Over the past five years astronomers have counted in our Solar system, several dozen satellites (at the time of preparation of this article was 86), moving around their planets in the opposite direction to their rotation! They are called non-scheduled (as opposed to regular traded in the forward direction towards their planets).

It seems that irregular satellites appeared in the old days, when the gravitational effects of newborn planets tore smaller body with their original orbits and translated them on the back of the orbit. It became clear to scientists that the study of these processes can shed light on the early stage of the formation of the Solar system.

"Fellow-travelers" of giant planets.

Ironically, the first irregular satellite, called Triton, was discovered in 1846 the second to last of the known planets of the Solar system - Neptune. This satellite, we can say lucky because most irregular satellites because of their small size and low luminosity very difficult to detect. Moreover, unlike regular satellites, they are scattered in a large

the space. For example, the remote regular companion of Jupiter is at a distance of two million miles from the planet, as is known irregular satellites of Jupiter rotate away from him 30 million miles!

Recall that the planets-giants in our Solar system are Jupiter, Saturn, Uranus and Neptune. Until recently, for Jupiter "was listed as" 8 regular satellites and 55 irregular, with the Saturn - 21 regular and 26 irregular, with Uranium - 18 regular and 9 non-scheduled, with the Neptune - 6 regular and 7 irregular and Pluto - 1 regular partner. Now the picture has changed dramatically. It turned out that four giant planets have many irregular satellites. According to the extrapolation of the available astronomical data, each of giant planets, there should be approximately s t (!) irregular satellites with a diameter of more than a kilometer! In the system of satellites of Jupiter these sizes range from 180 kilometers (Gimalai) two kilometers from the smallest "fellow travelers." These satellites move in the most difficult in the Solar system - loop-like orbits. Because irregular accomplices are at a very great distance from their planets on them almost equally gravitational forces act of the planet and the Sun. The result is fast precession of the orbit of the satellite (rotation great its axis of the ellipse).

Rhythms of the cosmos.

If the specified corresponds to precession frequency of reference of the planet around the Sun, satellite resonates. In this situation gradually accumulate the effects of the sun's gravitation, deforming the satellite's orbit: the ellipse is drawn to such an extent that the satellite or encounters his planet, or breaks into gravitational "embrace" of the Sun! The analysis of the different impacts on the movement of the satellite has revealed in the system of Jupiter to 17 fragments crashed in the collision of a larger "companion".

One of the few well-studied irregular satellites is Saturn's moon Phoebe. He was investigated interplanetary space probe "Cassini" in June 2004. With its help was able to get a clear image of numerous craters and spectra of reflected sunlight evidencing on FEBE ice from water and carbon dioxide. Moons of Neptune, Triton and Nereid, investigated by ' Voyager-2". too, became covered with ice. Therefore, they formed away from the Sun.

The remains of the "building material".

There is reason to believe that irregular satellites are remnants of the "building material" from the formation of planets. Like asteroids and nuclei of comets, they first turned around the Sun, and then were captured planets. The famous comet chumacero-levy 9, for example, was captured complex gravitational interactions and appeared on a temporary orbit around Jupiter, after which in 1994 was torn apart by gravitational forces of the planet and fell on it. Had this not happened, after hundreds of years comet again would be a heliocentric orbit! Astronomers known several cases of return in the solar space objects after a temporary "capture" their Jupiter.

Options of capture.

in the 70-ies of the last century theorists have proposed three versions of the script capture of satellites. In the first variant of "candidate" in satellites if it is small in size, will burn up in the atmosphere of the planet, by which it is flying If a "candidate" is large in size, it will pass through it and continue your way along the orbit around the Sun. Only with average size of "lost" the celestial body will be captured by the planet.

The second capture mechanism is triggered in the growth stage of the planet. Asteroids and other "candidates" in satellites fall into a kind of gravitational trap because of sharply increased mass of the planet. As in the previous scenario, this option does not explain the presence of satellites of Neptune and Uranus, which has experienced a sharp increase of its mass.

In 1971, was offered a third option is of concern to us, which is based on the process of collision of two bodies in space. But it later emerged that the capture can occur without clashes. In may 2006, astronomers have offered a different variant of triple capture: it is the system of "Sputnik - Planeta" is broken by gravitational forces, one of the components is ejected from the system, and the second goes into its orbit.

Where did the "fellow travelers"?

According to the latest astronomical discoveries, all four giant planets in the Solar system is surrounded irregular satellites. In search of their origin, scientists have focused on the study of the script triple capture "candidates". It is a triple grip can explain almost the same number of irregular satellites of the giant planets.

But the question remains: where did these satellites? Scientists propose two possible answers to this question. According to the first variant, "candidates" could be the asteroids and the cores of comets, caught in the same area of the Solar system that has captured their planet. The second variant assumes that approximately 700 million years after the formation of the planets of the Solar system was heavily polluted by planetesimals ("germ" future of celestial bodies). At some point during the "taxi" major planets on their current orbits, and as a result of strong gravitational interactions of Saturn and Jupiter myriad of asteroids and comets were scattered in space. Some of these wandering bodies could be captured by large planets. The main part of the scattered "candidates" in satellites focused beyond the orbit of Neptune in the so-called Kuiper belt.

Prospects.

Now actively continues the study of the systems of irregular satellites. Already managed to prove that captures of "candidates" in these satellites was in the early stages of the evolution of the Solar system, because in the later times of the conditions for this were gone. Furthermore, the similarity of the systems of irregular satellites of the giant planets indicates the appearance of these "fellow travelers" in the triple capture is the only mechanism that is appropriate for both Neptune and Jupiter, So irregular satellites, sosredotochimsya around giant planets, keep memory about events that happened millions of years ago.

G. Gordeev