Information project
"Terrestrial Planets"
Completed:
11th grade students
Boykova Kristina
Rumyantseva Natalya
MBOU "Maksatikha Secondary School No. 2"
Head: Krasilnikova O.A.
2014-2015 academic year
Terrestrial planets.
Main characteristics.
Mercury.
Venus.
Mars.
Earth.
Formulation of the problem.
Goals and objectives of the project.
Theoretical material. (Presentation)
Conclusion.
Problem
In the 11th grade school course we consider basic issues in astronomy. These questions interested us very much, and we decided to make a project related to this topic. Planet Earth is the only planet on which life has been discovered. We were interested in the terrestrial planets, including Earth, Mars, Venus and Mercury. So what are these planets? Now we will tell you about it!
Project goals and objectives
Develop knowledge about the terrestrial planets.
Introduce students to facts about the terrestrial planets.
Terrestrial planets.
Terrestrial planets - four planets of the solar system: Mercury, Venus, Earth and Mars. They are also calledinner planets , in contrast to the outer planets - giant planets. In structure and composition, some rocky asteroids, for example Vesta, are close to the terrestrial planets.
Main characteristics.
In the center is a core of iron mixed with nickel.
The mantle consists of silicates.
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 meteorite bombardment. The Earth differs from other terrestrial planets in the high degree of chemical differentiation of matter and the wide distribution of granites in the crust.
Two of the terrestrial planets (the farthest from the Sun - Earth and Mars) have satellites. None of them have rings.
Terrestrial planets are highly dense and consist predominantly of silicates and metallic iron. The largest terrestrial planet, Earth, has more than 14 times the mass of the least massive gas planet, Uranus, but is approximately 400 times more massive than the largest known Kuiper Belt object.
Terrestrial planets consist mainly of oxygen, silicon, iron, magnesium, aluminum and other heavy elements.
All terrestrial planets have the following structure:
Mercury.
The mass of the planet is 3.3 10 23 kg. AveragedensityMercury is quite large - 5.43 g/cm³. Acceleration of gravityon Mercury it is 3.70 m/s².Second escape velocity - 4.25km/s Despite its smaller radius, Mercury still exceeds such satellites in massgiant planets like GanymedeAndTitanium. Astronomical symbolMercury is a stylized image of the winged helmet of the god Mercury with hisCaduceusMercury moves around the Sun along a rather elongatedelliptical orbit ( eccentricity 0.205) at an average distance of 57.91 million km (0.387 AU).In its physical characteristics, Mercury resemblesMoon. It has no natural satellites, but has a very rarefied atmosphere. The planet has a large iron core, which is the sourcemagnetic field, the strength of which is 0.01 of the earth's. Mercury's core makes up 83% of the planet's total volume. Temperatures on the surface of Mercury range from 90 to 700TO(from −180 to +430 °C). The solar side heats up much more than the polar regions and the far side of the planet. The surface of Mercury also resembles in many wayslunar - she is strongcratered. The density of craters varies in different areas. The largest crater on Mercury is named after the great Dutch painterRembrandt, its diameter is 716 km. However, the similarity is incomplete - formations are visible on Mercury that are not found on the Moon. An important difference between mountainouslandscapesMercury and the Moon is the presence on Mercury of numerous jagged slopes extending for hundreds of kilometers -scarps. The presence of well-preserved large craters on the surface of Mercurysuggests that over the past 3-4 billion years there was no movement of sections of the crust there on a large scale, and there was also nosurface erosion, the latter almost completely eliminating the possibility of the existence of any significant atmosphere in the history of Mercury.
Venus.
The average distance of Venus from the Sun is 108 millionkm(0,723 ). Distance from Venus tovaries from 40 to 259 million km. Hervery close to circular -is only 0.0068. The period of revolution around the Sun is 224.7 Earth days; average orbital speed -35 km/s. Venus rotates around its axis, tilted 2° from the perpendicular to the orbital plane, from east to west, that is, in the direction opposite to the direction of rotation of most planets. One rotation around its axis takes 243.02 Earth days. Venus is quite close in size to Earth. The planet's radius is 6051.8 km (95% of Earth's), mass - 4.87 10 24 kg (81.5% terrestrial), average density - 5.24 g/cm.The surface layer (bark) is very thin; weakened by high temperature, it weakly prevents the lava from breaking out. Impact craters are a rare element of the Venusian landscape. There are only about 1,000 craters on the entire planet. The atmosphere on Venus was discoveredM. V. Lomonosovduringtransit of Venus across the disk of the SunJune 61761 (new style). The atmosphere of Venus consists mainly of carbon dioxide (96%) and nitrogen (almost 4%). Water vapor and oxygen are contained in it in trace amounts (0.02% and 0.1%). The Venusian atmosphere contains 105 times more gas than Earth's.Pressureat the surface reaches 93 atm, temperature - 750 K (475 °C). This exceeds the surface temperature of Mercury, which is twice as close to the Sun. The reason for such high temperatures on Venus isthe greenhouse effect created by a dense carbon dioxide atmosphere. The density of the atmosphere of Venus at the surface is only 14 times less than the density of water. Despite the slow rotation of the planet, there is no temperature difference between the day and night sides of the planet - the thermal inertia of the atmosphere is so great.
Mars.
Mars has two natural satellites - Phobos And Deimos , which are relatively small and have an irregular shape.The mass of Mars is 10.7% of the mass of the Earth (6.423 10 23 kg versus 5.9736 10 24 kg for the Earth), volume - 0.15 of the Earth's volume, and average linear diameter - 0.53 of the Earth's diameter (6800 km). The topography of Mars has many unique features. Mars has a rotation period andchange of seasonssimilar to Earth's, but its climatemuch colder and drier than on Earth. Temperatures on the planet range from−153 °Cat the pole in winter and up to more+20 °Conequatorat noon. The average temperature is −50 °C. The atmosphere of Mars, consisting mainly ofcarbon dioxide, very rarefied.Pressureat the surface of Mars it is 160 times less than on Earth - 6.1mbarat average surface level. Due to the large difference in altitude on Mars, the pressure at the surface varies greatly. The approximate thickness of the atmosphere is 110 km. Two-thirds of the surface of Mars is occupied by light areas called continents, about a third are 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 -AcidalianAndGreater Sirte. The nature of the dark areas is still a matter of debate. They persist despite the rage on Marsdust storms. At one time, this served as an argument in favor of the assumption that the dark areas were covered with vegetation. Now it is believed that these are simply areas from which, due to their topography, dust is easily blown away. Large-scale images show that the dark areas actually consist of groups of dark streaks and spots associated with craters, hills and other obstacles in the path of 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.
Earth.
Scientific evidence indicates that the Earth was formed from solar nebula about 4.54 billion years ago and soon after that acquired your only one natural satellite - Moon. Presumably life appeared on Earth approximately 3.9 billion years ago, that is, during the first billion after its origin. Since then biosphere The earth has changed significantly atmosphere and others abiotic factors, causing quantitative growth aerobic organisms, as well as the formationozone layer, which together with Earth's magnetic field weakens solar radiation harmful to life, thereby preserving the conditions for the existence of life on Earth. Bark The earth is divided into several segments, or tectonic plates, which move along the surface at speeds of the order of several centimeters per year.It is the largest of the four terrestrial planets in the Solar System, both in size and mass. The Earth's interior is divided into layers according to chemical and physical (rheological) properties, but unlike other terrestrial planets, the Earth has a pronounced externalAndinner core. The outer layer of the Earth is a hard shell consisting mainly of silicates. Frommantleit is separated by a border with a sharp increase in speedslongitudinalseismic waves -Mohorovicic surface. Significant changes in the crystal structure of the mantle occur at a depth of 410-660 km below the surface, encompassing the transition zone that separates the upper and lower mantle. Under the mantle there is a liquid layer consisting of molten iron with impuritiesnickel,sulfurand silicon -Earth's core.On sea levelthe atmosphere exerts on the earth's surface pressure, equal to 1 atm (101.325 kPa). Average density air at the surface - 1.22 g/l. The Earth takes an average of 23 hours 56 minutes and 4.091 seconds (sidereal day) to make one revolution around its axis. Speed rotation planets from west to east is approximately 15 degrees per hour.
Draw a schematic diagram of the location of the planets of 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 giant planets. much more massive than the terrestrial planets. The largest planets of the solar system, Jupiter and Saturn;; the outer ones are smaller, Uranus and Neptune.
The terrestrial planets (Mercury, Venus, Earth, Mars) are similar in size and chemical composition. A characteristic feature of all terrestrial planets is 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 enormous speeds) and internal (tectonic movements and volcanic phenomena) factors. Also, all terrestrial planets except Mercury have an atmosphere. A distinctive feature of the 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's.
Terrestrial planets have some common characteristics. They all have a solid surface and appear to be composed of a substance similar in composition, although Earth and Mercury are more dense than Mars and Venus. Their orbits in general 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 because their orbits lie inside the Earth's; they, like the Moon, come 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, the Earth has one satellite - the Moon, Mars has 2 satellites - Phobos and Deimos, both are very small and differ in nature from the Moon.
MERCURY- the planet closest to the Sun in the Solar System.
As the planet closest to the Sun, Mercury receives significantly more energy from the central star than, for example, the Earth (on average 10 times). The surface of Mercury, covered with crushed basalt-type material, is quite dark. Along with craters (usually 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 hot , a gradually cooling iron-nickel core and silicate shell, at the boundary between which the temperature can approach 103 K. The core accounts for more than half the mass of the planet.
VENUS- the second planet from the Sun and closest 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 areas have been discovered. On the surface of Venus, craters, faults and other signs of intense tectonic processes occurring on it were discovered. Traces of impact bombing are also clearly visible. The surface is covered with stones and slabs of various sizes; surface rocks are similar in composition to terrestrial sedimentary rocks. The predominant proportion 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 consist mainly of 75-80 percent sulfuric acid. Venus's magnetic field is negligible. Due to its relative proximity to the Sun, Venus experiences significant tidal influences, which creates an electric field above its surface, the intensity of which can be twice that of the “fair weather field” observed above the Earth’s surface. Venus has three shells. The first of them - the crust - is approximately 16 km thick. Next is the mantle, a silicate shell that extends to a depth of about 3,300 km to the border with the iron core, the mass of which is about a quarter of the total mass of the planet.
Earth- the third planet from the Sun in the Solar System.
The Earth moves around the Sun. The Earth's surface area is 510.2 million km2, of which approximately 70.8% is in the World Ocean. Land makes up 29.2%, respectively, and forms six continents and islands. The Earth has a single satellite - the Moon. According to modern concepts, the outer core consists of sulfur (12%) and iron (88%). Finally, at depths greater than 5,120 km, seismic methods reveal the presence of a solid inner core, which accounts for 1.7% of the Earth's mass. Presumably it is an iron-nickel alloy (80% Fe, 20% Ni).
The Earth is surrounded by an atmosphere (see Earth's Atmosphere). Its lower layer (troposphere) extends to an average altitude of 14 km; The processes occurring 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, the ozonosphere is of great importance - the 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 the ozone layer, radiation flows would reach the surface of the Earth, causing destruction in living organisms existing there. The Earth also has magnetic and electric fields.
MARS- the fourth planet from the Sun in the Solar System.
Since the inclination of the equator to the orbital plane 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 are reddish-orange in color; 25% of the surface are darker “seas” of gray-green color, the level of which is lower than that of the “continents”. Observations of Mars from satellites reveal clear traces of volcanism and tectonic activity - faults, gorges with branching canyons. The surface of Mars appears 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 thin 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 of the terrestrial planets, although, of course, there are specific differences. The core of Mars is rich in iron and sulfur and is small in size, and its mass is about one tenth of the total mass of the planet. The mantle of Mars is enriched in iron sulfide. The thickness of the lithosphere of Mars is several hundred km, including approximately 100 km of its crust. Two satellites orbit around Mars: Phobos (Fear) and Deimos (Horror). The gravitational fields of satellites are so weak that they do not have an atmosphere. Meteorite craters were discovered on the surface.
The terrestrial planets are the four planets of the solar system: Mercury, Venus, Earth and Mars. They are located in the inner region of the Solar System, in contrast to the giant planets located in the outer region. According to a number of cosmogonic theories, in a significant part of extrasolar planetary systems, exoplanets are also divided into solid planets in the inner regions and gas planets in the outer regions. In structure and composition, some rocky asteroids, for example Vesta, are close to the terrestrial planets.
Main characteristics
Terrestrial planets are highly dense and consist predominantly of silicates and metallic iron (in contrast to gas planets and rock-ice dwarf planets, Kuiper belt objects and the Oort cloud). The largest terrestrial planet, Earth, is more than 14 times less massive than the least massive gas planet, Uranus, but is approximately 400 times more massive than the largest known Kuiper Belt object.
Terrestrial planets consist mainly of oxygen, silicon, iron, magnesium, aluminum and other heavy elements.
All terrestrial planets have the following structure:
- In the center is a core of iron mixed with nickel.
- The mantle consists of silicates.
- 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 meteorite bombardment. The Earth differs from other terrestrial planets in the high degree of chemical differentiation of matter and the wide 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.
– have small sizes and masses, the average density of these planets is several times higher than the density of water; they rotate slowly around their axes; they have few satellites (Mercury and Venus have none at all, Mars has two tiny ones, Earth has one).
The similarity of the terrestrial planets does not exclude significant differences. For example, Venus, unlike other planets, rotates in the direction opposite to its movement around the Sun, and is 243 times slower than the Earth (compare the length of the year and day on Venus). The orbital period of Mercury (i.e., the year of this planet) is only 1/3 greater than the period of its rotation around its axis (relative to the stars). The angles of inclination of the axes to the planes of their orbits for the Earth and Mars are approximately the same, but completely different for Mercury and Venus. Do you know that this is one of the reasons that determines the nature of the change of seasons. Consequently, Mars has the same seasons as the Earth (although each season is almost twice as long as on Earth).
It is possible that, due to a number of physical characteristics, distant Pluto, the smallest of the 9 planets, also belongs to the terrestrial planets. The average diameter of Pluto is about 2260 km. The diameter of Charon, the moon of Pluto, is only half the size. Therefore, it is possible that the Pluto-Charon system, like the Earth-system, is a “double planet”.
Atmospheres
Similarities and differences are also revealed when studying the atmospheres of the terrestrial planets. Unlike Mercury, which, like the Moon, is practically devoid of an atmosphere, Venus and Mars have one. Modern data on the atmospheres of Venus and Mars were obtained as a result of flights of our (“Venera,” “Mars”) and American (“Pioneer-Venera,” “Mariner,” “Viking”) spacecraft. Comparing the atmospheres of Venus and Mars with the Earth's, we see that, unlike the nitrogen-oxygen atmosphere of the Earth, Venus and Mars have atmospheres mainly consisting of carbon dioxide. The pressure at the surface of Venus is more than 90 times greater, and at Mars it is almost 150 times less than at the surface of the Earth.
The temperature at the surface of Venus is very high (about 500°C) and remains almost the same. What is this connected with? At first glance, it seems that Venus is closer to the Sun than the Earth. But, as observations show, the reflectivity of Venus is greater than that of the Earth, and therefore heats both planets approximately equally. The high surface temperature of Venus is due to the greenhouse effect. It is as follows: the atmosphere of Venus transmits the rays of the Sun, which heat the surface. The heated surface becomes a source of infrared radiation, which cannot leave the planet, since it is retained by the carbon dioxide and water vapor contained in the atmosphere of Venus, as well as the cloud cover of the planet. As a result of this, the balance between the influx of energy and its consumption into peaceful space is established at a higher temperature than that which would be on a planet that freely transmits infrared radiation.
We are accustomed to earthly clouds consisting of small drops of water or ice crystals. The composition of Venus's clouds is different: they contain droplets of sulfuric and, possibly, hydrochloric acid. The cloud layer greatly weakens sunlight, but, as measurements performed on the Venera 11 and Venera 12 satellites have shown, the illumination at the surface of Venus is approximately the same as at the surface of the Earth on a cloudy day. Studies carried out in 1982 by the Venera 13 and Venera 14 probes showed that the sky of Venus and its landscape are orange. This is explained by the peculiarity of light scattering in the atmosphere of this planet.
Gas in the atmospheres of the terrestrial planets is in continuous motion. Often during dust storms that last for several months, huge amounts of dust rise into the atmosphere of Mars. Hurricane winds have been recorded in the atmosphere of Venus at altitudes where the cloud layer is located (from 50 to 70 km above the surface of the planet), but near the surface of this planet the wind speed reaches only a few meters per second.
Thus, despite some similarities, in general, the atmospheres of the planets closest to Earth differ sharply from the Earth's atmosphere. This is an example of a discovery that could not have been predicted. Common sense dictated that planets with similar physical characteristics (for example, Earth and Venus are sometimes called “twin planets”) and approximately equally distant from the Sun should have very similar atmospheres. In fact, the reason for the observed difference is related to the peculiarities of the evolution of the atmospheres of each of the terrestrial planets.
The study of atmospheres of the terrestrial group not only allows us to better understand the properties and history of the origin of the earth's atmosphere, but is also important for solving environmental problems. For example, fogs - smogs, formed in the earth's atmosphere as a result of air pollution, are very similar in composition to Venusian clouds. These clouds, like dust storms on Mars, remind us that it is necessary to limit the emission of dust and various types of industrial waste into the atmosphere of our planet if we want to maintain conditions on Earth suitable for the existence and development of life for a long time. Dust storms, during which clouds of dust remain in the atmosphere of Mars for several months and spread over vast areas, make us think about some of the possible environmental consequences of a nuclear war.
Surfaces
Terrestrial planets, like the Earth and the Moon, have rocky surfaces. Ground-based optical observations provide little information about them, since Mercury is difficult to see through a telescope even during elongations, and the surface of Venus is hidden from us by clouds. On Mars, even during great oppositions (when the distance between Earth and Mars is minimal - about 55 million km), occurring once every 15 - 17 years, large telescopes can be used to view details measuring about 300 km. And yet, in recent decades, it has been possible to learn a lot about the surface of Mercury and Mars, as well as to gain insight into the until recently completely mysterious surface of Venus. This became possible thanks to the successful flights of automatic interplanetary stations such as “Venus”, “Mars”, “Viking”, “Mariner”, “Magellan”, which flew near the planets or landed on the surface of Venus and Mars, and thanks to ground-based radar observations.
The surface of Mercury, replete with craters, is very similar to the Moon. There are fewer “seas” there than on the Moon, and they are small. The diameter of the Mercurian Sea of Heat is 1300 km, as is the Sea of Rain on the Moon. Steep ledges stretch for tens and hundreds of kilometers, probably generated by the former tectonic activity of Mercury, when the surface layers of the planet shifted and moved forward. As on the Moon, most craters were formed by meteorite impacts. Where there are few craters, we see relatively young areas of the surface. Old, destroyed craters are noticeably different from younger, well-preserved craters.
The rocky desert and many individual stones are visible in the first photo-television panoramas transmitted from the surface of Venus by the automatic stations of the “Venus” series. Radar ground observations have discovered many shallow craters on this planet, with diameters ranging from 30 to 700 km. In general, this planet turned out to be the smoothest of all the terrestrial planets, although it also has large mountain ranges and long hills, twice the size of terrestrial Tibet. The extinct volcano Maxwell is enormous, its height is 12 km (one and a half times greater than Chomolungma), the diameter of the base is 1000 km, the diameter of the crater at the top is 100 km. The Gauss and Hertz volcanic cones are very large, but smaller than Maxwell. Like rift gorges stretching along the bottom of the Earth’s oceans, rift zones have also been discovered on Venus, indicating that active processes (for example, volcanic activity) once occurred on this planet (and perhaps are still occurring now!).
In 1983 – 1984 Radar studies were carried out from the stations “Venera - 15” and “Venera - 16”, which made it possible to create a map and atlas of the planet’s surface (the size of the surface details is 1 – 2 km). A new step in the study of the surface of Venus is associated with the use of a more advanced radar system installed on board the American satellite Magellan. This spacecraft reached the vicinity of Venus in August 1990 and entered an elongated elliptical orbit. Regular surveys have been carried out since September 1990. Clear images are transmitted to Earth, some of them clearly show details up to 120 m in size. By May 1993, almost 98% of the planet's surface was surveyed. It is planned to complete the experiment, which includes not only photographing Venus, but also conducting other studies (gravitational field, atmosphere, etc.) in 1995.
The surface of Mars is also replete with craters. There are especially many of them in the southern hemisphere of the planet. The dark areas that occupy a significant part of the planet's surface are called seas (Hellas, Argir, etc.). The diameters of some seas exceed 2000 km. Hills resembling the earth's continents, which are light fields of orange-red color, are called continents (Tharsis, Elysium). 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 base diameter 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 surface layers shifted is evidenced by the remains of lava flows, huge surface faults (one of them, Mariner, stretches for 4000 km), numerous gorges and canyons. It is possible that it was some of these formations (for example, chains of craters or extended gorges) that Mars researchers 100 years ago mistook for “channels,” the existence of which they subsequently tried to explain for a long time by the activities of intelligent inhabitants of Mars.
The red color of Mars has also ceased to be a mystery. It is explained by the fact that the soil of this planet contains a lot of clays rich in iron.
Panoramas of the surface of the “Red Planet” were repeatedly photographed and transmitted from close range.
You know that almost 2/3 of the Earth's surface is occupied by oceans. There is no water on the surface of Venus and Mercury. There are no open bodies of water on the surface of Mars either. But, as scientists suggest, water on Mars should be at least in the form of a layer of ice that forms the polar caps, or as an extensive layer of permafrost. You may witness the discovery of ice reserves on Mars, or even water underneath the ice. The fact that there was once water on the surface of Mars is evidenced by the dried, channel-like winding depressions discovered there.
Planets related to terrestrial group - Mercury, Venus, Earth, Mars, Pluto- have small sizes and masses, the average density of these planets several times higher than the density of water; they rotate slowly around their axes; they have few satellites (Mercury and Venus have none at all, Mars has two, Earth- one).
Similarities planets terrestrial groups does not exclude some differences. For example, Venus, unlike others planets, rotates in the direction opposite to its movement around Sun, and 243 times slower than the Earth.. The orbital period of Mercury (i.e., the year of this planets) is only 1/3 greater than the period of its rotation around its axis.
The angles of inclination of the axes to the planes of their orbits for the Earth and Mars are approximately the same, but completely different for Mercury and Venus. Consequently, Mars has the same seasons as the Earth, although they are almost twice as long as on Earth.
Possibly to planets terrestrial groups attribute and distant Pluto- the smallest of 9 planets. The average diameter of Pluto is about 2260 km. The diameter of Charon, the moon of Pluto, is only half the size. Therefore, it is possible that the Pluto-Charon system, like the Earth-Moon system, represents "double planet«.
Similarities and differences are also found in atmospheres planets terrestrial groups. Unlike Mercury, which, like the Moon, is practically devoid of an atmosphere, Venus and Mars have one. Venus has a very dense atmosphere, mainly consisting 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 at Mars almost 150 times less than at 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. The thick, dense atmosphere allows the rays of the Sun to pass through, but blocks infrared thermal radiation coming from the heated surface. Gas in atmospheres planets terrestrial groups is in continuous motion. Often during dust storms that last for several months, huge amounts of dust rise into the atmosphere of Mars. Hurricane winds have been 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 speed reaches only a few meters per second.
Planets terrestrial groups, like the Earth and the Moon, have hard surfaces tee. The surface of Mercury, replete with craters, is very similar to the Moon. There are fewer “seas” there than on the Moon, and they are small. As on the Moon, most craters were formed by meteorite impacts. Where there are few craters, we see relatively young areas of the surface.
The rocky desert and many individual stones are visible in the first photo-television panoramas transmitted from the surface of Venus by automatic stations of the Venus series. Radar ground observations discovered on this planet many shallow craters, the diameters of which range from 30 to 700 km. Overall this planet turned out to be the smoothest of all planets terrestrial groups, although it also has large mountain ranges and extensive hills, twice the size 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.
The surface of Mars is replete with craters. There are especially many of them in the southern hemisphere planets. Dark areas that occupy a significant portion of the surface planets, received the name of the seas. The diameters of some seas exceed 2000 km. Hills resembling the earth's 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 base diameter 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 surface layers shifted is evidenced by the remains of lava flows, huge surface faults (one of them, Mariner, stretches for 4000 km), numerous gorges and canyons.