Which planets belong to the terrestrial planets? General characteristics of the terrestrial planets

The solar system is the only planetary structure available for direct study. Information derived from research in this area of space is used by scientists to understand the processes taking place in the universe. They provide an opportunity to understand how our system was born and similar to it, what the future holds for all of us.

Classification of the planets of the solar system

Studies of astrophysicists have made it possible to classify the planets of the solar system. They were divided into two types: earth-like and gas giants. The planets of the terrestrial group include Mercury, Venus, Earth, Mars. The gas giants are Jupiter, Saturn, Uranus and Neptune. Pluto from 2006 received the status of a dwarf planet and refers to the objects of the Kuiper belt, differing in their characteristics from the representatives of both groups.

Characteristic of the terrestrial planets

Each type has a set of features related to the internal structure and composition. The high average density and the predominance of silicates and metals at all levels are the main characteristics by which the terrestrial planets differ. Giants in contrast to them have a low density and consist primarily of gases.

All four planets have a similar internal structure: under the hard bark is a viscous mantle enveloping the core. The central structure, in turn, is divided into two levels: a liquid and a solid core. The main constituents of it are nickel and iron. The mantle differs from the core by the predominance of silicon and manganese oxides .

The dimensions of the planets of the solar system, belonging to the terrestrial group, are thus distributed (from the smaller to the larger): Mercury, Mars, Venus, Earth.

The air envelope

Earth-like planets were already surrounded by atmosphere at the first stages of their formation. Initially, carbon dioxide prevailed in its composition . The change in the atmosphere on Earth was facilitated by the appearance of life. Thus, the planets of the terrestrial group are cosmic bodies surrounded by the atmosphere. However, there is one among them, which has lost its air envelope. This is Mercury, the mass of which has not allowed to preserve the primary atmosphere.

Nearest to the Sun

The smallest planet of the terrestrial group is Mercury. His research is hampered by the proximity to the Sun. Since the beginning of the space era, data on Mercury were obtained only from two vehicles: "Mariner 10" and "Messenger." On their basis, it was possible to create a map of the planet and determine some of its features.

Mercury can really be recognized as the smallest planet of the terrestrial group: its radius is a little less than 2,5 thousand kilometers. Its density is close to that of the earth. The ratio of this indicator with the size gives reason to believe that the planet is largely composed of metals.

The movement of Mercury has a number of characteristics. Its orbit is strongly elongated: at the farthest point the distance to the Sun is 1.5 times more than in the nearest one. One revolution around the star the planet does in about 88 terrestrial days. At the same time for such a year, Mercury has time to turn around its axis only one and a half times. This "behavior" is not typical for other planets of the solar system. Presumably, the slowing down of the initially faster movement was caused by the tidal influence of the Sun.

Beautiful and terrible

The planets of the terrestrial group are simultaneously the same and different cosmic bodies. Similar in structure, they all have features that make them impossible to confuse. The nearest to the Sun Mercury is not the hottest planet. On it there are even sections, always covered with ice. Venus, which follows him near the star, is characterized by higher temperatures.

Named in honor of the goddess of love, the planet has long been a candidate for life-friendly space objects. However, the very first flights to Venus disproved this hypothesis. The true essence of the planet is hidden by a dense atmosphere consisting of carbon dioxide and nitrogen. Such an air envelope contributes to the development of the greenhouse effect. As a result, the temperature on the planet's surface reaches +475 ºС. Here, therefore, there can be no life.

The second largest and the remotest from the Sun planet has a number of features. Venus is the brightest point in the night sky after the moon. Its orbit is almost an ideal circle. Around its axis, it moves from east to west. This direction is uncharacteristic for most planets. Turnover around the Sun it makes for 224.7 earth days, and around the axis - for 243, that is, the year here is shorter than the day.

The Third Planet from the Sun

Earth is unique in many ways. It is located in the so-called zone of life, where the sun's rays are not able to turn the surface into a desert, but the heat is enough to keep the planet from getting covered by the ice crust. Slightly less than 80% of the surface is occupied by the World Ocean, forming together with rivers and lakes a hydrosphere, absent on the rest of the planets of the solar system.

The formation of a special atmosphere of the Earth, consisting mainly of nitrogen and oxygen, was promoted by the development of life. As a result of increasing oxygen concentration, the ozone layer formed, which together with the magnetic field protects the planet from the harmful effects of solar radiation.

The only Earth satellite

The moon has a very serious impact on the Earth. Our planet has acquired a natural satellite almost immediately after its formation. The origin of the moon is still a mystery, although there are several plausible hypotheses on this score. The satellite has a stabilizing effect on the slope of the earth's axis, and also causes the planet to decelerate. As a result, each new day becomes slightly longer. Slowdown is the result of the tidal action of the Moon, the same force that causes tides and ebbs in the ocean.

Red Planet

When asked which planets of the terrestrial group are best investigated after ours, there always follows an unambiguous answer: Mars. Due to the peculiarities of location and climate, Venus and Mercury are studied to a much lesser degree.

If you compare the size of the planets of the solar system, then Mars will be on the seventh place in the list. Its diameter is 6800 km, and the mass is 10.7% of the analogous parameter of the Earth.

On the red planet is a very rarefied atmosphere. Its surface is riddled with craters, and here you can see volcanoes, valleys and glacial polar caps. Mars has two satellites. The nearest to the planet - Phobos - is gradually decreasing and in the future will be torn by the gravity of Mars. For Deimos, on the other hand, slow removal is typical.

The idea of the possibility of life on Mars has existed for more than a century. Recent research conducted in 2012, found on the red planet organic substances. It was suggested that the organics could be brought to the surface by a rover from the Earth. However, studies have confirmed the origin of the substance: its source is the red planet itself. Nevertheless, an unambiguous conclusion about the possibility of life on Mars without additional research can not be done.

The planets of the terrestrial group include the objects closest to us in terms of their location. That is why they are better studied today. Astronomers have already discovered several exoplanets, presumably also related to this type. Of course, each such discovery increases the hope of finding life outside the solar system.