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The inner region of the solar system is inhabited by various bodies: large planets, their satellites, as well as small bodies - asteroids and comets

The inner region of the solar system is inhabited by various bodies: large planets, their satellites, as well as small bodies - asteroids and cometsSince 2006, a new subgroup has been introduced in the group of planets - dwarf planets, which have the internal qualities of planets (spheroidal shape, geological activity), but are not able to dominate in the vicinity of their orbits due to their low mass. Now the 8 most massive planets - from Mercury to Neptune - were decided to be called simply planets, although astronomers often call them “large planets” in a conversation to distinguish them from dwarf planets. The term "minor planet", which has been used for asteroids for many years, is now recommended not to be used to avoid confusion with dwarf planets

In the area of ​​large planets, we see a clear division into two groups of 4 planets in each: the outer part of this area is occupied by giant planets, and the inside is much less massive planets of the earth group. A group of giants is also usually divided in half: gas giants (Jupiter and Saturn) and ice giants (Uranus and Neptune). In the group of terrestrial planets, a halving is also planned: Venus and the Earth are extremely similar to each other in many physical parameters, and Mercury and Mars are inferior to them in mass by an order of magnitude and are almost devoid of atmosphere (even in Mars it is hundreds of times smaller than the Earth’s, and Mercury is practically absent).

It should be noted that among two hundred satellites of the planets, at least 16 bodies possessing the internal properties of full-fledged planets can be distinguished. Often they exceed their size and masses of dwarf planets, but at the same time they are controlled by gravity of significantly more massive bodies. We are talking about the Moon, Titan, the Galilean satellites of Jupiter and the like. Therefore, it would be natural to introduce into the nomenclature of the solar system a new group for such “subordinate” planetary-type objects, calling them “satellite planets”. But while this idea is under discussion.

Back to the terrestrial planets. Compared to giants, they are attractive in that they have a solid surface on which space probes can land. Since the 1970s, automatic stations and self-propelled vehicles of the USSR and the USA have repeatedly landed and successfully worked on the surface of Venus and Mars. Landing on Mercury has not yet been, because flying in the vicinity of the Sun and landing on a massive atmosphereless body are fraught with great technical problems.

Studying terrestrial planets, astronomers do not forget the Earth itself. The analysis of images from space made it possible to understand a lot in the dynamics of the Earth’s atmosphere, in the structure of its upper layers (where airplanes and even balloons do not rise), in the processes occurring in its magnetosphere. Comparing the structure of the atmospheres of earth-like planets with each other, much can be understood in their history and more accurately predict their future. And since all higher plants and animals live on the surface of our (or not only ours?) Planet, the characteristics of the lower layers of the atmosphere are especially important for us. This lecture is about terrestrial planets; mainly - their appearance and conditions on the surface.

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