Deimos and Phobos are small by satellite standards satellites of our neighbor, Mars. Despite their formidable names, they look modest against the background of the rest of the celestial bodies of the solar system. Nevertheless, “Fear” and “Horror” accompanying Mars in its eternal orbit, are of great value to researchers and cause considerable interest among astrophysicists.
Writer prediction
Few know that the discovery of the satellites of Mars for the first time did not occur at the observatory, but on the pages of the famous work of Jonathon Swift's "The Adventures of Gulliver." In one of the chapters, scientists from the flying island of Laputa told the protagonist about two bodies discovered by them moving around Mars. The story of Gulliver's adventures appeared at the beginning of the eighteenth century. The scientific discovery of Phobos and Deimos took place much later - in 1877. It was made by A. Hall during the great confrontation of the Red Planet. The discovery is worthy of perpetuation for many reasons: it became possible thanks to the exceptionally good weather conditions and the incredible work of the scientist, in whose arsenal there were only quite imperfect tools of the late nineteenth century.
Crumbs
Deimos and Phobos are inaccessible to study with amateur equipment because of their modest size. They are many times smaller than the moon. The satellite Deimos is the smallest similar object in the entire solar system. Phobos is somewhat larger than its "brother", but also can not boast of impressive size. Since the beginning of the cosmonautics era, both objects have been studied using several devices: Viking-1, Mariner-9, Phobos, Mars Express. During the research, satellite images were obtained, as well as data on the nature of their surface and composition.
Origin
Today, the question of where the satellites from Mars came from is not completely clear. One likely version is that Deimos and Phobos are asteroids captured by the Red Planet. Moreover, it is assumed that they flew from remote areas of the solar system or even formed outside its borders. Less plausible, scientists call the hypothesis of the origin of satellites from the main asteroid belt. Perhaps a certain role in the appearance of such a retinue in Mars was played by the giant Jupiter, which, with its powerful gravitational field, distorts the orbits of all asteroids flying nearby.
"Fear"
Phobos is the satellite closest to the planet. Like Deimos, it has an irregular shape and moves in an almost circular orbit around Mars. Phobos is always turned to the planet on one side, which is similar to the moon. The reason for this is the coincidence of the periods of rotation of the body around Mars and around its axis.
The orbit of Phobos is located very close to the Red Planet. According to scientists, the satellite under the influence of the gravitational field of Mars is gradually decreasing (a little less than ten centimeters per year). In the distant future, he faces destruction. Either Phobos will fall on Mars after about 11 million years, or a little earlier, after 7 million years, it will be torn apart by the planet’s gravitational forces and form a ring of debris around it.
Surface
Phobos and Deimos are satellites covered in traces of meetings with meteorites. The surface of both is dotted with craters of different sizes. The largest of them is located on Phobos. The diameter of the crater is 10 km; for comparison, the size of the satellite itself is 27 by 21 km. The impact that left such a mark could easily lead to the complete destruction of this cosmic body.
The surface of Phobos has one more feature that distinguishes it from its “fellow”. These are almost parallel furrows up to several hundred meters wide, occupying a vast area. Their origin remains a mystery. According to scientists, they can also be the consequences of a powerful blow or be a consequence of the gravitational impact of Mars.
"Horror"
Deimos measures 15 by 12 kilometers and orbits in a more distant orbit than Phobos: the distance to the planet is about 23.5 thousand kilometers. The Horror makes one revolution around Mars in 30 hours and 18 minutes, which slightly exceeds the length of the day on the planet and is more than four times slower than the movement of Phobos. He has 7 hours and 39 minutes to fly around the planet.
Deimos, in contrast to his "brother" is not going to fall. Some scientists suggest that the likely fate of the “Horror” is to overcome the attraction of Mars and fly into space.
Structure
For a long time, it was not clear what Deimos and Phobos were hiding inside. Scientists knew only about the suspiciously low density of these bodies, calculated in the process of observations from the Earth. In connection with these data, the most fantastic assumptions arose about which objects accompany Mars. Phobos and Deimos, in some hypotheses, were listed as artificial hollow satellites created in ancient times and, possibly, by the civilization of another planet.
After studying the data obtained by spacecraft, it was found that the “retinue” of Mars is more like asteroids, that is, natural objects. The density of matter on the satellites was calculated - approximately 2 g / cm 3 . A similar indicator is found in some meteorites. Today, the low density of the satellites of Mars is explained by the peculiarities of their structure: presumably Phobos and Deimos consist of a mixture of rock, rich in carbon, with ice. In addition, images of spacecraft suggest that the surface of the object closest to Mars is covered with a meter-long layer of dust similar to the regolith of the Moon.
The “retinue” of the Red Planet still has many secrets, therefore, astronomers are constantly developing projects for flights to it. Of great interest is Mars itself. In some projects, he is seen as a candidate for terraforming or a suitable place for the extraction of certain resources. Also, in scientific circles, the fantastic prospect of placing research bases first on the Moon and then on Mars is rather seriously discussed at first glance. In addition, the study of such objects can always bring information not only about themselves, but also about the solar system, its formation and features. And even about the universe as a whole.