continents. Here you can see large cones of volcanoes, as well as on the surface of Venus. The largest of them is Olympus. It rises more than 25 km, the diameter of the crater is 90 km, and the diameter of the base of this giant is over 500 km. The remnants of lava flows, many canyons and gorges indicate that about millions of years ago, strong volcanic eruptions occurred on the Martian surface, and surface plates moved.
What are the similarities of the terrestrial planets
The structure of planets of this type is approximately identical: in the center is a core of metal, which is formed by and large from iron, around a silicate shell. Planets of this type have similar surface features: craters, elevations, canyons, mountain ranges, etc. Their presence is due to two factors: whether there is water and what kind of tectonic activity.
Planets in this category have secondary atmospheres that have appeared due to fallen comets or due to the activity of volcanoes. These planets have either few or no moons. Mercury and Venus do not have satellites, the Earth can boast of the only satellite - the Moon, but Mars has two of them at once - Phobos and Deimos, which in themselves resemble more asteroids, rather than planetary satellites.
How are the terrestrial planets different?
- It is common for planets of this category to rotate around the axis in their own way: While one earthly revolution is 24 hours, then for Venus it can last up to 243 days.
- Venus is the only one of the four planets that rotates inversely to its movement around the Sun.
- Mars and Earth have almost identical axial tilt angles to the plane of their orbits, while these angles are completely different for Venus and Mercury.
- These planets' atmospheres range from dense atmospheres of carbon dioxide on Venus to almost none on Mercury.
- Mercury and Venus are deprived of the presence of water, and the earth's surface is two-thirds of the water surface.
- Venus lacks the iron core typical of other planets.
Atmosphere of the terrestrial planets
planetary atmospheres earth type appeared immediately after their creation. It included in its composition, for the most part, carbon dioxide formed at the time of layer-by-layer separation immediately after the accretion stage. The chemical composition of the earth's atmosphere was seriously affected by the appearance of life on it: the amount of carbon dioxide decreased, and the proportion of oxygen increased. Mercury and the Moon did not have enough mass to hold an atmosphere. The atmospheres of Mars and Venus contain more carbon dioxide than Earth.
Satellites of the terrestrial planets
Mercury and Venus do not have natural satellites. Therefore, we will get acquainted only with the terrestrial and Martian satellites.
Earth satellite - Moon
Our planet is rich in one single satellite - the Moon. It was studied in such detail as no other cosmic body has been studied. In addition, only a person managed to visit here.
Although everyone knows that the Moon is a satellite, theoretically it could become a full-fledged planet if its orbit passed around the Sun. The lunar diameter is almost 3.5 thousand kilometers, which exceeds even the size of Pluto.
The Moon is a full member of the Earth-Moon gravity system. The moon's mass is not very large, but they have a common center of mass with the Earth.
Among all cosmic bodies, in addition to the Sun, the Moon has the greatest influence on the Earth. A prime example This is the lunar ebb and flow, changing the water level in the oceans.
The entire lunar surface is strewn with craters. This is due to the fact that the Moon does not have its own atmosphere capable of defending its surface from meteorites. In addition, the earth satellite does not have water and wind, with the help of which the places where meteorites would fall would be leveled. During the entire existence of the Moon, that is, for four billion years, the lunar surface has collected huge amount craters.
Martian satellites
Mars has two small satellites - Phobos and Deimos - discovered in 1877 by A. Hall. It is interesting that at some point he was already so desperate to find the satellites of Mars that he almost completed the study, but his wife persuaded him. And the next day, Hall found Deimos. Another six days later - Phobos. On the surface of the second, he discovered a giant crater ten kilometers wide (which is about half the width of Phobos). The researcher gave him the name of his wife's maiden name - Stickney.
Both the one and the other satellite are shaped like an ellipsoid. Due to their small size, gravity is not enough to squeeze the satellites into a rounded shape.
It is curious that Mars has an effect on Phobos, gradually reducing the speed of its movement. Because of this, the orbit of the satellite is shifting closer and closer to the planet. Eventually Phobos will fall to Mars. For a hundred years, this satellite approaches the surface of the planet by nine centimeters. Therefore, about eleven million years will pass before the moment of their collision. But Deimos, in turn, is systematically moving away from the planet and over time will be covered by solar forces. That is, at some point in its existence, Mars will be left without both satellites.
Martian satellites are always located on the same side to the planet, because the time of revolution around its own axis coincides with the time of rotation around Mars. In this property they are like the moon, reverse side which, too, can never be seen from the earth's surface.
Phobos and Deimos are very small in size. Even the lunar diameter exceeds Phobos by 158 times, and Deimos by 290.
Researchers argue about the origin of the satellites of Mars to this day. It could be asteroids that fell into the gravity field of Mars. However, their structure distinguishes them from asteroids, which testifies against such a theory. Another version - two satellites formed due to the split of the once only Martian satellite into two parts.
Characteristics of the surface of the terrestrial planets
The surface of the planets under consideration was formed under the influence of the primary activity of volcanoes. At first, when the planets were quite hot, volcanic activity was very active. And later, the surface of the planets changed due to the activity tectonic plates, volcanic eruptions and meteorites falling on it.
The surface of Mercury resembles that of the moon. Only one thing is different - the presence of infrequent almost perfectly flat areas that are older than the same lunar areas, because they appeared during the fall of meteorites.
The Martian surface has a red hue due to a considerable amount of iron oxide impurities. Craters cover mostly only the southern Martian hemisphere. Scientists have not yet identified the exact reason for this: perhaps an unknown cataclysm was to blame, or maybe the waters of the ocean were simply in this part.
It is known that rivers flowed on the Martian surface in the past, as evidenced by the remaining dried-up channels. In addition to rivers, Mars is interesting for volcanoes, the size of some of them is amazing.
Chemical composition and density of the terrestrial planets
Planets similar to Jupiter are usually gas giants containing helium and hydrogen, because there is more of this gas. No matter how you add these substances, you still end up with a planet, which, by and large, consists of gas.
The stone planets of the terrestrial group formed closer to the Sun. The closer to the star, the easier the gases from these planets were blown away. So education chemical composition planets of the terrestrial group proceeded with the interaction of solid particles. The formation began, initially, with dust, which contains a very small amount of hydrogen, and almost no helium at all. Therefore, the stone planets of the terrestrial group are formed from the universal system of elements.
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