The description of the solar system contains not only information about 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 composer Charles Burney. The word is of Greek origin and means "star-like." The use of this term was due to the fact that when studying the expanses of space through a telescope, asteroids seemed like stars: they looked like points, unlike planets that resembled disks.
As such, there is no definition of the term today. The main characteristic feature of objects of the asteroid belt and similar structures is size. The lower limit is 50 m in diameter. Smaller cosmic bodies are already meteors. The upper boundary 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. About 98% of the latter are objects of the asteroid belt, remote 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. The next largest Vesta, Pallas and Hygea, together with Ceres, make up 51% of the total mass of the asteroid belt.
The form
The cosmic bodies that make up the belt, in addition to dimensions, have a number of basic characteristics. All of them are stony objects orbiting 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. Images taken by spacecraft flying through the asteroid belt in the solar system confirmed these assumptions. According to scientists, this form is the result of frequent collisions of asteroids with each other and other objects.
Composition
To date, astronomers distinguish three classes of asteroids according to the main substance that is part of them:
- carbon (class C);
- silicate (class S) with a predominance of silicon;
- metal (class M).
The former account for approximately 75% of all known asteroids. Such a classification, however, is not considered acceptable by some scientists. 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 discovered on the surface of Themis, a fairly large object in this zone, water ice. The find indirectly confirms the hypothesis that asteroids were one of the sources of water on young Earth.
Other characteristics
The average speed with which objects of this region fly around the Sun is 20 km / s. At the same time, asteroids of the main belt spend from three to nine Earth years on one revolution. Most of them are characterized by a slight inclination of the orbit to the ecliptic plane - 5-10º. However, there are also objects whose flight path amounts to a more impressive angle, up to 70º, with the plane of the Earth's rotation around the star. 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.
Occurrence
In the century before last, in the scientific community, the hypothesis of the deceased Phaeton was widely discussed. The distance from Mars to Jupiter is quite impressive, and here the orbit of another planet could pass. However, such ideas are now considered obsolete. Modern astronomers adhere to the version that at the place where the asteroid belt passes , the planet simply could not arise. The reason for this is in Jupiter.
The gas giant, even in the early stages of its formation, exerted a gravitational effect on the region lying 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 protoasteroid speeds increased, the number of collisions increased. As a result, they not only did not increase mass and volume, but even became smaller. In the process of such transformations, the probability of a planet between Jupiter and Mars has become equal to zero.
Constant influence
Jupiter today "does not leave alone" an asteroid belt. Its powerful gravity causes a change 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 on the orbit of Jupiter and is represented by two groups of objects:
- "Greeks" are ahead of the gas giant by about 60º;
- Trojans are lagging the same number of degrees.
A characteristic feature of these bodies is the stability of their movement. It is possible due to the location of asteroids in the "Lagrange points", where all the gravitational effects on these objects are balanced.
Despite its relatively close proximity to the 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 in this regard, although they sound quite convincing, have not yet received unequivocal confirmation.
Some structural features of asteroids also raise questions. It is known, for example, that even related objects of the belt in some respects are quite different from each other. The study of the characteristics of asteroids and their origin is necessary both for understanding the events preceding the formation of the solar system in a form known to us, and for constructing theories about the processes taking place in remote parts of space in systems of other stars.