The description of the solar system contains not only information about the eight planets and Pluto, but also several other structures, including a large number of cosmic bodies. These include the Kuiper belt, the scattered disk, the Oort cloud, and the asteroid belt. The latter will be discussed below.
Definition
The term "asteroid" was borrowed by William Herschel from the composer Charles Burney. The word is of Greek origin and means "like a star". The use of such a term was due to the fact that when studying the expanses of space through a telescope, asteroids seemed like stars: they looked like dots, unlike planets, which resembled disks.
As such, there is no definition of the term today. The main characteristic feature of the objects of the asteroid belt and similar structures is the size. The lower limit is a diameter of 50 m. Smaller cosmic bodies are already meteors. The upper limit is the diameter of the dwarf planet Ceres, almost 1000 km.
Location and some features
The asteroid belt lies between the orbits of Mars and Jupiter. Today, more than 600 thousand of its objects are known, of which over 400,000 have their own number or even a name. Approximately 98% of the latter are asteroid belt objects, distant from the Sun at a distance of 2.2 to 3.6 astronomical units. The largest body among them is Ceres. At the IAU meeting in 2006, she, along with Pluto and several other objects, received the status of a dwarf planet. Next in size, Vesta, Pallas and Hygiea, together with Ceres, account for 51% of the total mass of the asteroid belt.
Shape
Space bodies that make up the belt, in addition to size, have a number of basic characteristics. All of them are rocky objects that revolve in their orbits around the Sun. Observations of asteroids made it possible to establish that, as a rule, they have an irregular shape and rotate. Pictures taken by spacecraft flying through the asteroid belt in the solar system confirmed these assumptions. According to scientists, this shape is the result of frequent collisions of asteroids with each other and other objects.
Composition
Today, astronomers distinguish three classes of asteroids according to the main substance that makes up their composition:
- carbon (class C);
- silicate (class S) with a predominance of silicon;
- metal (class M).
The former make up approximately 75% of all known asteroids. Such a classification, however,is not considered acceptable by some scholars. In their opinion, the existing data do not allow us to unequivocally state which element prevails in the composition of the cosmic bodies of the asteroid belt.
In 2010, a group of astronomers made an interesting discovery regarding the composition of asteroids. Scientists have discovered on the surface of Themis, a rather large object of this zone, water ice. The find indirectly confirms the hypothesis that asteroids were one of the sources of water on the young Earth.
Other features
The average speed with which the objects of this region fly around the Sun is 20 km/s. At the same time, for one revolution, the asteroids of the main belt spend from three to nine Earth years. Most of them are characterized by a slight inclination of the orbit to the plane of the ecliptic - 5-10º. However, there are also objects whose flight path makes a more impressive angle with the plane of rotation of the Earth around the star, up to 70º. This characteristic formed the basis for the classification of asteroids into two subsystems: flat and spherical. The inclination of the orbits of objects of the first type is less than or equal to 8º, the second - more than the specified value.
Rise
In the century before last, the hypothesis of the dead Phaeton was widely discussed in scientific circles. The distance from Mars to Jupiter is quite impressive, and another planet could orbit here. However, such ideas are now considered obsolete. Modern astronomers adhere to the version that in the place where the asteroid belt passes, the planet simply could not have arisen. The reason for this is Jupiter.
The gas giant, even in the early stages of its formation, had a gravitational effect on the area that lay closer to the Sun. He attracted a part of the substance from this zone. The bodies not captured by Jupiter were scattered in different directions, the speeds of protoasteroids increased, and the number of collisions increased. As a result, they not only did not increase their mass and volume, but even became smaller. In the process of such transformations, the probability of a planet appearing between Jupiter and Mars became equal to zero.
Permanent influence
Jupiter and today "does not leave alone" the asteroid belt. Its powerful gravity causes changes in the orbits of some bodies. Under its influence, the so-called forbidden zones appeared, in which there are practically no asteroids. A body flying here due to a collision with another object is pushed out of the zone. Sometimes the orbit changes so much that it leaves the asteroid belt.
Additional rings
The main asteroid belt is not alone. On its outer border are two more less impressive similar formations. One of these rings is located directly in the orbit of Jupiter and is represented by two groups of objects:
- “Greeks” lead the gas giant by about 60º;
- Trojans are the same number of degrees behind.
A characteristic feature of these bodies is the stability of their movement. It is possible due to the location of asteroids at the "Lagrange points", where all gravitational effects on these objects are balanced.
Despite its relatively close location to Earth, the asteroid belt has not been studied enough and holds many secrets. The first of these, of course, is the origin of the small bodies of the solar system. The existing assumptions on this score, although they sound quite convincing, have not yet received unambiguous confirmation.
Raise questions and some features of the structure of asteroids. It is known, for example, that even related objects of the belt differ quite strongly from each other in some parameters. The study of the characteristics of asteroids and their origin is necessary both to understand the events preceding the formation of the solar system in the form known to us, and to build theories about the processes occurring in remote parts of space, in systems of other stars.
