Deimos and Phobos are small by cosmic standards satellites of our neighbor, Mars. Despite their rather formidable names, they look modest against the background of other celestial bodies in the solar system. Nevertheless, "Fear" and "Horror", which accompanies Mars in its eternal orbit, are of great value to researchers and arouse considerable interest among astrophysicists.
Writer's Prediction
Few people know that the discovery of the satellites of Mars for the first time took place not in the observatory, but on the pages of the famous work of Jonathon Swift "The Adventures of Gulliver". In one of the chapters, scientists from the flying island of Laputa told the main character about the two bodies they discovered 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 was made possible thanks to exceptionally favorable weather conditions and the incredible work of a scientist who had only rather imperfect tools of the late nineteenth century in his arsenal.
Babies
Deimos and Phobos are not available for study with amateur equipment due to their modest size. They are many times smaller than the moon. Deimos is the smallest such object in the entire solar system. Phobos is somewhat larger than its "brother", but also cannot boast of impressive size. Since the beginning of the era of cosmonautics, both objects have been studied using several devices: Viking-1, Mariner-9, Phobos, Mars Express. In the process of research, images of satellites were obtained, as well as data on the nature of their surface and composition.
Origin
Today, the question of where Mars got satellites from is not completely clear. One of the likely versions says that Deimos and Phobos are asteroids captured by the Red Planet. Moreover, it is assumed that they arrived from remote parts of the solar system or even formed outside its borders. Scientists call the hypothesis of the origin of satellites from the main asteroid belt less plausible. Perhaps, the giant Jupiter played a certain role in the appearance of such a “retinue” on Mars, with its powerful gravitational field distorting the orbits of all asteroids flying nearby.
Fear
Phobos is the closest satellite 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.
Phobos orbit is very close to the Red Planet. According to scientists, the satellite under the influence of the gravitational field of Mars is gradually decreasing (slightly less than ten centimeters per year). In the distant future, it is threatened with destruction. Either Phobos will fall on Mars in about 11 million years, or a little earlier, in 7 million years, it will be torn apart by the gravitational forces of the planet and forms a ring of debris around it.
Surface
Phobos and Deimos are satellites covered with traces of meteorite encounters. The surface of both is dotted with craters of various 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. An impact that left such a mark could easily lead to the complete destruction of this cosmic body.
The surface of Phobos has another feature that distinguishes it from its "brother". These are practically parallel furrows up to several hundred meters wide, occupying a vast area. Their origin remains a mystery. According to scientists, they may also be the consequences of a powerful impact or be a consequence of the gravitational influence of Mars.
Horror
Deimos has dimensions of 15 by 12 kilometers and circles in an orbit more distant than Phobos: the distance to the planet is approximately 23.5 thousand kilometers. Horror makes one revolution around Mars in 30 hours and 18 minutes, which is slightly longer than the duration of the day on the planet and more than four times slower than the movement of Phobos. Himenough to fly around the planet 7 hours and 39 minutes.
Deimos, in contrast to his "brother" is not going to fall. Some scientists suggest that the Horror's likely fate is to overcome the gravity of Mars and fly into space.
Building
For a long time it remained unclear 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 what objects accompany Mars. Phobos and Deimos, in some hypotheses, were listed as artificial hollow satellites created in ancient times and, possibly, by a 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 satellites was calculated - approximately 2 g/cm3. 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 carbon-rich rock with ice. In addition, spacecraft images 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 keeps a lot of secrets, so astronomers are constantly developing projects for flights to it. Mars itself is of great interest. In some projects it is considered asa candidate for terraforming or a suitable place to mine some resources. Also in scientific circles, the seemingly fantastic prospect of placing research bases first on the Moon and then on Mars is being seriously discussed. 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.
