The solar system is the only planetary structure available for direct study. Information obtained on the basis of research in this part of the cosmos is used by scientists to understand the processes taking place in the Universe. They make it possible to understand how our system was born and those similar to it, what the future awaits us all.
Classification of the planets of the solar system
Research by astrophysicists allowed us to classify the planets of the solar system. They were divided into two types: land-like and gas giants. The terrestrial planets include Mercury, Venus, Earth, Mars. The gas giants are Jupiter, Saturn, Uranus and Neptune. Since 2006, Pluto received the status of a dwarf planet and belongs to the objects of the Kuiper belt, which differ in their features from representatives of both of these groups.
Characterization of the terrestrial planets
Each of the types has a set of features related to the internal structure and composition. High average density and the predominance of silicates and metals at all levels - these are the main characteristics that distinguish the planets of the earth group. Giants, by contrast, have a low density and are primarily composed of gases.
All four planets have a similar internal structure: under the hard crust there is a viscous mantle enveloping the core. The central structure, in turn, is divided into two levels: liquid and solid core. Its main components are nickel and iron. The mantle differs from the core in the predominance of silicon and manganese oxides .
The sizes of the planets of the solar system belonging to the earth group are distributed in this way (from the smallest to the largest): Mercury, Mars, Venus, Earth.
Air shell
Earth-like planets were already surrounded by the atmosphere in the early stages of their formation. Initially, its composition was dominated by carbon dioxide. The change in the atmosphere on Earth was promoted by the appearance of life. Thus, the planets of the earth group include cosmic bodies surrounded by the atmosphere. However, there is one among them that has lost its air envelope. This is Mercury, the mass of which did not allow to preserve the primary atmosphere.
Closest to the sun
The smallest planet on earth is Mercury. Its study is complicated by its proximity to the sun. Since the beginning of the space age, data on Mercury has been received only from two devices: Mariner-10 and Messenger. Based on them, it was possible to create a map of the planet and determine some of its features.
Mercury can indeed be recognized as the smallest planet in the earth's group: its radius is a little less than 2.5 thousand kilometers. Its density is close to earth. The ratio of this indicator to size suggests that the planet is largely composed of metals.
The movement of Mercury has a number of features. Its orbit is very elongated: at the most distant point, the distance to the Sun is 1.5 times greater than at the nearest. A planet makes one revolution around a star in about 88 Earth days. Moreover, for such a year, Mercury manages to turn around its axis only one and a half times. Such "behavior" is not characteristic of other planets of the solar system. The deceleration of the initially faster movement was supposedly caused by the tidal influence of the sun.
Beautiful and terrible
The planets of the earth group include the same and different cosmic bodies. Similar in structure, they all have features that make them impossible to confuse. The closest to the Sun Mercury is not the hottest planet. On it there are even areas forever covered with ice. Venus following it in proximity to the star is characterized by higher temperatures.
Named after the goddess of love, the planet has long been a candidate for habitable space objects. However, the very first flights to Venus refuted this hypothesis. The true essence of the planet hides a dense atmosphere, consisting of carbon dioxide and nitrogen. Such an air shell contributes to the development of the greenhouse effect. As a result, the temperature on the planet’s surface reaches +475 º. Here, therefore, there can be no life.
The second largest and remotest planet has a number of features. Venus is the brightest point in the night sky after the moon. Its orbit is an almost perfect circle. Around its axis, it moves from east to west. This direction is uncharacteristic for most planets. It makes a revolution around the Sun in 224.7 Earth days, and around its axis - in 243, that is, a year here is shorter than a day.
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 there is enough heat so that the planet is not covered with ice crust. A little less than 80% of the surface is occupied by the oceans, which together with rivers and lakes form the hydrosphere, which is absent on other planets of the solar system.
The formation of a special atmosphere of the Earth, consisting mainly of nitrogen and oxygen, was facilitated by the development of life. As a result of an increase in oxygen concentration, an ozone layer has formed, which together with a magnetic field protects the planet from the harmful effects of solar radiation.
The only Earth satellite
The moon has a rather serious effect on the Earth. Our planet 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 subject. The satellite has a stabilizing effect on the inclination of the earth's axis, and also causes a slowdown of the planet. As a result, each new day becomes a little longer. Slowdown is a consequence of the tidal action of the moon, the same force that causes the tides in the ocean.
Red Planet
When asked which planets of the earth's group are best studied after ours, there is always a definite answer: Mars. Due to the location and climate, Venus and Mercury have been studied to a much lesser extent.
If we compare the sizes of the planets of the solar system, then Mars will be in seventh place in the list. Its diameter is 6800 km, and its mass is 10.7% of the same parameter of the Earth.
There is a very rarefied atmosphere on the red planet. Its surface is dotted with craters, also here you can see volcanoes, valleys and ice caps. Mars has two satellites. The closest to the planet - Phobos - is gradually decreasing and will be torn in the future by the gravity of Mars. For Deimos, in contrast, a slow removal is characteristic.
The idea of the possibility of life on Mars has been around for more than a century. Recent studies in 2012 found organic matter on the red planet . It has been suggested that Mars rover from the Earth could bring organic matter to the surface. 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 cannot be made without additional research.
The planets of the terrestrial group include the closest to us in their location space objects. Therefore, they are better studied today. Astronomers have already discovered several exoplanets, presumably also of this type. Of course, every such discovery increases the hope of finding life outside the solar system.