The solar system is the only planetary structure available for direct study. The information obtained on the basis of research in this area of space 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 similar to it, what the future holds for all of us.
Classification of the planets of the solar system
Research by astrophysicists has made it possible to classify the planets of the solar system. They were divided into two types: terrestrial and gas giants. The terrestrial planets include Mercury, Venus, Earth, Mars. The gas giants are Jupiter, Saturn, Uranus and Neptune. Pluto has received the status of a dwarf planet since 2006 and belongs to the Kuiper belt objects, which differ in their features from representatives of both named groups.
Characteristics of the terrestrial planets
Each of the types has a set of features related to the internal structure and composition. High average density and dominance of silicates and metals at all levels -these are the main characteristics that distinguish the terrestrial planets. Giants, in contrast, have a low density and are primarily composed of gases.
All four planets have a similar internal structure: under the solid crust is a viscous mantle, enveloping the core. The central structure, in turn, is divided into two levels: liquid and solid core. Its main constituents are nickel and iron. The mantle differs from the core in the predominance of oxides of silicon and manganese.
The sizes of the planets of the solar system belonging to the terrestrial group are distributed in this way (from smallest to largest): Mercury, Mars, Venus, Earth.
Air shell
Earth-like planets were already surrounded by an atmosphere at the first stages of their formation. Initially, carbon dioxide dominated in its composition. The appearance of life contributed to the change in the atmosphere on Earth. The terrestrial planets are, therefore, cosmic bodies surrounded by an atmosphere. However, among them there is one that has lost its air shell. This is Mercury, the mass of which did not allow the preservation of the primary atmosphere.
Closest to the Sun
The smallest terrestrial planet is Mercury. Its study is hampered by its proximity to the Sun. Since the beginning of the space age, data on Mercury have been received only from two vehicles: Mariner-10 and Messenger. Based on them, it was possible to create a mapplanet and determine some of its features.
Mercury can indeed be recognized as the smallest planet of the terrestrial group: its radius is slightly less than 2.5 thousand kilometers. Its density is close to earth. The ratio of this indicator to the size suggests that the planet is largely composed of metals.
The movement of Mercury has a number of features. Its orbit is highly elongated: at the most distant point, the distance to the Sun is 1.5 times greater than at the nearest one. The planet makes one revolution around the star in about 88 Earth days. At the same time, in such a year, Mercury has time to turn around its axis only one and a half times. Such "behavior" is not typical for other planets in the solar system. Presumably the slowdown of the initially faster movement was caused by the tidal influence of the Sun.
Beautiful and terrible
The terrestrial planets include both identical and different space bodies. Similar in structure, they all have features that make them impossible to confuse. Mercury, which is closest to the Sun, is not the hottest planet. It even has areas that are forever covered with ice. Venus, following it closer 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 is hidden by a dense atmosphere consisting of carbon dioxide and nitrogen. Such an air shell contributes to the development of a greenhouseeffect. As a result, the temperature on the surface of the planet reaches +475 ºС. Here, therefore, there can be no life.
The second largest and farthest planet from the Sun has a number of features. Venus is the brightest point in the night sky after the Moon. Its orbit is an almost perfect circle. It moves around its axis from east to west. This direction is not typical for most planets. It completes a revolution around the Sun in 224.7 Earth days, and around the 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 an ice crust. A little less than 80% of the surface is occupied by the World Ocean, which, together with rivers and lakes, forms a hydrosphere that is absent on the rest of the planets of the solar system.
The development of life contributed to the formation of a special atmosphere of the Earth, consisting mainly of nitrogen and oxygen. As a result of the increase in oxygen concentration, the ozone layer was formed, which, together with the magnetic field, protects the planet from the harmful effects of solar radiation.
The only satellite of the Earth
The moon has a fairly serious impact on the Earth. Our planet acquired a natural satellite almost immediatelyafter his education. 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 tilt of the earth's axis, and also causes the planet to slow down. As a result, each new day becomes a little longer. The slowdown is due to the tidal action of the Moon, the same force that causes the ocean to tide and tide.
Red Planet
When asked which terrestrial planets are best explored after ours, there is always an unambiguous answer: Mars. Due to their 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 on the list. Its diameter is 6800 km, and its mass is 10.7% of that of the Earth.
The red planet has a very rarefied atmosphere. Its surface is dotted with craters, you can also see volcanoes, valleys and glacial polar caps. Mars has two satellites. The closest to the planet - Phobos - is gradually decreasing and will be torn apart by the gravity of Mars in the future. Deimos, on the contrary, is characterized by a slow removal.
The idea of the possibility of life on Mars has been around for over a century. The latest research, conducted in 2012, found organic matter on the red planet. It has been suggested that organic matter could have been brought to the surface by a rover from Earth. However, studies have confirmed the origin of the substance: its source isthe red planet itself. Nevertheless, an unambiguous conclusion about the possibility of life on Mars cannot be made without additional research.
The terrestrial planets are the closest space objects to us in terms of location. That is why they are better studied today. Astronomers have already discovered several exoplanets, presumably also of this type. Of course, each such discovery increases the hope of finding life outside the solar system.
