On the outskirts of our star system is the Kuiper belt. It passes beyond the orbit of Neptune, so it was extremely difficult to make out anything in this space earlier. However, since powerful telescopes appeared at the person’s disposal, several discoveries have been made. So, for example, it became known that the trans-Neptune object is the main unit of the Kuiper belt, the Oort cloud, and the scattered disk. It is worthwhile to examine in more detail bodies rotating on the "margins" of the solar system.
TNO
Trans-Neptune object - a cosmic body orbiting a luminary. The most famous of these objects is Pluto, which until 2006 was considered a planet. However, today Pluto is the second largest trans-Neptune object. The average distance to the star of these bodies is greater than that of the extreme planet in our star system - Neptune.
Currently, more than one and a half thousand such facilities have been opened. However, scientists are inclined to believe that in fact there are much more.
The largest trans-Neptune object is Eris. It was opened in 2005. The body farthest from our luminary, which has no name and appears in the lists under the number V774104. It is 103 astronomical units distant from the Sun.
All TNOs are divided into four groups.
Isolated TNO
In the solar system, there is a subclass of this type of body: a separate trans-Neptune object. It is named so for the reason that the perihelion points of such bodies are located at a considerable distance from Neptune, which means that they do not experience the influence of its gravity. This situation makes these planets practically independent not only of Neptune, but also of the entire solar system as a whole.
Formally, these objects are the bodies of an extended scattered disk. Currently, there are data on nine such bodies, but this list is likely to be significantly increased in the near future.
One of the representatives of this TNO group is Varuna. Opened in November 2000.
Classic Kuiper Belt Objects
The name of this group of bodies comes from the numbering of the first of them - QB1. That is why the trans-Neptune object, which is located in the Kuiper belt, is called kyubivano (kyu-bi-uan). The orbit of these bodies lies outside the orbit of Neptune, while they themselves do not have a pronounced orbital resonance with the planet.
The orbits of most of the cuibivans have an almost circular shape, close to the plane of the ecliptic. A large part of these bodies is tilted at a very small angle, the other has significant tilt angles and more elongated orbits.
The main features of the bodies included in this group are the following:
- Their orbit never crossed with the orbit of Neptune.
- Objects are not resonant.
- Their eccentricity is less than 0.2.
- Their Tisserand criterion exceeds 3.
The classic representative of this group is Quavar, one of the largest bodies in the Kuiper belt. Opened in 2002.
Resonant TNO
Resonant are those trans-Neptune objects whose orbit is in orbital resonance with Neptune.
A close study of such objects makes it possible to talk about the narrowness of the boundaries of resonant objects. In order to remain invariably within these limits, the body needs energy in a certain amount, no more, but no less. It is very simple to get the orbit out of resonance: an insignificant deviation of the semimajor axis from the established boundaries is enough.
As the discovery of new objects revealed that more than a tenth of them is in resonance 2: 3 with Neptune. It is believed that this ratio is not accidental. Most likely, these objects were collected by Neptune during migration in more distant orbits.
Before the first trans-Neptune object was discovered, experts thought that the action of giant planets on a massive disk would lead to a decrease in the semi-axis of Jupiter and an increase in the semi-axes of Uranus, Neptune and Saturn.
One of the representatives of this group is Orc, a trans-Neptune object located in the Kuiper belt.
Scattered disc objects
These are bodies located in the most remote region of our star system. The density of objects in this area is very low. All bodies of a scattered disk are made of ice.
The origin of this area is not really clear. Most scientists are inclined to believe that it was formed at a time when the gravitational impact of the planets had an insufficient effect on the Kuiper belt, as a result of which its objects were scattered over a much larger area than in our time. A scattered disk, compared to the Kuiper belt, is a variable medium. The bodies in it travel not only in the "horizontal" direction, but also in the "vertical", moreover, at almost the same distances. Computer simulation showed that some of the objects can have wandering orbits, and some are unstable. This suggests that bodies could be thrown into the Oort cloud or much further.
New discovery
In July 2016, another trans-Neptune object was discovered. Its dimensions are very small (diameter - about 200 km), it is 160 thousand times dimmer than Neptune. Its name is translated from Chinese as "rebel." The object received such a name because it rotates in the direction opposite to the movement of the solar system, since this can only be explained by the fact that some sufficiently powerful body acted on it, radically changing its orbit.
This nature of the new object made scientists bewildered, because at the moment it is not clear which planet and how could make the "rebel" move in such an orbit. Astronomers again think about the existence of an unknown planet that can have such powerful effects on other bodies.